Module 9: Rasters

Last week we worked with Vectors, this week we learned how to write scripts for Raster data.  The functions and classes found in the arcpy.sa module are used to list, describe, create, and modify rasters.

ListRaster is used to find out what rasters exist in a workspace - Esri GRID and geodatabase rasters do not have file extensions; .img, .tif, and .jpg are returned for other image formats.

Describe returns general and specific properties of raster datasets.  The elements that can be described are datasets, bands, and catalogs.  Different properties are available depending on which element is being described.

Once a raster object is created, it can be used in other Python statements and map algebra statements.  Properties include band count, cell height and width, spatial reference, pixel type, and more.  The raster object has only one method possible - save.  This is used to make a temporary raster object permanent after ArcMap has closed.

In order to be able to use the tools in the arcpy.sa module directly, all the functions can be imported.  This can be helpful especially when using map algebra operators.

Several classes in the arcpy.sa module were introduced, including Remap and Neighborhood.  There are 8 others.

This week's lab asked us to create a raster from 2 existing rasters: elevation and landcover.  To start, we wrote code to see if the spatial analyst extension was available, then checked out the spatial analyst extension.  Next we reclassified the landcover raster so that 3 forest landcover classifications were changed to 1.  Then we created temporary rasters for elevation that had slope between 5-20 degrees, and aspect between 150-270 degrees.  The combined temporary rasters were saved to a final raster in a newly created geodatabase, and the spatial analyst extension was checked back in.  Below is the result, seen in ArcMap.