Combine/ Compare Terrain Layers

The Combine/ Compare Terrain Layers command allows the user to generate a new gridded elevation (or other gridded value) layer by combining and/or comparing the elevation values from two other loaded terrain layers.

When selected, the command displays the Combine Terrain Options dialog which allows the user to set up generation of the new terrain layer. Once completed the new terrain layer is added to the Overlay Control Center and displayed.


The Combine Terrain Layers Options panel (displayed above) allows the user to select the name to assign to the newly generated layer, select the layers to combine to make the new layer, select the operation to perform when combining the new layer, and select the vertical units and sample spacing of the new layer.


The available operations are described below:

Select First Elevation Layer(s) to Combine/Compare

From the list of loaded layers select the first elevation layer(s) to be used in the operation.

Select Elevation Layer(s) to Combine the First Layer(s) with

From the list of loaded elevation layers, select the layer(s) to be used in the second half of the operation.

Vertical Units

Specify the output units for the combined elevation grid. The unit interpretation of the input layers is defined in the layer options.


Specify the elevation shader to use for the output layer. This will set a custom shader for the combined terrain layer, unless the Default Shared Shader is selected. Since the combined terrain values typically represent a comparison or difference, in a different numeric range than the original input elevation layers, using an elevation shader specific to the layer can help highlight the number range in the combined elevation grid.

Once the combined elevation grid has been created, the shader setting may be modified in the layer options on the Display tab.

Sample Spacing

The Sample Spacing section allows the user to select the grid spacing to use when generating the file. The default value is the average of the grid spacings of all the currently loaded raster and elevation overlays.

If the Always Generate Square Pixels option is checked, the smaller of the specified x and y resolutions will be used for both the x and y resolution.

Selecting Always Generate Square Pixels ensures that the resultant image file will look good even in software that is not able to deal with pixels that aren't square.

To specify the spacing in units other than those of the currently selected view/ export projection, press the Click Here to Calculate Spacing in Other Units button.

Compare Value

Specify the compare value when using an operation that references a compare value: