Posts tagged with 'ST_Value'

Getting distinct pixel values and pixel value counts of a raster

PostGIS raster has so so many functions and probably at least 10 ways of doing something some much much slower than others. Suppose you have a raster, or you have a raster area of interest — say elevation raster for example, and you want to know the distinct pixel values in the area. The temptation is to reach for ST_Value function in raster, but there is a much much more efficient function to use, and that is the ST_ValueCount function.

ST_ValueCount function is one of many statistical raster functions available with PostGIS 2.0+. It is a set returning function that returns 2 values for each row: a pixel value (value), and a count of pixels (count) in the raster that have that value. It also has variants that allow you to filter for certain pixel values.

This tip was prompted by the question on stackexchange How can I extract all distinct values from a PostGIS Raster?

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