Rectification

Rectification O N - L I N E

M A N U A L

Copyright  1982 - 1999 by ERDAS, Inc. All rights reserved. Printed in the United States of America. ERDAS Proprietary - Delivered under license agreement. Copying and disclosure prohibited without express written permission from ERDAS, Inc. ERDAS, Inc. 2801 Buford Highway, N.E. Atlanta, Georgia 30329-2137 USA Phone: 404/248-9000 Fax: 404/248-9400 User Support: 404/248-9777

Warning All information in this document, as well as the software to which it pertains, is proprietary material of ERDAS, Inc., and is subject to an ERDAS license and non-disclosure agreement. Neither the software nor the documentation may be reproduced in any manner without the prior written permission of ERDAS, Inc. Specifications are subject to change without notice.

Trademarks ERDAS is a trade name of ERDAS, Inc. ERDAS and ERDAS IMAGINE are registered trademarks of ERDAS, Inc. Model Maker, CellArray, ERDAS Field Guide, and ERDAS Tour Guides are trademarks of ERDAS, Inc. Other brands and product names are trademarks of their respective owners.

Rectification On-Line Manual Raster Image Rectification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Geometric Correction Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Fast Linear Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Rectification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Display the Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Ground Control Points (GCPs) . . . . . . . . . . . . . . . Corresponding GCPs . . . . . . . . . . . . . GCPs in IMAGINE Files . . . . . . . . . . . . The input image file can be set to: . . . . . . . . What happens when a reference source is selected: . Input and Reference . . . . . . . . . . . . . .

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Recording and Editing GCPs . . . . . . . . . . . . Viewer. . . . . . . . . . . . . . . . . Tablet . . . . . . . . . . . . . . . . . Using the GCP Tool with a Digitizing Tablet . Keyboard . . . . . . . . . . . . . . .

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Selecting GCPs . . . . . . . . . . . . Operations on Selected GCPs . Moving a GCP . . . . . . . Deleting a GCP . . . . . . .

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Editing GCPs in Linked Viewers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Transformation Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Calculating the Transformation Matrix from GCPs Selected GCPs . . . . . . . . . . . . . Automatic Calculation . . . . . . . . . . Minimum Number of GCPs . . . . . . . .

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Calculate Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Direction of Transformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Reprojection Grid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Resampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

RMS Error Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Residuals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 RMS Error Per GCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Total RMS Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Error Contribution by Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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Rectification On-Line Manual Linear Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Viewer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Scale in the Viewer vs. a File . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Offset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Offset in Rectification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Set Geo Correction Input File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Set Geometric Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Affine Model Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Camera Model Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Change DEM Source for Camera model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Landsat Model Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Change DEM Source for Landsat model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Polynomial Model Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Load CFF File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 WINDOWS Only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Reprojection Model Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Rubber Sheet Model Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Spot Model Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

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Rectification On-Line Manual Change DEM Source for Spot model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Geometric Correction Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Calibrate Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 GCP Tool Reference Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Reference Map Projection Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 GCP Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 GCP Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Nominal Cell Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 GCP Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Recalculate Output Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Reference Map Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Resample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 GCP Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

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Raster Image Rectification

Raster Image Rectification Geometric Correction Tools ERDAS IMAGINE provides tools for simple linear corrections as well as tools for image-to-image registration or image-to-map rectification using ground control points.

➲ Many of the terms used here to explain the rectification process are defined in the “Rectification” chapter in the ERDAS Field Guide.

Fast Linear Adjustments Under the View menu of the Viewer menu bar, you can use any of the following options to make fast, simple, linear (1st-order) corrections:

♦ The Rotate dialog lets you specify the number of degrees and the direction in which to rotate the Viewer image.

♦ Screen Flip Vertically and Screen Flip Horizontally options will instantly flip (reflect) the Viewer image.

♦ The Viewer - Linear Adjustment dialog provides options to rotate, scale (resizing), offset (moving the image within the Viewer window), and reflect an image.

Rectification When rectifying an image, you will use ERDAS IMAGINE to:

♦ record ground control points (GCPs), ♦ compute a transformation matrix, and ♦ use that transformation matrix and a resampling method to rectify the image. ☞ If you are reprojecting georeferenced data from one map projection to another, there is a shortcut for generating GCPs and calculating a transformation matrix using a reprojection grid. Display the Data To begin, display the data to be rectified in a Viewer window. If necessary, use the Arrange Layers dialog under the View menu to ensure the layer to be rectified is the top layer.

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Raster Image Rectification Then, select Raster | Geometric Correction... from the Viewer menu bar. This will open the Set Geometric Model dialog. After selecting a model type, click the Set Projection from GCP Tool... button on the Projection tab. When you select a type of reference from the GCP Tool Reference Setup dialog, and click Ok, the GCP Tool dialog opens. The GCP Tool allows you to record and edit GCPs. To calculate a transformation matrix from GCPs, you must have both input and reference coordinates in the cell array.

Ground Control Points (GCPs) A ground control point is a location within an image for which the map coordinates are known. To be useful in rectification, the coordinates of a GCP must be known in the system to which the data are being rectified (e.g. lat/lon). Corresponding GCPs Any ERDAS IMAGINE image can have one GCP set associated with it. The GCP set is stored in the image file (.img) along with the raster layers. If a GCP set exists for the top raster layer that is displayed in the Viewer, then those GCPs can be displayed when you bring up the GCP Tool.

☞ Multiple sets of GCP data associated with an individual image should be stored as .gcc files. In the cell array of GCP data that is opened in the GCP Tool, one column shows the point ID of each GCP. The point ID is a name given to GCPs in separate files that represent the same geographic location. Such GCPs are called corresponding GCPs. A default ID string is provided (e.g. “GCP #1”), but you can enter your own unique ID strings to set up corresponding GCPs as needed. Even though only one set of GCPs is associated with an image file, one GCP set can include GCPs for a number of rectifications by changing the point IDs for different groups of corresponding GCPs. GCPs in IMAGINE Files GCPs that are digitized in a Viewer are stored with the raster data that are opened in the Viewer. However, GCPs can also be recorded from a digitizing tablet or straight from the keyboard. In these cases, they are stored alone in IMAGINE files with the extension .gcc. The input image file can be set to:

♦ Existing Viewer ♦ Image Layer (New Viewer) ♦ Vector Layer (New Viewer) ♦ Annotation Layer (New Viewer) 2

Raster Image Rectification

♦ GCP File (.gcc) ♦ ASCII File ♦ Digitizing Tablet (Current Configuration) ♦ Digitizing Tablet (New Configuration) ♦ Keyboard Only What happens when a reference source is selected: If GCP data exists for the reference, then those GCPs will be sorted in the GCP Tool to correspond to the input GCPs, according to their point IDs. If applicable, you can interactively edit GCPs and calculate and edit the transformation matrix with the GCP Tool until the RMS error is acceptably low. The residuals, RMS error, and contribution fields in the GCP Tool are not editable. These automatically update as you edit the GCPs and recalculate the transformation. Input and Reference When two Viewers are used, they are distinguished from one another as the input Viewer and the reference Viewer. When you are working with two sets of GCPs:

♦ input GCPs, which are in file coordinates and are digitized in the Viewer from which you started the GCP Tool (the input Viewer), and

♦ reference GCPs, which are the known map coordinates of the corresponding source GCPs. The input Viewer always opens the data to be rectified to the reference coordinate system.

Recording and Editing GCPs Viewer To digitize GCPs in a Viewer, you can use:

♦ the Viewer window (input or reference), ♦ any Viewer that is linked to that Viewer, ♦ the chip extraction Viewer, which magnifies the source Viewer 4 times, and ♦ the CellArray of GCPs in the GCP Tool. 3

Raster Image Rectification To add a GCP graphically, select the cross hair icon from the GCP Tool tool bar.

Then, left-click in a Viewer to digitize a new GCP at that location. Tablet When you select Digitizing Tablet (New or Current Configuration) from the GCP Tool Reference Setup dialog, other dialogs are opened that allow you to set up your digitizer for this session. Then, any points you digitize on the tablet are recorded as reference GCPs. Using the GCP Tool with a Digitizing Tablet For each set of coordinates in the GCP Tool CellArray, there is a column with an arrow (>) pointing to the current GCP. You can left-click on any cell in the > column to change the current GCP. Whenever you digitize a GCP in a Viewer or with the tablet, you will overwrite the current GCP. The last entry in the CellArray is always blank, so that you can use it to digitize a new GCP. Keyboard To enter or edit a GCP from the keyboard, use the CellArray of GCP coordinates. The X Source, Y Source, X Dest, and Y Dest cells are editable. When you edit a GCP in the CellArray, the GCP will move in the Viewer if it is opened.

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The GCP Tool has been updated to use a pseudo map coordinate system rather than a file coordinate system of the image when the image is un-georeferenced. The file coordinates for a pixel value in an image are in the Column and Row indices used to locate that value in the raster array of the image. An un-georeferenced image is normally displayed so that the upper left corner of the image represents file coordinate (0,0). The positive Column (X) direction is to the right, and the positive Row (Y) direction is downwards. When using the GCP Tool in early versions of ERDAS IMAGINE (such as V8.2), the coordinates for an un-georeferenced image were reported using the file coordinate system. In ERDAS IMAGINE V8.3 and above, the file coordinate system definition is unchanged (the Inquire Cursor in File coordinate mode reports coordinates with the positive Y direction being downwards from a 0,0 origin at the top left corner of the image), but the GCP Tool now references an image using the pseudo map coordinate system if it is un-georeferenced (or its real map coordinate system if it is georeferenced). In this system, the origin (0,0) is still at the top left of the image, but the positive Y direction is upwards.

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Raster Image Rectification

This change has been made to standardize the coordinate systems used by ERDAS IMAGINE and to provide added functionality (such as being able to specify relative placements for un-georeferenced images by changing the pseudo origin). Consequently, Y coordinates for un-georeferenced images are now negative, since the image rows are, by definition, below the origin of the coordinate system. The use of the pseudo map system by the GCP Tool may cause some problems if you have sets of coordinates referenced in the old manner. For instance, if you have Ground Control Points measured in ERDAS IMAGINE V8.2 as file coordinates, they will no longer be appropriate for use in the ERDAS IMAGINE V8.3 (and above) GCP Tool. This can easily be solved using the Formula capability of the CellArray. Import the coordinates into a CellArray (for instance, the GCP Tool or Coordinate Calculator) and highlight the column representing the Y file coordinates. Right-click the Column header to get the Column Options menu. Select Formula. Specify the formula as: * (-1). The coordinates should now be pseudo map coordinates that may be used in ERDAS IMAGINE V8.3 and above. Similarly, if you have another software package that expects the Y file coordinates to increase positively downwards, use the CellArray Formula option to convert ERDAS IMAGINE V8.3 (and above) pseudo map coordinates to the correct format before exporting them. To do this, use the same formula as above (i.e., * (-1).

Selecting GCPs Selection is useful when moving GCPs graphically, deleting GCPs, or computing a transformation matrix with a subset of the GCPs in the cell array. You can select GCPs graphically (in the Viewer) or in the GCP CellArray. These selections operate independently unless you specify Input options or Reference options to transfer selections.

♦ To select a GCP graphically in the Viewer, use this icon:

and select it as you would an annotation element.

♦ To select GCPs in the cell array, use the cell array selection options.

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Raster Image Rectification Operations on Selected GCPs When GCPs are selected in the CellArray, you can set their point type under the edit menu in the GCP Tool. Transformation matrix is calculated on control points, while check points are used for accuracy verification. The point type also limits GCP prediction and GCP matching to work with only control points. Moving a GCP You can move a GCP to another location in the Viewer by selecting it and dragging it to its new location. You can also left-click on any GCP coordinate in the CellArray to enter new coordinates. Deleting a GCP To delete a GCP, use the CellArray in the GCP Tool.

Editing GCPs in Linked Viewers The graphic editing of GCPs can be done in linked Viewer windows, so that you can edit your GCPs in imagery of different resolutions, or in Viewers using different band combinations. Use chip extraction in Input or Reference to conveniently open a linked Viewer at 4X magnification using cubic convolution resampling (for continuous data). Any number of other linked views is possible.

☞ The precision of the GCP coordinates depends upon the resolution of the Viewer in which the GCP is digitized or moved.

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Transformation Matrix

Transformation Matrix A transformation matrix is a set of numbers computed from the GCPs that can be plugged into polynomial equations. These numbers are called the transformation coefficients. The polynomial equations are used to transform the coordinates from one system to another. The Transformation tab on the selected Model Properties dialog shows you a scrolling list of the transformation coefficients in the transformation matrix. They are calculated with the GCP Tool’s Solve Geometric Model with Control Points button.

Calculating the Transformation Matrix from GCPs To calculate a transformation matrix from GCPs, use the GCP Tool, and click the Solve Geometric Model with Control Points button. Selected GCPs You can base your calculations on all the GCPs in the cell array, or on selections in the cell array. Selected GCPs are calculated only on the control points. Your selection may change as you view the RMS error and contribution of each point, as shown in the right side of the GCP CellArray (scroll right to view these columns). Automatic Calculation You can also click the Set Automatic Transformation Calculation button, to compute the transformation in real-time as you edit the GCPs or change the selection in the CellArray. With the Set Automatic Transformation Calculation button, you can move a GCP in the Viewer while watching the transformation coefficients change on the Transformation tab in the selected Model Properties dialog, and the errors change in the GCP Tool. Minimum Number of GCPs A minimum number of points is necessary to calculate the transformation, depending on the order of the transformation. This number of points is:

(t + 1)(t + 2) -------------------------------2 where t is the order of the transformation. If the minimum number of points is not satisfied, then an error message dialog is opened. The coefficients in the Transformation tab, RMS errors, and residuals in the GCP Tool will be blank. At this point, you won’t be allowed to save the transformation or resample the data.

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Transformation Matrix

☞ Use more than the minimum number of GCPs whenever possible. Although it is possible to get a perfect fit, it is rare no matter how many GCPs are used. To change the order of the transformation, use the Parameters tab in the selected Model Properties dialog.

Calculate Error The transformation matrix contains the coefficients for transforming the reference coordinate system to the input coordinate system. Therefore, the units of the residuals and RMS errors are the units of the input coordinate system.

Direction of Transformation By default, the transformation matrix in the reference-to-input transformation converts reference coordinates to the input coordinate system. Although this may sound backwards, this is the transformation that is actually used in the resampling process.

Reprojection Grid The Reprojection Model Properties dialog provides a “shortcut” for reprojecting data from one map projection system to another. By this method, input GCPs are generated automatically from a grid on the source data that you specify, and the corresponding reference GCPs are computed from map projection data that you provide. These GCPs are derived and used transparently. They do not appear in the GCP Tool, nor are they stored to a file. In the Reprojection Model Properties dialog, you enter Grid Sampling X and Grid Sampling Y, which is the number of GCPs in the X and Y dimensions of a grid. For example, if you specify a grid sampling density of 8 in the X direction and 8 in the Y direction, there will be 64 GCPs (8 × 8 = 64) sampled in a grid pattern across the source data. (You will not see this grid in the Viewer.) From those GCPs, a transformation matrix is calculated. RMS error information is displayed in the Reprojection Model Properties dialog. You can use the transformation coefficients to create an output image using the Resample dialog.

Resampling Resampling is the process of calculating the file values for the rectified image, and creating the new file. Resampling requires an input file and a transformation matrix, by which to create the new pixel grid. When you are ready to perform the transformation using the current transformation matrix, use the Resample dialog.

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Transformation Matrix All of the layers of the top layer(set) in the input Viewer window will be resampled. The output image will have as many layers as the input image. ERDAS IMAGINE provides these widely-known resampling algorithms:

♦ Nearest Neighbor - uses the value of the closest pixel to assign to the output pixel value. ♦ Bilinear Interpolation - uses the data file values of four pixels in a 2 x 2 window to calculate an output value with a bilinear function.

♦ Cubic Convolution - uses the data file values of 16 pixels in a 4 x 4 window to calculate an output value with a cubic function.

➲ For more information on these resampling methods, see the Rectification chapter in the ERDAS Field Guide.

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RMS Error Calculation

RMS Error Calculation This document discusses how RMS error and related values are calculated when a transformation matrix is calculated from GCPs. A transformation matrix is tested by comparing the known source GCP coordinates to coordinates for the same point in the input coordinate system that are calculated with the transformation matrix. The corresponding reference GCPs are retransformed to the input coordinate system using the reference-to-input transformation matrix. The distance between the input GCP coordinates and these retransformed coordinates is the RMS error. RMS error is calculated by the root means squared method using the following equation: RMS error =

2

( xr – xi ) + ( yr – yi )

2

where:

x i and y i are the source coordinates x r and y r are the retransformed coordinates RMS error is expressed as a distance in the input coordinate system. If data file coordinates are the input coordinates, then the RMS error is a distance in pixel widths. For example, an RMS error of 2 means that the reference pixel is 2 pixels away from the retransformed GCP.

Residuals The residuals are the distances between the input and retransformed coordinates in one direction. They are shown for each GCP in the “X Residual” and “Y Residual” columns of the GCP Tool.

♦ X Residual is the distance between the source X coordinate and the retransformed X coordinate.

♦ Y Residual is the distance between the source Y coordinate and the retransformed Y coordinate.

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RMS Error Calculation

RMS Error Per GCP The “RMS Error” column in the GCP Tool shows the RMS error of each GCP. This is calculated with a distance formula:

Ri =

2

2

X Ri + Y Ri

where:

R i = the RMS error for GCP i X R i = the X Residual for GCP i Y R i = the Y Residual for GCP i The illustration below demonstrates the relationship between residuals and RMS error per point. source GCP

X Residual RMS Error

Y Residual retransformed GCP

11

RMS Error Calculation

Total RMS Error From the residuals, the following calculations are made to determine the total RMS error, and the X RMS error and Y RMS error. These totals appear in the GCP Tool.

R x , R y , and T are calculated as follows:

Rx =

1 --n

n

∑ X Ri

2

i=1

Ry =

1 --n

n

∑ Y Ri

2

i=1

T =

2 2 Rx + Ry =

1 --n

n

∑ X Ri + Y Ri 2

2

i=1 where:

R x = X RMS error R y = Y RMS error T = total RMS error n = the number of GCPs i = GCP number X R i = the X Residual for GCP i Y R i = the Y Residual for GCP i

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RMS Error Calculation

Error Contribution by Point The values in the “Contribution” column of the GCP Tool table are normalized values representing each point’s RMS error in relation to the total RMS error.

Ri E i = ----T where:

E i = error contribution of GCP i R i = the RMS error for GCP i T = total RMS error

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Linear Adjustments

Linear Adjustments A linear adjustment is a 1st-order (linear) correction of a grid. In the case of raster data, it is the conversion of the pixel grid from one plane to another using a linear transformation.

➲ For more information about 1st-order rectification, see the “Rectification” chapter of the ERDAS Field Guide. Viewer The Viewer - Linear Adjustment dialog controls the linear adjustment for the Viewer. Adjustments made here immediately affect the data in the Viewer. The parameters of these linear adjustments can be entered into the Affine Model Properties dialog to be used for rectification.

Scale Scale is a ratio of distance as represented on an image or map to the same distance as represented on another image or map, or to that distance on the ground. Scale is an expression of relative size. In terms of raster data, a change of scale in the X direction will affect the image horizontally, changing its width. Likewise, a change of scale in the Y direction will change the height of the image. Scale in the Viewer vs. a File

♦ Scale is the same as zoom in the Viewer, except that by using the Viewer - Linear Adjustment dialog, you can use scale options to set the X and Y scales independently.

♦ In the Affine Model Properties dialog, for rectifying an image file, a change in the scale will change the area that is represented by each pixel in the output image. A negative scale value can be used to specify a reflection of an image, although this is not the most convenient method. See the section on Reflection below for more information.

Offset Offset moves the image by a number of pixels in the input image. For example, if you specify an offset in the Viewer when an image is reduced, the image will be offset by that number of reduced pixels.

♦ A positive X offset moves the image to the right. A negative X offset moves the image to the left.

♦ A positive Y offset moves the image down. A negative Y offset moves the image up.

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Linear Adjustments Offset in Rectification In the Resample dialog, the defaults for the Output Corners are set so that the output data will start in the upper left corner of the new output file. This will remove any offset that is built in to the transformation matrix. To keep the offset that is specified in the transformation matrix, reset these fields to zero (0).

Rotation Rotation is specified in degrees (360 degrees is a full rotation), either clockwise or counterclockwise. When you rotate an image in the Viewer, it rotates around its center pixel.

Reflection Reflection lets you “flip” an image left to right, top to bottom, or both. In the Linear Adjustment dialog, there are icons with the letter R that demonstrate the reflection options. Reflection can also be accomplished by setting a negative scale. (However, specifying a reflection in the Linear Adjustment dialogs does not make the scale value negative as it appears in the dialog.) An image is always reflected around an axis that goes through the center of the image, and is absolutely horizontal or vertical. For example, if you reflect left-to-right an image that is already rotated 45 degrees in the Viewer, it will be reflected around an axis that is vertical in the Viewer, not an axis that is rotated 45 degrees.

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Calibration

Calibration Typically, when an image is georeferenced, a transformation matrix is used to resample the source image in order to create an output image whose pixels are aligned with a given map system. In ERDAS IMAGINE there is a mechanism called Calibration which allows the transformation matrix to be stored in the original image, so that the Viewer may compute proper map coordinates for the image without having to run through the process of resampling. This results in a saving of time and disk space since no additional file is created. The calibration is stored in the .img file in a record called Calibration. It can be viewed with HfaView in the Viewer. The Calibration record contains map information, projection information, and two polynomials (transformation matrices). One of the polynomials is used to convert from file coordinates to map coordinates. The other is used to convert from map coordinates to file coordinates. (Both are saved because polynomials of order greater than one cannot always be inverted correctly.) The calibration record is created by one of two means. The first is by the AVHRR and the SPOT importers. Each of these has a check box which allows you to indicate that the calibration is to be created using the information available in the header of the tapes or CD-ROMs. The AVHRR importer creates a second-order transform which converts file pixel coordinates to Latitude/ Longitude (in degrees). The SPOT importer creates a similar first-order transform for 1A and 1B, which converts file pixels to Latitude/Longitude. First-order is used because the SPOT header provides only five known points (the four corners and the center) and a minimum of six points is needed for a second-order transform. SPOT level 2 is already georeferenced and resampled, so there is no calibration created when importing these images. The second means of creating the calibration record is through the use of the GCP Tool. You use these tools to collect ground control points which are used to compute the transformation matrix. The Geometric Correction Tools dialog allows you to compute and save the calibration. Once this is done the image must be reopened for the calibration record to take effect. To recalibrate an image use the Edit | Delete Map Model option from the Image Info menu bar. Once the calibration is deleted, the image may be redisplayed in the Viewer and then recalibrated. Once an image is calibrated, the Inquire Cursor and the Measurement Tool may be used to read map coordinates and measure distances and areas. Additionally, any annotation created on a calibrated layer may be displayed on top of other georeferenced images. When the Viewer opens a calibrated image, you may use the Inquire Box, Measurement Tool, etc., to read the map coordinates for which it was calibrated. Annotation and Vector layers may also be opened on a calibrated image.

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Set Geo Correction Input File

Set Geo Correction Input File This dialog opens when you click the DataPrep icon in the ERDAS IMAGINE icon panel and then select Geometric Correction... from the Data Preparation menu.

Select Image to Geometrically Correct: Select to rectify an image from a Viewer or enter the name of an image file in the filename part. From Viewer

Click this radio button to select to rectify an image in a Viewer.

Select Viewer...

Click to select the Viewer containing the image you want to rectify.

From Image File Click this radio button to select to rectify an image file that is not currently displayed in a Viewer. Input Image File: Enter the name of the image file you want to rectify.

OK Click to use your selections and close this dialog. Cancel Click to cancel your selections and close this dialog. Help Click to view this On-Line Help document.

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Set Geometric Model

Set Geometric Model This dialog enables you to create a new geometric model from a template, select an existing geometric model, or use an image that is calibrated. This dialog opens when you select Raster | Geometric Correction... from the Viewer menu or by selecting DataPrep | Image Rectification... from the ERDAS IMAGINE icon panel. It is also opened when you click the icon on the Raster tool palette.

Select Geometric Model: Select a geometric model template from the list of available model types. A dialog for that model type is then opened for you to provide the specific parameters for creating a new geometric model. The new geometric model may be saved for later use. Affine Select this model and click OK to open the Affine Model Properties dialog. The affine geometric model allows the image to be flipped, rotated, or scaled. Camera Select this model and click OK to open the Camera Model Properties dialog. The camera model allows ortho-rectification of any camera data with a single perspective center. It is derived based on colinearity equations. The elevation data is used in the rectification process to remove relief displacement. ERS Select this model and click OK to open the Radar Model Properties dialog. This option is available only when the Advanced Radar module is installed. Landsat Select this model and click OK to open the Landsat Model Properties dialog. The Landsat model allows ortho-rectification of Landsat data, such as TM and MSS, which have multiple perspective centers. Polynomial Select this model and click OK to open the Polynomial Model Properties dialog. The polynomial geometric model uses polynomial coefficients to map between image spaces. The order of the polynomial may be from one up to five with no enforced upper limit. RADARSAT Select this model and click OK to open the Radar Model Properties dialog. This option is available only when the Advanced Radar module is installed. Reproject Select this model and click OK to open the Reprojection Model Properties dialog. This option is available only when the image has projection information. An input image already projected to a map space can be reprojected to another map system. The projection model is actually a polynomial approximation using a grid of regularly spaced points.

➲ For reprojection without using polynomial approximation or with multiple input files, see Reproject Images.

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Set Geometric Model Rubber Sheeting Select this model and click OK to open the Rubber Sheet Model Properties dialog. The rubber sheeting model uses piecewise polynomials for image rectification. This model should be used only when:

♦ the geometric distortion is severe ♦ GCPs are abundant ♦ no other geometric model is applicable Spot Select this model and click OK to open the Spot Model Properties dialog. The SPOT model allows ortho-rectification of SPOT panchromatic or multispectral (XS) data, which use pushbroom as their sensor. Even though SPOT 1B (systematically corrected) format is supported, it is more efficient to use SPOT 1A (raw) format for this model.

Open Existing Model... Click to open an existing geometric model saved from a previous session. The File Selector dialog is opened.

Use Existing Calibration This option is enabled only when the selected image is calibrated. Select this option to resample the image using the calibration data associated with it. The Geometric Correction Tools dialog is opened. Click the

tool to open the

Resample dialog.

OK Click to set the Geometric Model and close this dialog. Cancel Click to cancel the Geometric Model and close this dialog. Help Click to view the On-Line help for this dialog.

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Affine Model Properties

Affine Model Properties This dialog allows you to create a custom geometric correction model for affine calculations. This dialog opens when you click OK after selecting the Affine geometric model in the Set Geometric Model dialog.

Linear Adjustment Options: Scale

Allows you to scale the pixel size of the image.

X 1: Enter the scale factor for X. Y 1: Enter the scale factor for Y. Both 1: Enter the scale factor to apply the same scale to both X and Y. Offset

Allows you to set the offset from the origin of the image.

X: Enter the offset for X. Y: Enter the offset for Y. Rotate Angle: Enter the rotation angle in degrees. Initialize Click to reset the fields for Linear Adjustment Options and the Positive Rotation Direction to their defaults.

Positive Rotation Direction: Allows you to select which positive rotation to use for the image. Counter-Clockwise Click this radio button to select counter-clockwise positive rotation. Clockwise Click this radio button to select clockwise positive rotation.

Reflect Options: There are four reflection options:

Click this button to use no reflection.

Click this button to use an opposite reflection.

Click this button to use an upside-down reflection. 20

Affine Model Properties

Click this button to use an upside-down, opposite reflection.

Apply Click to accept these properties and proceed. Reset Click to reset to previously applied or solved properties. Save Click to save an affine model to disk. Save As Click to save to disk the affine model as a new file. Close Click to cancel these properties and close this dialog. Help Click to view this On-Line Help document.

21

Camera Model Properties

Camera Model Properties This dialog allows you to create a custom geometric correction model for a specific camera. This dialog opens when you click OK after selecting the Camera geometric model in the Set Geometric Model dialog. The camera model is for ortho-rectification of any image which uses camera as its sensor. The model is derived by space resection based on colinearity equations. The elevation information is required in the model for removing relief displacement. For orthorectifying multiple camera images in a single block, please see IMAGINE OrthoBASE.

General This tab allows you to customize basic information about this geometric correction model. Elevation Source:

Select the source of the elevation information for this image.

Use: Select whether to use DEM data or a constant value as the elevation. File Activate this radio button to obtain the elevation data from a DEM file. Constant Activate this radio button to use a constant value as the elevation information. Elevation File: Enter the name of a file that contains elevation data. Click the icon to open the File Selector dialog. This option displays when the File radio button is activated. Elevation value: Enter the constant elevation value. This option displays when the Constant radio button is activated. Elevation Units: Click this popup list to select the elevation units used by the DEM or for the constant value. Account for Earth’s curvature Click this checkbox to consider the curvature of the earth in the calculation. This option is recommended if the Geographic (Lat/Lon) is used as the reference projection. Principal Point:

Enter the provided parameters from your camera calibration report.

X: Enter the principal point X coordinate. Y: Enter the principal point Y coordinate. Focal Length: Enter the focal length of the camera. Units: Click this popup list to select the units for principal point and focal length. Number of Iterations: Enter the number of iterations to use for your calculation.

22

Camera Model Properties

Fiducials This tab allows you to customize the fiducials for this geometric correction model. Fiducial Type:

Select the location of the fiducials for this image.

Click this button to use corner fiducials with the image.

Click this button to use side fiducials with the image.

Click this button to use both side and corner fiducials with the image. Viewer Fiducial Locator: Click to open a selection viewer containing the portion of the image around the selected fiducial. Click to change your cursor back to Selection mode. Click to select where to place the fiducial in the selection viewer. Click to unlock the currently selected tool in order to select another tool. Click to lock the currently selected tool for repeated use. Status: Error:

Displays the status of the fiducials calculation. Displays the RMS error of the fiducials calculation.

☞ Make sure the RMS errors are less than 0.5 pixels. If 0.5 pixels are exceeded, double-check the measurements.

Orientation This tab allows you to customize the orientation of this geometric correction model.

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Camera Model Properties Rotation Angle: Allows you to customize the Omega, Phi, and Kappa rotation angles of the image to determine the viewing direction of the camera. Unknown Select when the rotation angle is unknown. Estimated Select when estimating the rotation angle. Fixed Select when rotation angle is defined. Omega: Phi:

Omega rotation angle is roll: around the x axis of the ground system.

Phi rotation angle is pitch: around the rotated y axis (after Omega rotation).

Kappa:

Kappa rotation angle is yaw: around the z axis rotated by Omega and Phi.

Perspective Center Position: coordinates.

Allows you to enter the perspective center in ground

Unknown Select when the ground coordinate is unknown. Estimated Select when estimating the ground coordinate. Fixed Select when ground coordinate is defined. X: Enter the X coordinate of the perspective center. Y: Enter the Y coordinate of the perspective center. Z: Enter the Z coordinate of the perspective center.

Projection This tab allows you to customize the projection of this geometric correction model. Current Reference Map Projection: Displays the current projection status of the image in the Viewer. Projection: Spheroid:

Displays the type of projection of the image in the Viewer. Displays the type of spheroid model of the image in the Viewer.

Zone Number: If applicable, displays the zone number of the image displayed in the Viewer. Datum:

Displays the type of datum of the image in the Viewer.

Map Units: Click this popup list to select the map units for the image in the Viewer.

24

Camera Model Properties Add/Change Projection... Click this button to open the Projection Chooser dialog. From this dialog you can select different types of Projections, Spheroid Models, Zone Numbers and Datum for the image displayed in the Viewer. Set Projection from GCP Tool... SetUp dialog.

Click this button to open the GCP Tool Reference

Apply Click to accept these properties and proceed. Reset Click to reset to the previously applied or solved properties. Save Click to save the camera model to a disk. Save As Click to save to disk as new file. Close Click to cancel these properties and close this dialog. Help Click to view this On-Line Help document. Status: Displays the status of the calculation for this camera correction model.

25

Change DEM Source for Camera model

Change DEM Source for Camera model This dialog allows you to change the elevation file used for geometric model calibration. To open this dialog, start with a calibrated image in the Viewer. Click the icon on the Viewer toolbar menu. From the Image Info dialog, select Edit | Change Map Model... to open this dialog.

Old Elevation File: Displays name of file used to orthorectify the image. New Elevation File: Enter the new location of the elevation file for calibration. The icon opens the File Selector dialog.

OK Click this button to confirm changes and close this dialog. Cancel Click this button to cancel changes and close this dialog. Help Click to open this On-Line Help document.

26

Landsat Model Properties

Landsat Model Properties This dialog allows you to create a custom geometric correction model for the Landsat sensor. This dialog opens when you click OK after selecting the Landsat geometric model in the Set Geometric Model dialog. The Landsat model is for ortho-rectification of any Landsat image which uses TM or MSS as its sensor. The model is derived by space resection based on colinearity equations. The elevation information is required in the model for removing relief displacement.

Parameters This tab allows you to customize basic information about this geometric correction model. Sensor:

Allows you to select the sensor data type to use for your image.

Type: Select the best Landsat sensor type to use with your image. TM Click this radio button to select TM data for the Landsat sensor type. MSS Click this radio button to select MSS data for the Landsat sensor type. Landsat number: Enter the number of the Landsat satellite used for your image. Scene coverage: Allows you to select the amount of your image to use for this Landsat model. Size:

Select the size of the scene to be covered.

Full scene

Click this radio button to select full scene coverage.

Quarter scene

Click this radio button to select quarter scene coverage.

Quadrant: Select the quadrant of the scene to be covered. These options are only enabled when the Quarter scene radio button is activated. NW

Click this radio button to select the northwest quadrant.

NE

Click this radio button to select the northeast quadrant.

SW

Click this radio button to select the southwest quadrant.

SE

Click this radio button to select the southeast quadrant.

Elevation Source:

Select the source of the elevation information for this image.

Use: Select whether to use DEM data or a constant value as the elevation.When the terrain of the rectified area is relatively flat, a constant elevation could be sufficient for an accurate ortho-rectification.

27

Landsat Model Properties File Activate this radio button to obtain the elevation data from a DEM file. Constant Activate this radio button to use a constant value as the elevation information. Elevation File: Enter the name of a file that contains elevation data. Click the icon to open the File Selector dialog. This option displays when the File radio button is activated. Elevation value: Enter the constant elevation value. This option displays when the Constant radio button is activated. Elevation Units: Click this popup list to select the elevation units used by the DEM or for the constant value. Account for Earth's curvature Click this checkbox to consider the curvature of the earth in the calculation. It is not recommended to use this option for Landsat data unless the Geographic (Lat/Lon) is used as the reference projection, because most Landsat data has been systematically connected. Number of Iterations: Enter the number of iterations to use for your calculation. Background: Allows you to enter the value to use for the background of the image in the Viewer, and is used to search the image corners. Value: Enter the background value of the pixels in the image. in Layer: Enter the layer number to use to check for the background value of the image.

Projection This tab allows you to customize the projection of this geometric correction model Current Reference Map Projection: of the image in the Viewer. Projection: Spheroid:

This dialog displays the current projection status

Displays the type of projection of the image in the Viewer. Displays the type of spheroid model of the image in the Viewer.

Zone Number: If applicable, displays the zone number of the image displayed in the Viewer. Datum:

Displays the type of datum of the image in the Viewer.

Map Units: Click this popup list to select the map units for the image in the Viewer.

28

Landsat Model Properties Add/Change Projection... Click this button to open the Projection Chooser dialog. From this dialog you can select different types of Projections, Spheroid Models, Zone Numbers and Datum for the image displayed in the Viewer. Set Projection from GCP Tool... SetUp dialog.

Click this button to open the GCP Tool Reference

Apply Click to accept these properties and proceed. Reset Click to reset to the previously applied or solved properties. Save Click to save the Landsat model to a disk. Save As Click to save the Landsat model to disk as a new file. Close Click to cancel these properties and close this dialog. Help Click to view this On-Line Help document. Status: Displays the status of the calculation for this Landsat model.

29

Change DEM Source for Landsat model

Change DEM Source for Landsat model This dialog allows you to change the elevation file used for geometric model calibration. To open this dialog, start with a calibrated image in the Viewer. Click the icon on the Viewer toolbar menu. From the Image Info dialog, select Edit | Change Map Model... to open this dialog.

Old Elevation File: Displays name of file used to orthorectify the image. New Elevation File: Enter the new location of the elevation file for calibration. OK Click this button to confirm changes and close this dialog. Cancel Click this button to cancel changes and close this dialog. Help

Click to open this On-Line Help document.

30

Polynomial Model Properties

Polynomial Model Properties This dialog allows you to create a custom geometric correction model for polynomial calculations. This dialog opens when you click OK after selecting the Polynomial geometric model in the Set Geometric Model dialog.

Parameters This tab allows you to customize basic information about this geometric correction model. Polynomial Order: Enter the polynomial order to use for the image. A first order polynomial is normally suitable for a transformation between two near recti-linear map systems. Raw satellite imagery can usually be transformed into a projection, such as UTM or State Plane using first order polynomials. Second order polynomials may be necessary for mapping between recti-linear and angular systems. (e.g., Lat/Lon.) Load CFF File Click this button to use an existing .cff file as the transformation coefficients for this model. The Load CFF File dialog opens. CFF files are obsolete in ERDAS IMAGINE, but are loadable to provide backward compatibility with ERDAS 7.x software.

Transformation A CellArray showing the transformation coefficients table is displayed in this tab. These are filled in when the model is solved.

Projection This tab allows you to define the projection of this geometric correction model output map system. Current Reference Map Projection: Displays the current projection status of the image in the Viewer. Projection: Spheroid:

Displays the type of projection of the image in the Viewer. Displays the type of spheroid model of the image in the Viewer.

Zone Number: If applicable, displays the zone number of the image displayed in the Viewer. Datum:

Displays the type of datum of the image in the Viewer.

Map Units: Click this popup list to select the map units for the image in the Viewer. Add/Change Projection... Click this button to open the Projection Chooser dialog. From this dialog you can select different types of Projections, Spheroid Models, Zone Numbers and Datum for the image displayed in the Viewer.

31

Polynomial Model Properties Set Projection from GCP Tool... Click this button to proceed to the GCP Tool Reference SetUp dialog which sets up the projection based on the reference GCPs to be selected.

Apply Click to accept these properties and proceed. Reset Click to reset to previously applied or solved properties. Save Click to save the polynomial model to a disk. Save As Click to save to disk a polynomial model as a new file. Close Click to cancel these properties and close this dialog. Closing the geometric model properties in an unsolved state without the GCP Tool Reference SetUp dialog already displayed automatically starts the GCP Tool Reference SetUp dialog.

Help Click to view this On-Line Help document. Status: Displays the status of the calculation for this polynomial model.

32

Load CFF File

Load CFF File WINDOWS Only This dialog allows you to open an already existing .cff file to use as the transformation coefficients for your polynomial model. This dialog opens when you click the Load CFF File button on the Polynomial Model Properties dialog.

CFF File: Enter the name of the existing .cff file to use for the polynomial model. Click the icon to open a new File Selector dialog.

Ok Click to confirm file selection and close the Load CFF File dialog. Cancel Click to cancel file selection and close the Load CFF dialog. Help Click to open this On-line Help document.

33

Reprojection Model Properties

Reprojection Model Properties This dialog allows you to take a projected image in a map coordinate system and reproject it to another map coordinate system. Refer to the Reprojection Grid discussion under Transformation Matrix. To open this dialog, select Raster | Geometric Correction... from the Viewer menu. From the Set Geometric Model dialog, select Reproject.

Parameters This tab allows you to customize basic information about this geometric correction model. Polynomial Order: Enter the polynomial order to use for the image. A first order polynomial may be adequate for transformation between recti-linear map projections, but transforming to or from Lat/Lon normally requires a second order polynomial. Grid Sampling X: Enter the grid sampling rate for X. Grid Sampling Y: Enter the grid sampling rate for Y.

➲ Grid Sampling Grid Sampling determines the number of equally spaced samples to use (for X and Y) to complete the polynomial approximation of the projection transform. For normal map projection transforms, 8 to16 samples for X and Y are adequate. RMS Error: calculated. X:

Displays the root mean square error. This information is automatically

The X value of the RMS error.

Y: The Y value of the RMS error. Total:

The total value of the RMS error.

Projection This tab allows you to set the output projection of this geometric correction model. Current Reference Map Projection: of the image in the Viewer. Projection: Spheroid:

This dialog displays the current projection status

Displays the type of projection of the image in the Viewer. Displays the type of spheroid model of the image in the Viewer.

Zone Number: If applicable, displays the zone number of the image displayed in the Viewer. Datum:

Displays the type of datum of the image in the Viewer.

34

Reprojection Model Properties Map Units: Click this popup list to select the map units for the image in the Viewer. Add/Change Projection... Click this button to open the Projection Chooser dialog. From this dialog you can select different types of Projections, Spheroid Models, Zone Numbers and Datum for the image displayed in the Viewer.

Apply Click to accept these properties and proceed. Reset Click to reset to previously applied or solved properties. Save Click to save a reproject model to disk. Save As Click to save to disk a reproject model as new file. Close Click to cancel these properties and close this dialog. Help Click to view this On-Line Help document.

35

Rubber Sheet Model Properties

Rubber Sheet Model Properties This dialog allows you to create a custom geometric correction model for rubber sheet calculations. This dialog opens when you click OK after selecting the Rubber Sheeting geometric model in the Set Geometric Model dialog. The rubber sheeting model is a piecewise polynomial method for geometric correction. After a triangulated irregular network (TIN) is formed over all the control points, the image area covered by each triangle in the network is rectified by the first (linear) or fifth (nonlinear) order polynomials. Whether or not to rectify the areas outside the convex hull of TIN is determined by the preference under GCP Editor. It is not recommended to rectify the outside areas because of geometric uncertainty. This model should be used only when:

♦ the geometric distortion is severe ♦ GCPs are abundant ♦ no other geometric model is applicable Parameters This tab allows you to customize basic information about this geometric correction model. Method: Select the best method for calculating your model. Linear Click this radio button to use the linear rubber sheeting, which applies the first order polynomials for each triangle area. Nonlinear Click this radio button to use the nonlinear rubber sheeting, which applies the fifth order polynomials for the rectification of each triangle area, even though it is the nonlinear method.

Projection This tab allows you to customize the projection of this geometric correction model. Current Reference Map Projection: of the image in the Viewer. Projection: Spheroid:

This dialog displays the current projection status

Displays the type of projection of the image in the Viewer. Displays the type of spheroid model of the image in the Viewer.

Zone Number: If applicable, displays the zone number of the image displayed in the Viewer. Datum:

Displays the type of datum of the image in the Viewer.

Map Units: Click this popup list to select the map units for the image in the Viewer.

36

Rubber Sheet Model Properties Add/Change Projection... Click this button to open the Projection Chooser dialog. From this dialog you can select different types of Projections, Spheroid Models, Zone Numbers and Datum for the image displayed in the Viewer. Set Projection from GCP Tool... SetUp dialog.

Click this button to open the GCP Tool Reference

Apply Click to accept these properties and proceed. Reset Click to reset to the previously applied or solved properties. Save Click to save the rubber sheet model to a disk. Save As Click to save the rubber sheet model to disk as a new file. Close Click to cancel these properties and close this dialog. Help Click to view this On-line Help document. Status: Displays the status of the calculation for this rubber sheeting correction model.

37

Spot Model Properties

Spot Model Properties This dialog allows you to create a custom geometric correction model for one of the SPOT sensors. This dialog opens when you click OK after selecting the Spot geometric model in the Set Geometric Model dialog. The Spot model is for ortho-rectification of any image which uses SPOT PAN or XS pushbroom as its sensor. The model is derived by space resection based on colinearity equations. The elevation information is required in the model for removing relief displacement. For ortho-rectifying multiple SPOT or pushbroom images in a single block, please see IMAGINE OrthoBASE.

Parameters This tab allows you to customize basic information about this geometric correction model. Sensor:

Allows you to select the sensor data type to use for your image.

Type: Select the best SPOT sensor type to use with your image. XS Click this radio button to select the color XS sensor. PAN Click this radio button to select the PAN sensor. Elevation Source:

Select the source of the elevation information for this image.

Use: Select whether to use DEM data or a constant value as the elevation. When the terrain of the rectified area is relatively flat, a constant elevation could be sufficient for an accurate ortho-rectification. File Activate this radio button to obtain the elevation data from a DEM file. Constant Activate this radio button to use a constant value as the elevation information. Elevation File: Enter the name of a file that contains elevation data. Click the icon to open the File Selector dialog. This option displays when the File radio button is activated. Elevation value: Enter the constant elevation value. This option displays when the Constant radio button is activated. Elevation Units: Click this popup list to select the elevation units used by the DEM or for the constant value. Account for Earth’s curvature Click this checkbox to consider the curvature of the earth in the calculation. It is recommended SPOT data be used with this option. Number of Iterations: Enter the number of iterations to use for your calculation. 38

Spot Model Properties Background: Allows you to enter the value to use for the background of the image in the Viewer. This is used to search the image corners when no header information is found in the SPOT image. Value: Enter the background value of the pixels in the image. in Layer: Enter the layer number to use to check for the background value of the image. Incidence Angle: Enter the Incidence Angle of the sensor.The Incidence Angle is supplied as (L) left or (R) right by the SPOT data receiving station. Input the Incidence Angle by entering Negative for (L), and Positive for (R).

Projection This tab allows you to customize the projection of this geometric correction model. Current Reference Map Projection: of the image in the Viewer. Projection: Spheroid:

This dialog displays the current projection status

Displays the type of projection of the image in the Viewer. Displays the type of spheroid model of the image in the Viewer.

Zone Number: If applicable, displays the zone number of the image displayed in the Viewer. Datum:

Displays the type of datum of the image in the Viewer.

Map Units: Click this popup list to select the map units for the image in the Viewer. Add/Change Projection... Click this button to open the Projection Chooser dialog. From this dialog you can select different types of Projections, Spheroid Models, Zone Numbers and Datum for the image displayed in the Viewer. Set Projection from GCP Tool... SetUp dialog.

Click this button to open the GCP Tool Reference

Apply Click to accept these properties and proceed. Reset Click to reset to the previously applied or solved properties. Save Click to save a spot model to a disk. Save As Click to save a spot model to disk as a new file. Close Click to cancel these properties and close this dialog.

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Spot Model Properties

Help Click to view this On-Line Help document. Status: Displays the status of the calculation for this spot correction model.

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Change DEM Source for Spot model

Change DEM Source for Spot model This dialog allows you to change the elevation file used for geometric model calibration. To open this dialog, start with a calibrated image in the Viewer. Click the icon on the Viewer toolbar menu. From the Image Info dialog, select Edit | Change Map Model... to open this dialog.

Old Elevation File: Displays name of file used to orthorectify the image. New Elevation File: Enter the new location of the elevation file for calibration. OK Click this button to confirm changes and close this dialog. Cancel Click this button to cancel changes and close this dialog. Help Click to view this On-line Help document.

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Geometric Correction Tools

Geometric Correction Tools The Geo Correction Tools dialog enables you to access four functions: model properties, GCP editing, image resampling, and image calibration. These functions will assist you in the image rectification process. This dialog is opened when you select any option from the Set Geometric Model dialog and click OK.

Click to open the Model Properties dialog for the model you are using with your image. From this dialog, you can specify changes to the model properties displayed for the image in the Viewer.

Click to start the GCP Tool. From the GCP Tool, you can collect GCPs in pairwise mode to be used in the computation of the solution of the geometric model. GCPs are collected for the image in the Viewer and for:

♦ a raster layer in another Viewer, ♦ a map on a digitizing tablet, ♦ coordinates that you enter from the keyboard.

Click to open the Resample dialog. From this dialog, you can choose the desired output file, resample method, and output information.

Click to calibrate the image.

Exit Click to exit close the Geometric Correction Tool dialog. Help Click to view this On-Line Help document.

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Calibrate Image

Calibrate Image This dialog is a warning that alerts you that calibrating the image will cause the Geometric Correction Tools dialog to close, and the current image in the Viewer to be replaced by the

calibrated image. It is displayed when you click the Tools dialog.

icon in the Geometric Correction

Performing image calibration will terminate the Geo Correction Tools and redisplay the calibrated image.

OK Click to confirm that you are aware of the warning statement and wish to continue with the image calibration process. The dialog will close. Cancel Click to cancel the image calibration process and close this dialog. Help Click to view this On-line Help document. ➲ For more information on calibration, see Calibration.

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GCP Tool Reference Setup

GCP Tool Reference Setup This dialog allows you to specify the source from which to collect reference points. The dialog opens when you click the

icon in the Geometric Correction Tools dialog.

Collect Reference Points From: Select one of the following sources from which to collect reference points. Existing Viewer Click to collect reference points from the existing Viewer. The reference map projection is initially set to the map projection of the Viewer. Image Layer (New Viewer) new Viewer.

Click to collect reference points from an image layer in a

Vector Layer (New Viewer) Click to collect reference points from a vector layer in a new Viewer. Annotation Layer (New Viewer) layer in a new Viewer.

Click to collect reference points from an annotation

GCP File (.gcc) Click to collect reference points from a GCP file. GCPs can be saved to and loaded from a .gcc file. This file contains the map and projection information associated with the GCP coordinates. When you select this option and click OK, a file selector opens in which you specify the existing .gcc file. ASCII File Click to collect reference points from an ASCII file. ASCII points may be used as reference to allow the ingestion of GPS data. The standard ERDAS IMAGINE interface is used to import the ASCII data. Since the ASCII data does not contain map information, you are required to specify. When you select this option and click OK, a file selector opens in which you specify the existing .txt file.

➲ For more information, see Import Generic ASCII Data. Digitizing Tablet (Current Configuration) digitizing tablet in its current configuration.

Click to collect reference points from a

Digitizing Tablet (New Configuration) Click to collect reference points from a digitizing tablet in a new configuration.

➲ For more information, see the Digitizer Setup. Keyboard Only Click to enter reference points from the keyboard. It only permits reference GCPs to be entered with the keyboard. Therefore, the user is required to specify map information.

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GCP Tool Reference Setup

OK Click to accept your selection and close this dialog. The GCP Tool is displayed. Cancel Click to cancel your selection and close this dialog. Help Click to view the On-Line Help for this dialog.

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Reference Map Projection Options

Reference Map Projection Options This dialog allows you to specify whether to change points in the CellArray or in the new reference source. To open this dialog, select Edit | Reset Reference Source... from the GCP Tool dialog. This opens the GCP Tool Reference Setup dialog. Click the radiobutton to select a GCP file (.gcc) and click OK. This will open the Reference Map Projection Options dialog.

☞ This dialog is opened only when the source image has projection information and the projection of the reference point source is different.

Options Set Reference Map Projection To:

Selcet one of these two options:

New Click on this button to set the reference projection to the new projection, and reproject the existing points. This will change the points displayed in the CellArray. Current Click on this button to keep the reference projection as the current projection, and reproject the new points. This will change the points in the file but not change the display in the CellArray.

New New Reference Map Projection: image in the Viewer. Projection: Spheroid:

Displays the new type of projection of the image in the Viewer. Displays the new type of spheroid model of the image in the Viewer.

Zone Number: in the Viewer. Datum:

This tab displays the new projection status of the

If applicable, displays the new zone number of the image displayed

Displays the new type of datum of the image in the Viewer.

Map Units: Displays the new map units for the image in the Viewer.

Current Current Reference Map Projection: the image in the Viewer. Projection: Spheroid:

This tab displays the current projection status of

Displays the type of projection of the image in the Viewer. Displays the type of spheroid model of the image in the Viewer.

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Reference Map Projection Options Zone Number: If applicable, displays the zone number of the image displayed in the Viewer. Datum:

Displays the type of datum of the image in the Viewer.

Map Units: Displays the map units for the image in the Viewer.

OK Click to accept your selection and close this dialog. Cancel Click to cancel your selection and close this dialog. Help Click to view the on-line help for this dialog.

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GCP Tool

GCP Tool This dialog allows you to collect ground control points (GCPs) for the source image in the Viewer. Corresponding reference points are used to compute transformations in order to resample or calibrate the image. To open this dialog, click OK in the GCP Tool Reference SetUp dialog once you select your reference for GCP points.

File Save Input Click to save the loaded GCPs to a file. By default the GCPs are saved as a node in the image file in the viewer. Save Input As... Click to save the loaded input GCPs to new file. The Save Input .gcc File Selector dialog opens. This allows the GCPs to be saved to a separate .gcc file rather than into the image file. This may be useful if these GCPs have an application other than to the input image. Load Reference... Click to load an existing reference .gcc file into the GCP Tool. The Reference .gcc File Selector dialog opens. Load Input... Click to load an existing input .gcc file into the GCP Tool. The Input .gcc File Selector dialog opens. Loading input GCPs appends the GCPs from the file to the current input list in the GCP Tool. If the map projections are different, the user is prompted to reproject the points. Save Reference Click to save the loaded reference GCPs to a .gcc file. Save Reference As... Click to save the loaded reference GCPs to a new file. The Save Reference GCPs File Selector dialog opens. Close Click to close the GCP Tool dialog.

View View Only Selected GCPs Click to view only the selected GCPs, highlighted in yellow in the GCP Tool CellArray in the viewer. Show Selected GCP in Table Click to show selected GCP in the CellArray. The graphic GCP icons in the viewer may be selected by clicking on them. Click this menu option to highlight these GCPs in the GCP Tool CellArray.

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To select a GCP, click in the Point # column of the CellArray. Arrange Frames on Screen Click to set size and position of GCP frames and Viewers on the screen.

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GCP Tool Tools... Click to display the tool palette. The GCP Tools dialog opens. Start Chip Viewer Click to start Chip Viewer(s) if desired. By default, the chip viewers are started when the GCP Tool is displayed. These can be closed by the user so this option restarts them.

Edit Set Point Type Click to select the type of points to use. GCPs may be designated as control points or check points. Control points are used to calculate the geometric transformation model. Check points are not used in the calculation, but used to independently evaluate the error in the transformation. Control Click radio button to set point type to Control. Check Click radio button to set point type to Check

➲ For both of these, the point type is set for the current selection in the GCP Tool CellArray. Reset Reference Source... Click to change the reference for your GCP points. The GCP Tool Reference SetUp dialog opens. This allows the user to collect reference points from multiple sources. (e.g., a Viewer, a .gcc file, or a digitizing tablet) If a reference map projection conflict occurs, the user is required to select the desired projection. Reference Map Projection... Click to change the reference map projection and units. The Reference Map Information dialog opens. Point Prediction... Click to calculate the transformation of reference points. The GCP Prediction dialog opens. Turning point prediction only works once a valid geometric transform exists. For example, there is already a minimum set of points defined and solved. At this point, the GCP Tool predicts the position corresponding to the GCP using the transform. This does not add any new information to the transform, but is a useful convenience feature to put the corresponding point in its approximate position. Point Matching... Click to compare spectral values. The GCP Matching dialog opens. Point matching has the same requirements as point prediction and also requires the reference be associated with an image. Point matching uses the transformation to predict the corresponding point position, then matches pixel patches in the two images to determine the precise, sub-pixel position where the cross correlation coefficient is maximized.

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GCP Tool

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The GCP Tool has been updated to use a pseudo map coordinate system rather than a file coordinate system of the image when the image is un-georeferenced. The file coordinates for a pixel value in an image are in the Column and Row indices used to locate that value in the raster array of the image. An un-georeferenced image is normally displayed so that the upper left corner of the image represents file coordinate (0,0). The positive Column (X) direction is to the right, and the positive Row (Y) direction is downwards. When using the GCP Tool in early versions of ERDAS IMAGINE (such as V8.2), the coordinates for an un-georeferenced image were reported using the file coordinate system. In ERDAS IMAGINE V8.3 and above, the file coordinate system definition is unchanged (the Inquire Cursor in File coordinate mode reports coordinates with the positive Y direction being downwards from a 0,0 origin at the top left corner of the image), but the GCP Tool now references an image using the pseudo map coordinate system if it is un-georeferenced (or its real map coordinate system if it is georeferenced). In this system, the origin (0,0) is still at the top left of the image, but the positive Y direction is upwards. This change has been made to standardize the coordinate systems used by ERDAS IMAGINE and to provide added functionality (such as being able to specify relative placements for un-georeferenced images by changing the pseudo origin). Consequently, Y coordinates for un-georeferenced images are now negative, since the image rows are, by definition, below the origin of the coordinate system. The use of the pseudo map system by the GCP Tool may cause some problems if you have sets of coordinates referenced in the old manner. For instance, if you have Ground Control Points measured in ERDAS IMAGINE V8.2 as file coordinates, they will no longer be appropriate for use in the ERDAS IMAGINE V8.3 (and above) GCP Tool. This can easily be solved using the Formula capability of the CellArray. Import the coordinates into a CellArray (for instance, the GCP Tool or Coordinate Calculator) and highlight the column representing the Y file coordinates. Right-click the Column header to get the Column Options menu. Select Formula. Specify the formula as: * (-1). The coordinates should now be pseudo map coordinates that may be used in ERDAS IMAGINE V8.3 and above. Similarly, if you have another software package that expects the Y file coordinates to increase positively downwards, use the CellArray Formula option to convert ERDAS IMAGINE V8.3 (and above) pseudo map coordinates to the correct format before exporting them. To do this, use the same formula as above (i.e., * (-1).

Help Help for GCP Tool ...

Click to view this On-line Help document.

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GCP Tool

Click to turn off and on the automatic GCP editing mode. Other icons in the GCP tool bar are also activated when using automatic GCP editing mode. The automatic GCP editing mode turns on all the automated tools at once; point prediction (or point matching if image to image), auto computes for the transform calculation, and viewer to selected point. This also allows the user to quickly gather points, keep the transform calculation current, and always see what is going on in the viewer(s).

Click to solve the geometric model with control points.

Click to set automatic transformation calculation. Automatic transformation calculation recomputes the transformation whenever a GCP is added, deleted, or modified.

Click to compute the error for check points. This does not compute a new transformation, but updates the RMS error fields for the check points as well as the RMS totals.

Click to use the selection cursor to select GCPs in the Viewer.

Click to create new GCPs. The cursor will turn into a cross-hair in the Viewer. This tool must be locked to create GCPs repeatedly without having to click on this again.

Click to lock the tool currently in use.

Click to unlock the tool currently in use. This allows you to enable different tools.

Click to find a selected point in the source image. The Viewer adjusts to display the point. Both the source viewer and chip viewer adjust.

Click to find a selected point in the reference image. The Viewer adjusts to display the point. Both the source viewer and chip viewer adjust.

Click to update Z values for selected GCPs.

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GCP Tool

Click to set automatic Z value updating for all GCPs.

➲ Some geometric models support Z values (elevation) in the calculation. If applicable, these buttons are enabled to allow Z values to be updated for GCPs. The source of the Z values is determined in the geometric model properties box. Normally they are either defined from a Digital Elevation Model (DEM), or are defined as a constant. Updating the Z values causes the GCP tool to reset the Z values for each selected GCP by reacquiring it from its source. Auto Z value updating reacquires the Z value whenever a GCP’s position is modified.

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GCP Matching

GCP Matching This dialog allows you to find a sub pixel position in the corresponding image with the highest correlation coefficient, and create a GCP at that position. To open this dialog, select Edit | Point Matching... in the GCP Tool dialog.

Layers to match: Input Layer: Click this popup list to select your source layer. Image matching is on single layers so the user must select the input layer to match. Generally, results are best if the spectral characteristics of the layer (e.g., wavelength), corresponds with the reference layer to match. Reference Layer: Click this popup list to select your destination layer. Image matching is on single layers so the user must select the input layer to match. Generally, results are best if the spectral characteristics of the layer (e.g., wavelength), corresponds with the layer to match.

Matching Parameters: Max. Search Radius: Enter the maximum radius to search for a match. Search Window Size:

Enter the number of pixels (wide and high) to scan for matches.

X: Enter the window size for X in the number field. Y: Enter the window size in Y in the number field.

Threshold Parameters: Correlation Threshold: Enter the minimum correlation to accept a matched point. If the correlation value, range 0 - 1, is below this threshold, then do not create the corresponding GCP. If it is quarter or equal to this threshold, then create the corresponding GCP. Discard Unmatched Point Click this checkbox to discard a point if it is below the correlation threshold. If the correlation value is less than the correlation threshold, then also delete the user-defined point that failed to match successfully. This allows the user to quickly click on possible GCPs, find a match and keep them if the match is acceptable, but discard them both if the match is acceptable.

Match All/Selected Points: Click on one of the two buttons below to start the matching process.

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GCP Matching Reference from Input Click this button to match reference points from input points. This button matches already existing points in the GCP Tool with its corresponding set of points. Reference from Input adjusts the reference points based on the matching parameters while the input points remain unchanged. Input from Reference Click this button to match input points from reference points. This button matches already existing points in the GCP Tool with its corresponding set of points. Input from Reference is the opposite of Reference from Input.

➲ Both Reference from Input and Input from Reference are useful for fine tuning existing points which were entered manually. These two functions operate on the selected GCPs.

Match Next Click this check box to match points as they are created. This indicates if the matching operation is turned on or off for the next created GCP.

Close Click to close the GCP Matching dialog. Help Click to view this On-Line Help document.

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Nominal Cell Sizes

Nominal Cell Sizes This dialog allows you to recalculate cell sizes with different X and Y defaults. This dialog is opened when you click the Nominal... button in the Resample dialog.

X: Enter the new default X value. Y: Enter the new default Y value. Apply Click to apply the nominal cell sizes to the resample dialog. Close Click to close the Nominal Cell Sizes dialog. Help Click to view this On-Line Help document.

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GCP Prediction

GCP Prediction This dialog calculates the transformation of reference points. To open this dialog, select Edit | Point Prediction... in the GCP Tool dialog.

➲ These options use the current geomodel to compute and predict the corresponding points. Predict All/Selected Points: Click one of the two buttons below to begin the GCP Prediction process. Reference from Input This button predicts reference points from input points. Input from Reference This button predicts input points from reference points.

Predict Next Click this check box to predict points as they are created. Close Click to close the GCP Prediction dialog. Help Click to view this On-Line Help document.

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Recalculate Output Defaults

Recalculate Output Defaults This dialog uses skip factors to calculate the default output size of an image. To open this dialog, click the Recalculate Output Defaults... button in the Resample dialog.

Skip Factors: X: Enter the X skip factor for recalculating output defaults. You cannot enter numbers larger than the size of the image. Y: Enter the Y skip factor for recalculating output defaults. You cannot enter numbers larger than the size of the image.

Recalculate Click to perform a recalculation of the output defaults. Close Click to close this dialog. Help Click to view this On-Line Help document.

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Reference Map Information

Reference Map Information This dialog displays the current map projection information for the image in the Viewer. It also allows you to specify reference points for output map projections. To open this dialog, make your selection in the GCP Tool Reference SetUp dialog, and click OK.

Current Reference Map Projection: Displays the current projection status of the image in the Viewer. Projection:

Shows the type of projection of the image in the Viewer.

Spheroid:

Shows the type of spheroid model of the displayed image.

Zone Number: Viewer. Datum:

If applicable, shows the zone number of the image displayed in the

Shows the type of datum of the displayed image.

Map Units: Click this popup list to change the map units for the image in the Viewer. Add/Change Projection... Click this button to open the Projection Chooser dialog. From this dialog you can select different types of Projections, Spheroid Models, Zone Numbers and Datum for your displayed image.

OK Click to accept your selection and close this dialog. Cancel Click to cancel your selection and close this dialog. Help Click to view this On-Line Help document.

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Resample

Resample This dialog allows you to set the default values to use when resampling the input image. To open this dialog, click the Resample icon (shown below) in the Geometric Correction Tools dialog..

☞ Before the image can be resampled, reference data must be calculated, and models (except for Affine and Reproject) must have a solution or the image must be calibrated.

Output File: Enter the output file name of the resampled image. Resample Method: Select the resampling technique from the popup list. ➲ A description of different resample techniques can be found in ERDAS Field Guide. Output Map Information: This map information is calculated automatically. The output map information options in the Resample dialog are automatically preset with intelligent defaults based on the input image geometry and the geometric model. Projection: Displays the default output map projection type. This is the projection of the reference map system of the geometric model. Units: Displays the default output map units. This is the units of the reference map system of the geometric model. Number rows: Displays the number of rows in the output file. Number columns: Displays the number of columns in the output file.

➲ These are both computed based on the output corners and cell size variables below. Output Corners: ULX: Enter the upper left X coordinate for the resampled image. LRX: Enter the lower right X coordinate for the resampled image. ULY: Enter the upper left Y coordinate for the resampled image. LRY: Enter the lower right Y coordinate for the resampled image.

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Resample

➲ The default output corners are computed fromthe input image and geometric model to resample the entire input image. This is done by transforming the four corners of the input image with the geometric model forward transformation. Note that these corners may not represent the entire input image space when using a non-affine or non-first order polynomial. The option to Recalculate Output Defaults samples a grid of points (rather than just the four corners) to more closely match the entire input image space.

Output Cell Sizes: X: Enter the X cell size for the resampled image. Y: Enter the Y cell size for the resampled image. Nominal... Click to enter the cell sizes as nominal meters. The Nominal Cell Sizes dialog opens.

➲ The output cell sizes have also automatically computed defaults. These are based on an assumption that optimum cell size neither oversamples or undersamples the input image space. For example, the output image extent is approximately the same as the input image. These are only provided as defaults and may not be the desired values in all applications.

Recalculate Output Defaults... Click to reset the output defaults. The Recalculate Output Defaults dialog opens. This may be necessary when using a non-affine or non-first order polynomial. These geometric models may not be able to define the proper output extent using only the four corners of the input image. A grid sampling approach provides a better estimation of the geometrically transformed input image extent.

Ignore Zero in Stats. Click this check box to ignore zero when computing the statistics for the output file.

OK Click to accept your edits and start resampling. Batch Click to place the resampling process in the batch queue. Cancel Click to cancel your edits and close the Resample dialog. Help Click to view this On-Line Help document.

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Warning

Warning This warning dialog indicates that the properties and/or GCPs used to calculate the solution to your model have changed. You are given the option to recompute the solution or delete the current solution.

Recompute Solution Click this radio button to recompute the solution. Delete Current Solution Click this radio button to delete the current solution. OK Click to process your selection and close this warning dialog. Cancel Click to cancel your selection and close this warning dialog. Help Click to view this On-Line Help document.

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GCP Tools

GCP Tools This tool palette allows you to create and select ground control points (GCPs). It is opened when you select View | Tools... from the GCP Tool menu bar.

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While collecting GCPs, if you want to change the band combination you are viewing for the source or destination image, close the magnifier window with the Viewer and use Raster | Band Combinations to change the band combination of the layer. Then, click on the Start GCP Editor icon on the Geo Correction Tool to redisplay the magnifier for this window. Any time you want to open a magnifier Viewer, simply click the View menu, then choose Create Magnifier. A magnifier Viewer is opened in the workspace.

Click to activate the GCP selection tool. This tool allows you to select a GCP symbol displayed in a Viewer by clicking on it. This is the default tool.

Click to activate the GCP creation tool. This tool allows you to create a GCP in a Viewer by positioning the cross hair at the desired location and clicking. To create multiple GCPs, check that the Locked icon is displayed. If the Locked icon is not displayed, click the Unlocked icon.

Click this icon, if displayed, to unlock the currently selected tool. When you click this icon, it is replaced with the Unlocked icon described below. When this icon is displayed, the currently active tool will remain active until another tool is selected.

Click to lock the currently selected tool until another tool is selected. When you click this icon, it is replaced with the Locked icon described above. When this icon is displayed, the currently selected tool is active for a single event only. The default tool then becomes the active selection tool.

Click to see this On-Line Help document.

Close Click to close the GCP tool palette.

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