In PostGIS you can easily create a grid with ST_MakeEmptyRaster() and ST_PixelAsPolygons()
Pierre > -----Original Message----- > From: postgis-users-boun...@postgis.refractions.net [mailto:postgis-users- > boun...@postgis.refractions.net] On Behalf Of pcr...@pcreso.com > Sent: Monday, May 28, 2012 3:45 PM > To: PostGIS Users Discussion > Subject: Re: [postgis-users] RE : get unique values from raster intersecting > apolygon > > You could try something like gdal2xyz.py on you raster to create points for > each > raster cell which can be imported directly into postgis as point geometries, > like: > > psql "create table xyz (id serial,x decimal, y decimal, z decimal)" > gdal2xyz.py <raster file> | psql "copy xyz (x,y,z) from stdin..." > psql "select addgeometrycolumn()" > psql "update xyz set geom=setsrid(makepoint(x,y),<srid>)" > > The result is then a simple spatial join using the polygons & the new points, > based on ST_Contains(). > > > HTH, > > Brent Wood > > > --- On Tue, 5/29/12, Francois Hugues <hugues.franc...@irstea.fr> wrote: > > > > From: Francois Hugues <hugues.franc...@irstea.fr> > Subject: [postgis-users] RE : get unique values from raster intersecting > apolygon > To: "PostGIS Users Discussion" <postgis-users@postgis.refractions.net> > Date: Tuesday, May 29, 2012, 1:05 AM > > > I want one value per red point (which are raster data). > > The gid of one polygon will appear as many times as necessary > regarding how it intersects the raster. > > Hugues. > > > -------- Message d'origine-------- > De: postgis-users-boun...@postgis.refractions.net de la part de Pierre > Racine > Date: lun. 28/05/2012 14:24 > À: PostGIS Users Discussion > Objet : Re: [postgis-users] get unique values from raster intersecting > apolygon > > 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 > > > > -----Inline Attachment Follows----- > > > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users > _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
