The Compute Change function computes the differences between two categorical or continuous raster datasets.
Notes
This function can be used to enumerate the differences between two classified rasters for land-cover change analysis, or it can be used to examine changes between two single-band, continuous rasters such as elevation, temperature, canopy cover, and so on.
There are six computation methods:
- Difference—Calculates the mathematical difference (subtraction) between two raster layers.
To Raster - From Raster
- Relative Difference—Calculates the difference between the raster datasets while accounting for the magnitude of the pixel values.
(To Raster - From Raster)/max(From Raster, To Raster)
- Categorical—The difference between two categorical or thematic rasters, where the output shows every class transition that occurred between the two rasters. For example, a class labeled Forest > Developed indicates a change from Forest in From Raster to Developed in To Raster.
- Spectral Euclidean Distance—Calculates the Euclidean distance between two multiband rasters by treating each pixel as a vector. Larger values indicate more change between the images.
- Spectral Angle Difference—Calculates the spectral angle between two multiband rasters by treating each pixel as a vector. Larger angles indicate more change between the images.
- Band With Most Change—Calculates the band that accounts for the most change in each pixel between two multiband rasters.
To visualize only the pixels that changed from one class to another, use the From Classes and To Classes parameters, and check the Changed Pixels Only box. For example, to see only those pixels that changed from Forest to Developed, enter the class value for Forest in the From Class Values parameter, enter the Developed class value in the To Class Values parameter, and check the box to include changed pixels only. Only the pixels that changed from Forest to Developed are symbolized in the output layer. All other pixels are grouped in a class named Other, which is transparent by default.
If Compute Change Method is set to Categorical and one of the inputs is not categorical, a simple difference is calculated.
Note:
When analyzing categorical change, both From Raster and To Raster must have an associated raster attribute table. The attribute table must have either a VALUE field, CLASS_NAME field, CLASSNAME field, or one string field. The data in these fields is used to compare between the two rasters.
Parameters
Parameters for the Compute Change function are detailed below.
Parameter | Description |
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From Raster | The first raster to be used in the computation. To evaluate change from time 1 (earlier) to time 2 (later), enter the time 1 raster. |
To Raster | The second raster to be used in the computation. To evaluate change from time 1 (earlier) to time 2 (later), enter the time 2 raster. |
Compute Change Method | The method used for computation.
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From Class Values | The class values from the From Raster parameter to be included in the computation, if comparing two categorical rasters. This is a space-delimited list of integer values corresponding to the ClassValue field in your input raster dataset. |
To Class Values | The class values from the To Raster parameter to be included in the computation, if comparing two categorical rasters. This is a space-delimited list of integer values corresponding to the ClassValue field in your input raster dataset. |
Field Name For Class Names In From Raster | A field that stores class names in the From Raster input. The tool automatically searches for the ClassName field or Class_Name field to use. Use this option if the input does not contain these standard field names. |
Field Name For Class Names In To Raster | A field that stores class names in the To Raster input. The tool automatically searches for the ClassName field or Class_Name field to use. Use this option if the input does not contain these standard field names. |
Filter Method | Choose the filter method for categorical change computation.
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Define Transition Colors | Specifies the color to use to symbolize the output classes. When a pixel changes from one class type to another, the output pixel color represents the initial class type, the final class type, or a blend of the two.
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Cellsize Type | Choose which cell size to use in the output raster. If all the input cell sizes are the same, all the options will yield the same results.
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Extent Type | Choose which extent should be used in the output raster:
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