Converting between rasters and geometries

In the last recipe, we used the geometries to filter and clip rasters only to the areas of interest. The functions ST_Clip() and ST_Intersects() implicitly converted the geometry before relating it to the raster.

PostGIS provides several functions for converting rasters to geometries. Depending on the function, a pixel can be returned as an area or a point.

PostGIS provides one function for converting geometries to rasters.

Getting ready

In this recipe, we will convert rasters to geometries and geometries to rasters. We will use the ST_DumpAsPolygons() and ST_PixelsAsPolygons() functions to convert rasters to geometries. We will then convert geometries to rasters using ST_AsRaster().

How to do it...

Let's adapt part of the query used in the last recipe to find out the average minimum temperature in San Francisco. We replace ST_SummaryStats() with ST_DumpAsPolygons() and then return the geometries as WKT.

WITH geoms AS (
        SELECT
                ST_DumpAsPolygons...