[postgis-users] Raster + Geometry Intersection

[Ed Linde]

Hi Pierre,
I used --> */root/postgis-svn/raster/loader/raster2pgsql -s 4326 -t 50x50
-I *.tif public.srtm_tiled > elev.sql*
for the loading. The switch in args did not make a difference
unfortunately! :(
I am pretty sure that the OSM roads geometry used SRID = 4326, and I think
the arguments I have
used to get in the tif files with the -s option also is right.
One warning I got while loading was (maybe it makes sense to you?) :

*/root/postgis-svn/raster/loader/raster2pgsql -s 4326 -t 50x50 -I *.tif
public.srtm_tiled > elev.sql
*Processing 1/4: srtm_38_01.tif
Processing 2/4: srtm_38_02.tif
*WARNING: Different geotransform matrices found in the set of rasters being
converted to PostGIS raster
*Processing 3/4: srtm_39_01.tif
Processing 4/4: srtm_39_02.tif

I tried loading the rasters and the roads in qgis, but it didn't manage to
show them together, so I am not sure why its
not aligning. I am sure its some sort of alignment issue, but do not see
where its wrong. I am getting the SRTM files
from http://gis-lab.info/data/srtm-tif/
And the OSM road was just the map for Denmark on OSM -->
http://download.geofabrik.de/osm/europe/

Is it possible for you to intersect these? I understand you are the author
of the postgis tutorial that I am trying to follow
to achieve the same...hence I ask. :)

Cheers,
Ed


On Mon, Feb 27, 2012 at 2:58 PM, Pierre Racine
<Pierre.Racine at sbf.ulaval.ca>wrote:

>
>
> > -----Original Message-----
> > From: postgis-users-bounces at postgis.refractions.net [mailto:
> postgis-users-
> > bounces at postgis.refractions.net] On Behalf Of Ed Linde
> > Sent: Monday, February 27, 2012 7:21 AM
> > To: postgis-users at postgis.refractions.net
> > Subject: [postgis-users] Raster + Geometry Intersection
> >
> > Hi,
> > I am trying to compute elevations for a road network that I have
> downloaded
> > and installed into my pg database using osm2pgsql. I also have loaded
> SRTM tif
> > files and they are stored as type RASTER in my table.
> > I am now trying to compute an intersection between the SRTM rasters and
> the
> > OSM road geometries... with no luck! :( I am following this tutorial -->
> > http://trac.osgeo.org/postgis/wiki/WKTRasterTutorial01
> > but I think it might be slightly outdated.
>
> The base queries to do the intersection are still valid. Only the
> uploading changed. And not much.
>
> >  SELECT o.osm_id,
> >         ST_Intersection(s.rast, o.way)
> >  FROM planet_osm_line o,
> >       srtm_tiled s
> >  WHERE ST_Intersects(s.rast, o.way);
> >
> > way type -->   way geometry(LineString,900913)
> >
> > CREATE TABLE public.srtm_tiled
> > (
> >   rid integer NOT NULL DEFAULT nextval('srtm_tiled_rid_seq'::regclass),
> >   rast raster,
> >   CONSTRAINT srtm_tiled_pkey PRIMARY KEY (rid)
> > )
> > WITH (
> >   OIDS=FALSE
> > );
> >
> > performing the above query returns no rows. So I am not sure what is
> wrong.. or
> > if I am doing this query correctly. Is the SRID set differently in the
> raster and
> > geometry?
>
> You should do ST_Intersection(o.way , s.rast) instead of
> ST_Intersection(s.rast, o.way). The first operates in the vector world and
> the second in the raster world. Let me know if that makes a difference in
> terms of results.
>
> Are the SRIDs identical? Did you make sure that the raster were loaded
> properly by displaying values with ST_Value() or ST_DumpAsPolygons() or
> simply displaying the raster in QGIS? Does the raster align with the roads
> properly?
>
> > I also loaded the tif files using the tutorial, but I used the C version
> not the
> > python loader because I understand its been deprecated.
>
> Should not make any difference.
>
> Pierre
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