Executing DEM operations

PostGIS comes with several functions for use on digital elevation model (DEM) rasters to solve terrain-related problems. Though these problems have historically been in the hydrology domain, they can now be found elsewhere, for example, finding the most fuel-efficient route from point A to point B or determining the best location on a roof for a solar panel. PostGIS 2.0 introduced ST_Slope(), ST_Aspect(), and ST_HillShade() while PostGIS 2.1 added the new functions ST_TRI(), ST_TPI(), and ST_Roughness(), and new variants of existing elevation functions.

Getting ready

We will use the SRTM raster, loaded as 100 x 100 tiles, in this chapter's first recipe. With it, we will generate slope and hillshade rasters using San Francisco as our area of interest.

The two queries below use variants of ST_Slope() and ST_HillShade() that are only available in PostGIS 2.1 or higher versions. The new variants permit the specification of a custom extent to constrain the processing area...