[postgis-users] ST_Buffer + grid problem

[Ed Linde]

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.Racine at 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-bounces at postgis.refractions.net [mailto:
> postgis-users-
> > bounces at 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.Racine at 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)?
> >
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>
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