Intro Chapter 5 A

Chapter 5Raster Geoprocessing Prochnow’s GIS

Geoprocessing ►A

collection of spatial analysis functions.

► GIS

tools and processes of creating and modifying geospatial data using operations that have one or more parameters.

► Geoprocessing

is central to GIS because it turns geospatial data into useful spatial information and

Geoprocessing ► Conventionally,

raster and vector geospatial data are processed separately

► Raster

data more often used in spatiotemporal modeling in environmental apps.

► Vector

data used primarily for digital mapping and resource inventories.

Special Features of Raster Geospatial Data ► Raster

data organized into bands, themes, or layers.

► Raster

does not realize discrete features.

► Raster

data sets come in different image depths (per grid cell).   

One Bit: black and white (0 and 1 only) Eight Bits: 256 levels of gray True Color: 256 possible values for blue, green and red each.

Figure 5.1

What is the image depth?

Raster Formats ► Different

methods of compression

► Different

data sources

► Designed

to work with different softwares.

Generic Raster File Formats ► Simplest ► Closest

format.

Format

to conceptual raster data

► Includes

ASCII and IEEE formats, which just use text files to store data

► Can

be used by all raster platforms

Raster Data Interchange Format ► Facilitates ► Includes

sharing of raster data.

TIFF, GEOTIFF and the USGS SDTS (which allows for storage with metadata).

Raster Data Compression Formats ► Less

computer memory (bandwidth) required.

► Uses

wavelet algorithms to decompose rasters.

► Includes ► Have

GIF, JPEG, and MrSID

compression ratios, like 5:1, 10:1, and 50:1, respectfully.

Remote Sensing Image Formats ►

Landsat MSS, Landsat TM, and SPOT images are stored using one of three binary formats.  Band Sequential: Each image band is kept as a separate file.  Band Interleaved by Line: pixels of each band are recorded band by band or each line or row of the image.  Band Interleaved by Pixel: places all the different bands from a single pixel together.

►

Only band sequential usable by GIS and data compression techniques.

►

All formats for a georeferencing header built in.

Figure 5.2

Proprietary Raster Geospatial Data Formats ► Think ► Has

of ArcGIS GRID format

an associated value attribute table (VAT). His enables the use of a database management system to manipulate cell values and to relate the cells to other attributes pertaining to them.

Figure 5.3

Raster Geoprocessing and Digital Image Analysis ► Rater

Processing in GIS Differs from Remote Sensing Image Analysis

► GIS

Raster Processing focuses on the Management and Analysis of Geospatial Data, rather than on the Interpretation of the Images.   

Determine Spatial Relationships Generate New Data Layers Develop Models for Spatial Problem Solving

Advantages and Limitations of Raster GeoProcessing ► Effective

Surfaces

Representation Of Continuous

► Fast

Computer Processing

► Fast

Display Of Surface Data

 Rasters All Have A Common Framework  No Need To Calculate Geometric Intersection, Topological Building, And Error Checking That Are Needed By Vector Overlays.

 No Need For Shading Routines  Can Build “Pyramids” With Raster.

► Ability

to Handle Very Large Databases

► Applications

that are difficult or impossible to perform using vector data.  Hydrologic Modeling  Wildfires  Pollution Dispersion

The Downside of Raster Geoprocessing ► Network

Analysis Impossible

► Not

enough precision for land surveying

► Not

Good for Projects that Rely on Linear Boundaries.