[postgis-users] ST_Buffer + grid problem

[Ed Linde]

Thanks Pierre for the detailed information. I will give this a shot
tomorrow and see how it goes! :)

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
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-users/attachments/20120321/2596f155/attachment.html>