[GRASS-user] WCS import into GRASS GIS - select region extent only

[Markus Neteler]

Hi,

just for fun I have made a test with r.external (of GRASS GIS 7, it
potentially works with G6 as well):

# create ASCII file with this content, named e.g. "wcs_geoserver_LL.wcs":
<WCS_GDAL>
  <ServiceURL>http://demo.opengeo.org/geoserver/wcs?</ServiceURL>
  <CoverageName>Img_Sample</CoverageName>
</WCS_GDAL>

or download this file from
http://svn.osgeo.org/gdal/trunk/autotest/gdrivers/data/geoserver.wcs

Start GRASS in latlong location, then

GRASS 7.0.svn (latlong):~ > r.external input=wcs_geoserver_LL.wcs
output=wcs_data --o
Projection of input dataset and current location appear to match
Reading band 1 of 3...
r.external complete. Link to raster map <wcs_data.1> created.
Reading band 2 of 3...
r.external complete. Link to raster map <wcs_data.2> created.
Reading band 3 of 3...
r.external complete. Link to raster map <wcs_data.3> created.
Imagery group <wcs_data> created

Interestingly the content of wcs_geoserver_LL.wcs is expanded on the
fly, i.e. the file is rewritten.
BTW I had to run r.external twice on the same file to avoid some GDAL
errors (perhaps the demo server is simply stressed).

GRASS 7.0.svn (latlong):~ > g.region rast=wcs_data.1 -p
projection: 3 (Latitude-Longitude)
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      54:06:50.76N
south:      20:42:18.72N
west:       130:51:06.048W
east:       62:00:19.44W
nsres:      0:03:21.123813
ewres:      0:04:12.132867
rows:       598
cols:       983
cells:      587834

Voilà, the WCS layer is loaded (then I used the RGB viewer in the wxGUI).

Eventually I then played around with the bounding box
(BBOX=minx,miny,maxx,maxy) and "injected" it in above small file
<GetCoverageExtra>&bbox=-103.93,33.74-93.4940.61</GetCoverageExtra>

so that it becomes:

<WCS_GDAL>
  <ServiceURL>http://demo.opengeo.org/geoserver/wcs?</ServiceURL>
  <CoverageName>Img_Sample</CoverageName>
  <GetCoverageExtra>&bbox=-103.93,33.74-93.4940.61</GetCoverageExtra>
</WCS_GDAL>

BUT, as stated in
http://lists.osgeo.org/pipermail/gdal-dev/2008-March/016552.html
it does not have any effect.
I don't know if it would make sense to implement a "projwin" parameter
in r.external.

BTW: Another file/WCS server to play with is
http://svn.osgeo.org/gdal/trunk/autotest/gdrivers/data/srtmplus.wcs

Not really helpful but at least we know that r.external works with WCS servers.

Markus