I'm still trying to understand PostGIS Raster especially regarding analysis and viewing PostGIS raster data. Let's begin with the latter.
Viewing: => What are the pros & cons to do this (and which is preferred?): ST_DumpAsPolygons or ST_PixelAsPolygons? Here is an example for viewing PostGIS Raster e.g. in OpenJUMP I found in the Tutorial (http://trac.osgeo.org/postgis/wiki/WKTRasterTutorial01 ) SELECT ST_AsBinary((ST_DumpAsPolygons(rast)).geom), (ST_DumpAsPolygons(rast)).val FROM srtm_tiled WHERE rid=3278; This seems to polygonize raster to vector. Unfortunately it's not explained in the tutorial what the constraint clause "rid=3278" means: it's obviously a single, distinct tile(?). From the book "PostGIS in Action": "ST_DumpAsPolygons returns a set of single polygon, pixvalue pairs for a given raster band and relies on the GDAL library. In many cases this function will be easier and faster to use than going down to the level of the pixel using ST_Value.". A solution for doing this I found here as a pl/pgsql function called ST_PixelAsPolygons (http://trac.osgeo.org/postgis/wiki/WKTRasterUsefulFunctions). Analysis: Regarding analysis I'd like to begin with the observation, that all examples I've found so far are polygonizing rasters to vector. From the tutorial doing overlay: CREATE TABLE caribou_srtm_inter AS SELECT id, (ST_Intersection(rast, the_geom)).geom AS the_geom, (ST_Intersection(rast, the_geom)).val FROM cariboupoint_buffers_wgs, srtm_tiled WHERE ST_Intersects(rast, the_geom); => What is the intended exact result type of this overlay operation query (ST_Intersects)? POINT? => Which query would generate another raster layer (instead of a point vector like in the above example)? Yours, S. _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
