You want one value per polygon or one value per red point? It is not clear to me from your drawing.
Pierre > -----Original Message----- > From: postgis-users-boun...@postgis.refractions.net [mailto:postgis-users- > boun...@postgis.refractions.net] On Behalf Of Francois Hugues > Sent: Saturday, May 26, 2012 5:29 PM > To: postgis-users@postgis.refractions.net > Subject: [postgis-users] get unique values from raster intersecting a polygon > > Hello list, > > I have to get values from raster where they intersect polygons from a layer > with > numerous polygons which have shared boundaries, but I don't want to have > duplicate values from raster. The final result must be something like : gid | > val. > > To explain my case, I made a picture. > > I think ST_intersection could help but I don't know what will be the exact > result. > In my example, we have a grid (a DEM for example), each red point is the value > in the centre of each cell and two polygons A and B. I think cells totally > within > polygons are not a problem, but in green I have highlighted some ambiguous > cases : > - 1 and 2 are cells shared by both polygons but not in the same proportions > and I > would like to get value 1 for polygon A but not for B and value 2 for polygon > B > but not for A > - What will be the result for cell number 3 and for the other green cell > without > number (and for all the ones which are not totally within a polygon) ? I > think the > value is the same for the whole cell (st_dumpaspolygon) and will be returned > whatever the part of the cell covered by the polygon, but if someone could > confirm. > > If st_intersection use st_DumpAsPolygon, could it be better to work directly > with > this polygonized table using its own gist index and dealing with shared areas > of > cells between different polygons ? > > Hugues. > > > > _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
