Hugues, You should be able to use ST_MapAlgebraNgb if you have PostGIS 2.0. But there may be challenges working with neighboring tiles.
PostGIS 2.1 has more robust handling with ST_MapAlgebra. http://www.postgis.net/docs/manual-2.1/RT_ST_MapAlgebra.html See the example with the description "Complete example of tiles of a coverage with neighborhood. This query only works with PostgreSQL 9.1 or higher.". -bborie On 07/02/2013 09:47 AM, Hugues François wrote: > Hello, > > Given a one band raster made of numerous tiles and a point geometry from > which I select one pixel, I would like to compare its value with its (8) > neighbors' values. For now I do that with st_value(rast, geom) and playing > with point coordinates (x +/- pixel width and y +/- height) : it works fine > but it is very slow and I have to make a loop to compare selected pixels' > values with their neighbors until I reach a certain value. > > What I would like is to do all that only with raster but I don't see how to > compare one pixel value with its neighbors (within the same tile or into a > neighbor tile). I assume I miss something and this is obvious for some of > you, so if you could give a hand, i would be sincerely grateful. > > Regards, > > Hugues. > _______________________________________________ > postgis-users mailing list > [email protected] > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users > _______________________________________________ postgis-users mailing list [email protected] http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
