Hi, I'm a newbie in PostGIS Raster use and GIS applications, so this may be a dumb question. I'm a little confused by some functionalities and I don't know if it's possible to do what i'm trying to. Basically, I'm using postgis functions either for raster and vector forms of an image and I'm trying to visualize parts of the raster by using the informations presented only in the shapefile. For example, I have an TIFF file of a land coverage (one band) about 49746 x 71819 and it's shapefile with some grid codes. I'm doing the following query to extract pixel values from an expecific gridcode (18) presented in the shapefile imported (vector_table) so I could infer some grid codes by the pixel value:
SELECT (gval).val as pixel_value FROM ( SELECT ST_DumpAsPolygons(ST_Clip(rast,1,geom)) as gval from raster_table join vector_table on (st_intersects(rast,geom)) where geom in (select geom from vector_table where gridcode = 18) ) as intersection; The query runs too slow and I don't know how to optimize it. The raster image is big and I tried different tiles configurations (100x100, 200x200, 1000x1000) and 100x100 seemed to have better perfomance. I'm using st_clip for a faster answer. I don't know if these pixels values would retrieve some important information and if PostGIS raster is really suitable with area calculations. Is there a way to optimize the query or postgis raster isn't suitable for this case? -- View this message in context: http://postgis.17.x6.nabble.com/PostGIS-Raster-Performance-tp5006902.html Sent from the PostGIS - User mailing list archive at Nabble.com. _______________________________________________ postgis-users mailing list [email protected] http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
