Thanks I will try and see how I go with all your suggestions tomorrow... hopefully you will be around to help. :) I have to play around more with ST_MapalgebraExpr to understand how what you say works... like what is a "single band" and "double band" raster? Does that just mean that in a single band the raster cells will have a 1D value as opposed to a 2D (x,y) in the double band? Once the intersection between the road buffer geometry and this new raster is done, then the point cloud stuff I will have to write some code in C/C++ to handle that, so that shouldn't be a problem. One last thing, is it ok to treat srid 4326's lat/long points as normal x,y co-ordinates? I ask because when I try to compute if a point falls within the raster extent or not ... then I can just treat it as trying to figure out if a point lie within a rectangle or not, where I know the lower left and top right corner's (lat,long) co-ordinates. Is that still ok? Or am I overlooking something?
On Thu, Mar 22, 2012 at 10:17 PM, Pierre Racine <pierre.rac...@sbf.ulaval.ca > wrote: > 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 >
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