This raster question comes up quite a bit on PostGIS mailing lists and stack overflow and the best answer often involves the often forgotten ST_Reclass function that has existed since PostGIS 2.0. People often resort to the much slower though more flexible ST_MapAlgebra or dumping out their rasters as Pixel valued …

I've been asked this question in some shape or form at least 3 times, mostly from people puzzled why they get this error. The last iteration went something like this:

I can't use ST_AsPNG when doing something like

1SELECT ST_AsPNG(rast)
2    FROM  sometable;

Gives error: Warning: pg_query(): Query failed: ERROR: …

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 …

Every one or two months, someone asks on the PostGIS users list usually somewhat panicked, My geometry is missing when I look in pgAdmin III

This is documented in the PostGIS Frequently Asked questions section of the manual I tried to use PgAdmin to view my geometry column and it is blank, what gives?

Since this …