[postgis-users] ST_Buffer + grid problem

[Ed Linde]

Hi Pierre,
So I am trying to have a 4meter by 4meter cell and I converted 4meters to
degrees, because I think
ST_Extent will compute it in degrees as my geometry is in srid 4326. But I
get this GDAL error which
I have no clue what it means. Any ideas how I can fix it? Also I noticed
that if I set it to 1.0, 1.0 I get
21 rows but the gridid isn't continuous either (which is weird).

CREATE TABLE vectorgrid AS
SELECT (gvxy).geom, ((gvxy).x - 1) * rwidth + (gvxy).y gridid
FROM (SELECT ST_PixelAsPolygons(rast) gvxy, ST_Width(rast) rwidth
            FROM (SELECT ST_AsRaster(ST_Extent(way_geom)::geometry,
0.000036, 0.000036) rast
                         FROM buffers
                        ) foo1
           ) foo2;

ERROR:  rt_raster_gdal_rasterize: Unable to add band to GDALDataset

********** Error **********

ERROR: rt_raster_gdal_rasterize: Unable to add band to GDALDataset
SQL state: XX000



On Thu, Mar 22, 2012 at 2:13 PM, Pierre Racine
<Pierre.Racine at sbf.ulaval.ca>wrote:

> You can control how the grid is aligned by using more ST_AsRaster
> parameters. See:
>
> http://postgis.refractions.net/documentation/manual-svn/RT_ST_AsRaster.html
>
> If you want it to align on your point, just align it on your points...
>
> Pierre
>
> > -----Original Message-----
> > From: manohar.kaul at gmail.com [mailto:manohar.kaul at gmail.com] On Behalf
> > Of Ed Linde
> > Sent: Thursday, March 22, 2012 9:05 AM
> > To: PostGIS Users Discussion
> > Cc: Pierre Racine
> > Subject: Re: [postgis-users] ST_Buffer + grid problem
> >
> > Hi Pierre,
> > Thanks for the grid idea last night. I have a problem though, I want to
> have a 4m
> > by 4m cell sized grid over my buffer geometries which are in SRID =
> 4326. And
> > then I have another data set of 2D points which are also in SRID 4326...
> > wondering how I can figure out from just a given (lat,long) which cell
> ID in the
> > buffer grid it would belong to? I am thinking that I might run into
> "alignment
> > issues" because shouldn't the extent of the grid be exactly the same on
> the 2D
> > point cloud as well, so that the grid cell IDs will match? Unless I am
> missing
> > something here?
> >
> > Cheers,
> > Ed
> >
> >
> >
> > On Wed, Mar 21, 2012 at 8:46 PM, Pierre Racine <
> Pierre.Racine at sbf.ulaval.ca>
> > wrote:
> >
> >
> >       > I am not sure if this is possible, but I have computed (using
> ST_Buffer)
> > a sort of
> >       > buffer around several LINESTRINGs. Now I would like to lay some
> sort
> > of grid of
> >       > say 1m^2 cell size on top of this collection of geometries and
> then
> > compute the
> >       > intersection... so in the end I would like to for example, know
> that grid
> > cell ID = 1
> >       > intersects with buffers 1 and 10, grid cell 2 intersects with
> buffers 7, 10
> > etc..
> >       >
> >       > Is there a simple way of doing this in postgis? Maybe someone
> could
> > point me to
> >       > some documentation of how I can generate such a grid in postgis
> and
> > maybe
> >       > then I can use just ST_Intersect once I have these two
> geometries?
> >
> >
> >       With the raster type you can now easily create a vector grid like
> this:
> >
> >       CREATE TABLE vectorgrid AS
> >       SELECT (gvxy).geom, ((gvxy).x - 1) * rwidth + (gvxy).y gridid
> >       FROM (SELECT ST_PixelAsPolygons(rast) gvxy, ST_Width(rast) rwidth
> >                   FROM (SELECT ST_AsRaster(ST_Extent(geom)::geometry,
> 1.0,
> > 1.0) rast
> >                                FROM yourbuffertable
> >                               ) foo1
> >                  ) foo2;
> >
> >       Make sure a spatial index exist on both tables:
> >
> >       CREATE INDEX yourbuffertable_geom_idx  ON yourbuffertable USING
> > gist  (geom);
> >       CREATE INDEX vectorgrid _geom_idx  ON vectorgrid USING gist
> > (geom);
> >
> >       You can then perform a normal intersect query:
> >
> >       CREATE TABLE interresult AS
> >       SELECT b.bufferid, g.gridid, ST_Intersection(g.geom, b.geom) geom
> >       FROM vectorgrid g, yourbuffertable b
> >       WHERE ST_Intersects(g.geom, b.geom);
> >
> >       Pierre
> >       _______________________________________________
> >       postgis-users mailing list
> >       postgis-users at postgis.refractions.net
> >       http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
>
>
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