[postgis-users] ST_Buffer + grid problem

[Ed Linde]

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 <edolinde at 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.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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