Envi Reader User Guide

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ENVI Reader for ArcGIS® User’s Guide The following constitutes the User’s Guide for version 1.0 of the ENVI Reader for ArcGIS.

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Usage Information . . . . . . . . . . . . . . . . . . . . . 3

Frequently Asked Questions . . . . . . . . . . . . 6 Reporting Problems . . . . . . . . . . . . . . . . . . . 9

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ENVI Reader for ArcGIS® User’s Guide

Installation The installation program is distributed on the RSI web site at http://www.rsinc.com/envi. Begin the installation by double-clicking on the installer executable. Additional download and installation instructions are available on the web site with the installation program. Note If ArcGIS 8.1 or higher is not installed or cannot be found by the installation program, the installation will exit without completing.

Required Features The required features in the installation program include the main program files, documentation files, and sample data. The software application file must be installed to a location determined by the existing ArcGIS installation. The documents included in the installation are the Release Notes text file, this User’s Guide, the end-user license agreement which you must agree to before installing the software, and three sample raster datasets in ENVI format.

Verifying Installation After installation, check to verify that the plug-in was installed correctly. This can be accomplished by starting ArcMap™, then selecting Tools → Options from the main menu. Click the Raster tab. In the Raster Format Browsing section, scroll to the bottom of the list. If the last (or close to last) entry in the list says, ENVI Raster Format *.dat, the installation has been successful; otherwise, the installation has failed and must be corrected before proceeding. The sample data can be viewed for further verification that this module was correctly installed.

Installation

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Usage Information Use ENVI format raster data to query, preview, and manage using ArcCatalog™; to visualize using ArcMap; and to analyze using Spatial Analyst™. ENVI format raster datasets can be used the same as other raster data formats supported in ArcGIS.

ENVI Header Keywords Many of the keywords written in ENVI raster dataset headers can or must be used in order to correctly use the dataset in the ArcGIS environment. Other keywords either cannot be utilized in this environment or signify that the dataset itself cannot be used. The following keywords are read in from ENVI File Headers and utilized in the ArcGIS environment. Samples (required) The number of columns of raster data in the dataset. Lines (required) The number of rows of raster data in the dataset. Bands (required) The number of bands of raster data in the dataset. Interleave (required) The order the pixels are arranged in the raster dataset. Data Type (required) Data type of each pixel value in the dataset. Supported types: 8 bit unsigned integer, 16 and 32 bit signed and unsigned integer, 32 and 64 bit IEEE floating point. Unsupported types: Single and double precision complex, signed and unsigned 64 bit integer. Header Offset (optional) The number of bytes into the file where the raster data begins. Typically 0. ByteOrder (optional) Set to 1 for data files requiring data to be byte swapped to be used on Intel/Motorola hardware. Classes (optional) Number of classes contained in a classification result. Class Names (optional) Names of the classes in the classification result. This keyword is ignored if Classes is not set. Class Lookup (optional) Colormap lookup table used to map classes in a classification result to a specific color for display. This keyword is ignored if Classes is not set. Band Names (optional) Default name for each band in the dataset.

Usage Information

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Wavelength (optional) Wavelengths are not directly supported in the ArcGIS framework, so they are appended to the band name, or used if no band name is present. Wavelength Units (optional) If wavelength information is also present, the wavelength units will be appended to the wavelength in the band name. Pixel Size (optional) The cell size of pixels in this dataset. Only used if map info is not present. Map Info (optional) Determines the coordinates of the upper left corner and the pixel size. If the map info includes projection information, this will be imported if it can be converted into the projection representation required by ArcGIS. Currently, projection information can only be converted for Geographic, UTM, US State Plane, Map Grid of Australia, and Australian Map Grid. Data Ignore Value (optional) The value of NODATA in this dataset. The following list of header keywords are those which will trigger an ENVI Format raster dataset to be unusable in ArcGIS. Read Procedures — Datasets which are not using the default read procedure cannot be interpreted using this module. File Type — Spectral Libraries, ENVI Meta Files, or ENVI Virtual Mosaics, cannot be interpreted using this module. File Compression — Files compressed using the IDL internal compression mechanism cannot be interpreted using this module.

ENVI Statistics Files ENVI format raster datasets may have associated statistics files that contain statistical information for each band in a raster dataset. If present, these files will be read and used to provide image statistics to ArcGIS. The statistics in ArcGIS are used to provide enhanced default rendering for initial display of raster data. The statistics that will be read and returned are minimum, maximum, mean, and standard deviation.

Raster Format Browsing To speed browsing, raster datasets are identified in ArcGIS by their file extension. This is acceptable for most formats; however, ENVI raster datasets are not constrained to any specific extension or even any extension at all. This can present unique problems for users who are used to required file extensions. By default, ArcGIS identifies any image with the extension .img, .bil, .bip, .bsq, and .raw, Usage Information

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as these extensions are associated with other formats. The extension .dat is added to this list when the plug-in is installed, so files with this extension will also be identified. Users with any of these extensions for their data filenames will automatically find their data. However, datasets with different extensions or no extension will not automatically appear in the Add Data browser or in ArcCatalog without customizing. This behavior can be modified in the Raster Format Browsing section of the Raster tab in the Tools → Options dialog. If one or only a few different file extensions are used, they can be added to the browse list by scrolling to the bottom of the browse table to the format named ENVI Raster Format. Clicking in the File Extensions portion of this list allows the user to enter the additional extensions to use to find their files. A comma-delimited list of these expressions is allowed. For example, if the file extensions .dat and .int are expected, the expression *.dat, *.int will force all of these files to be shown in the browser. For files that do not have extensions or situations where many different extensions are impractical to manage in the browse list, you must click on Search All Files to find valid raster formats (may be slow) and use the slow browse mode. This option forces all files in the directory to be passed to all available format DLLs in an attempt to recognize the raster format files. When there are many files in a directory, this method can be slow; however, it is the only way for ArcGIS to identify all raster datasets, including those with no extension.

Usage Information

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Frequently Asked Questions Why can’t I find my ENVI format raster dataset in ArcCatalog or the ArcMap Add Data dialog? The most likely cause of this problem is that ArcGIS is not properly configured to look for your data files. If your data filenames do not have an extension, or use a nonstandard extension, ArcGIS will not, by default, be able to identify your files as raster datasets. See the Raster Format Browsing notes in the Usage Information section of this document for instructions on how to properly configure ArcGIS to identify your files.

Why does my data initially appear as a black or gray rectangle? This will occur if the image does not contain statistics, and these must be calculated for the image to be properly stretched for display. Users with the ENVI software package can compute statistics files for their data in ENVI that will be automatically recognized when the data is added to ArcGIS. The ENVI statistics file must reside in the same directory as the dataset. Alternatively, statistics can be calculated on the fly in ArcMap that will be used for the duration of the session before being discarded, or persistent statistics can be calculated using ArcCatalog. To compute statistics on the fly in ArcMap, do the following: 1. Right click on the raster layer in the Table of Contents. 2. Select the Properties option from the context menu, then click on the Symbology tab in the Properties sheet for the raster layer. Make sure that RGB composite (for multiple band images) or Stretched (for single band images) is selected in the upper left corner Show: list. 3. In the Stretch frame, select the Type drop-down list (default None) and select the Standard Deviation option. This is similar to, although not exactly the same as, the 2% stretch in ENVI. Click OK. 4. If this is a large image, it may take a few moments for the automatic statistics calculation to take place and you may see a progress bar appear in the status bar at the bottom of ArcMap while this occurs. 5. The image should now be stretched and should nearly (though perhaps not exactly, due to a slightly different stretch algorithm), resemble the default display of the image in ENVI. To compute persistent statistics in ArcCatalog do the following:

Frequently Asked Questions

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1. Right click the raster dataset in the browser window. 2. Select Calculate Statistics on the context menu, then select any desired skip factors or ignore value. Click OK to begin statistics calculation. 3. The statistics are stored in the auxiliary file associated with the dataset so ArcGIS will be able to read them as needed in the future. Note These statistics cannot be imported into ENVI.

Why do I receive an “Invalid Raster Dataset” error when I try to use my ENVI format raster dataset? The most likely reason for this error is that your raster dataset uses some ENVI features that make this data unusable within the ArcGIS environment. See the ENVI Header Keywords notes in the Usage Information section above for details on what header keywords force a file to be unrecognized. Alternatively, if the size of the data file is not consistent with the expected size of the dataset (header offset + rows * columns * bands * pixel depth), the file will be considered invalid.

Why doesn’t ArcGIS recognize the projection information from my ENVI format raster dataset? Your data probably uses a projection that cannot be read directly from the ENVI header. The list of supported projections is detailed with the map info keyword in the ENVI Header Keywords section of this document. If your projection is unsupported, you will have to manually set the projection associated with this raster dataset in ArcGIS. This operation is performed using ArcCatalog as follows: 1. Right click on the desired ENVI format raster dataset in the browse window. 2. Select the Properties option from the context menu, then click the Spatial Reference tab in Property sheet that appears. The projection information should be displayed in the projection frame. If the correct projection does not appear here, click the Edit button to change the projection associated with this dataset. You may select, import, define, or create a new projection to associate with your data here. For more information on setting the projection in this manner, consult the ArcGIS documentation. Click OK on the projection definition dialog when complete, then click OK to exit the property sheet and apply the changes.

Frequently Asked Questions

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3. The projection information is stored in the auxiliary file associated with the dataset so ArcGIS will be able to read them as needed in the future. Note Any changes made to the projection definition of a dataset in this manner cannot be imported into ENVI.

What is the .aux file that appears with the same root filename as my ENVI format raster dataset after using the data in ArcGIS? The .aux, or auxiliary file, created by ArcGIS for raster datasets may contain a variety of information that cannot or is not supported for a specific raster format or dataset. For example, the JPEG format does not allow support for projection information, so if georeferencing information is desired for a JPEG file, this can be stored in an auxiliary file. When a raster dataset is first opened, an auxiliary file containing a minimal set of information about the file is created. This file can be used to store any additional information about a raster dataset (for example statistics for an ENVI format raster dataset that does not have an ENVI statistics file). This can be useful in many situations, but if changes are made to a raster dataset in a different software environment, the auxiliary file can become obsolete, resulting in poor display. In extreme cases, the dataset may become unusable. If you are having trouble with raster data that previously behaved normally, this association can be the problem. It is generally safe to delete the auxiliary file, although you will lose any information (for ENVI raster datasets, this will most commonly be statistics or projection) contained in the file.

Why aren’t changes I make to my ENVI format raster dataset in ArcGIS recognized in ENVI? Because the ENVI Raster Format DLL For ArcGIS provides only read access to ENVI data in the ArcGIS environment, any changes made to ENVI data in this environment cannot be written directly to the ENVI raster dataset. These changes are stored in the auxiliary file for the raster discussed above. Changes made in the auxiliary file are accessible from with ArcGIS, but cannot be used in the ENVI environment. Therefore, any modifications made to an ENVI dataset in ArcGIS will only be usable in the ArcGIS environment.

Frequently Asked Questions

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Reporting Problems Before reporting a problem, please review this documentation and check the web site for software updates and new information. Your comments and suggestions will help us improve this product. Any problems that you encounter in using this product should be sent to [email protected]. The subject field of your e-mail should be informative but brief. For example, “ENVI Reader for ArcGIS georeferencing problem” is a short, but descriptive subject line entry. The following are guidelines for the information to include in your problem report: 1. The product name. 2. The version number. 3. Your hardware and operating system. 4. A description of the problem encountered. 5. A reproducible test case that illustrates the problem. 6. The specific text of any error messages encountered. 7. Any sample data (JPEGs for error snapshots, small data files, etc.). 8. Any attempted workarounds or preliminary analysis of the nature of the problem.

Reporting Problems

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Reporting Problems

ENVI Reader for ArcGIS® User’s Guide