Hi, I'm new to PostGIS, at least in the backend, so please excuse my naive question, but I couldn't figure this out Googling.
So, I've got it all working (PostGIS 2.0, imported the raster file and got the right projection information etc). SELECT PostGIS_full_version(); postgis_full_version ----------------------------------------------------------------------------------------------------------------------------------------------------- POSTGIS="2.0.1 r9979" GEOS="3.3.5-CAPI-1.7.5" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.9.1, released 2012/05/15" LIBXML="2.7.8" TOPOLOGY RASTER (1 row) Now I come to querying but cannot seem to get there. I would like to make a simple point query for the height in a point on the raster that we have. I tried this: select st_value(rast,ST_Point(1821416, 5649720)) from nzdem3; where ST_Point(1821416, 5649720) is in NZTM (EPSG:2193). However, it doesn't work and just complains it is out of range. So, I did some research and found that it wants the pixel coordinate. Now, I could calculate it by getting the Geo Transformation with GDAL etc, but what is the point of PostGIS if I have to use GDAL instead? The point is that I would like to use PostGIS, because it seems like it's much more powerful. And we have PostGIS running anyway and it seems like the sensible choice. I also tried this: select DISTINCT ST_World2RasterCoordX(rast,ST_Point(1821416, 5649720)) from nzdem3; but that gives me a pixel offset for each row in the database which really confuses me. How am I supposed to query if there are 56 different values for x alone: st_world2rastercoordx ----------------------- -6038 10762 40762 -4838 31162 33562 38362 -38 45562 14362 19162 7162 11962 21562 -13238 20362 46762 1162 8362 -14438 27562 15562 26362 -15638 28762 -9638 -2438 -12038 49162 3562 37162 39562 22762 9562 35962 -3638 -16838 4762 47962 5962 34762 2362 41962 25162 17962 23962 -1238 16762 -7238 32362 13162 43162 -8438 -10838 44362 29962 (56 rows) I see that PostGIS has a lot of potential also with raster queries and ultimately, I would like to be able to intersect it with a line string or even a multi poligon. But for now I would be happy if I could get a point with the projection's geographic coordinates. Please help! Thanks, Tim Tim-Hinnerk Heuer Twitter: @geekdenz Blog: http://www.thheuer.com
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