The raster was just a quick way to make a vector index grid. If you can't get ST_AsRaster to work by upgrading to GDAL 1.9 use ST_MakeEmptyRaster and then ST_MapalgebraExpr with the '([rast.x] - 1) * ' || ST_Width(rast)::text || ' + [rast.y]' expression.
Then convert each pixel to a table of polygons with (ST_PixelAsPolygons(rast)).geom & (ST_PixelAsPolygons(rast)).val Then proceed with a normal geometry/geometry intersection. We don't have a very fast way to do that in raster mode right now. The fastest approach with what we have would probably be to use ST_MapAlgebraFct and write a custom function that generate the values by doing a point/geometry instersection with the road buffer table. Pierre > -----Original Message----- > From: postgis-users-boun...@postgis.refractions.net [mailto:postgis-users- > boun...@postgis.refractions.net] On Behalf Of Ed Linde > Sent: Thursday, March 22, 2012 5:03 PM > To: PostGIS Users Discussion > Subject: Re: [postgis-users] ST_Buffer + grid problem > > Oh and if you think there is a smarter way to do this, like maybe not making a > raster like I am trying to etc then please let me know. The idea is that the > road > geometry is way way smaller than the point cloud which is in Terabytes, so I > am > making a grid index in some way around the road buffers, to speed up the > computation. > > > On Thu, Mar 22, 2012 at 10:01 PM, Ed Linde <edoli...@gmail.com> wrote: > > > Hi Pierre, > The idea is that I want to build this uniform grid on the road geometry > and like you mention it has dimensions 1020x24798. I want to assign each cell > a > unique cell ID based on some formula like you had earlier ... x*width + y to > get a > 1D cell ID from (x,y). Hopefully I can do this on just (lat.long) of srid 4326 > directly. Then I need to > intersect it to the buffers around the roads which I think should be > easy > once I have a raster, so this is just a normal intersect. Now I should know > each > cell and what road buffer it belongs to! Then on my second data set which is a > massive point cloud with srid = 4326 as well, I just want to pass through it > ONCE > and compute in which cell it falls and hence associate a point with a road > buffer. > Hope that made sense :) > > Cheers, > Ed > > On Thu, Mar 22, 2012 at 9:53 PM, Pierre Racine > <pierre.rac...@sbf.ulaval.ca> wrote: > > > 1020x24798 so more than 25 000 000 polygons... or pixels... > > So if I understand well you want to assign some values to each > of those cells based on a vector coverage (of how many polygons)? > > > > -----Original Message----- > > From: postgis-users-boun...@postgis.refractions.net > [mailto:postgis-users- > > boun...@postgis.refractions.net] On Behalf Of Ed Linde > > > Sent: Thursday, March 22, 2012 4:43 PM > > To: PostGIS Users Discussion > > Subject: Re: [postgis-users] ST_Buffer + grid problem > > > > > So far no proper raster, because the following failed, but > maybe the polygon > > gives us an idea? This polygon is the extent of all the road > geometries in > > Denmark. Also I remember that when you did the raster at > your end you said it > > worked. Is 0.000036 degrees = 4m correct if I want to get a > 4m by 4m cell sized > > uniform raster grid? > > > > select ST_AsRaster( > ST_GeomFromText('POLYGON((8.07734039737749 > > 54.4984986588244,8.07734039737749 > 57.7505109647578,15.1919565742587 > > 57.7505109647578,15.1919565742587 > 54.4984986588244,8.07734039737749 > > 54.4984986588244))'), 0.000036, 0.000036); > > > > > > On Thu, Mar 22, 2012 at 9:39 PM, Pierre Racine > <pierre.rac...@sbf.ulaval.ca> > > wrote: > > > > > > > Thanks. The raster I need to visualise is a 4m by 4m > grid > on the entire > > map of > > > Denmark! :) So do you classify that as a large > raster? If so > is there a > > way to see a > > > portion of it or something? > > > I just want to manually check for a few areas on the > map > that the > > intersection > > > indeed works as expected and things haven't gone awry > thanks to > > projection > > > differences or that I had degrees instead of meters or > some such > > thing. Well, I > > > still have to first test if this GDAL upgrade will > fix things > and if make > > empty raster > > > .. makes a difference. > > > > > > That must be big but Danemark is a small country ;-) > Only > width and > > height tell you if a raster is big. > > > > In the database, your grid is a set of rectangular > geometry > (how many?) > > or just a big raster now (width & height)? > > > > _______________________________________________ > > 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 > > > _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
