Hello, I am fairly new to using rasters in postgis, but I am wondering if there is a faster way to extract values from categorical rasters (e.g. landcover types) than using map algebra. In the PostGIS in Action book, pg 404 has a function called ST_SelectByValue(raster|geometry, 'expression') which seems to incorporate map algebra, however I can't seem to tell if this function is finished and available in postgis as I get an unknown function error.
My version is this. "PostgreSQL 9.3.2 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3, 64-bit POSTGIS="2.1.1 r12113" GEOS="3.3.3-CAPI-1.7.4" PROJ="Rel. 4.7.1, 23 September 2009" GDAL="GDAL 1.9.0, released 2011/12/29" LIBXML="2.7.8" LIBJSON="UN (...)" And I found a webpage http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking03 search for "ST_SelectByValue" at the bottom, indicating that it was finished. AAccomplished Objectives <http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking03#AccomplishedObjectives> *ST_ValueCount(raster, value) -> integer - done see below* *ST_ValuePercent(raster, value) -> double precision - done see below* *ST_Resample(raster, method, originx, originy, pixelsizex, pixelsizey) -> raster - done see below* *ST_SelectByValue(raster, 'expression') -> same type as first argument* *ST_Clip(raster|geometry,geometry) -> same type as first argument*
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