On 09/29/2012 10:40 PM, Lars Dalby wrote:
Hi Micha Thanks a lot for your detailed response! Much appreciated.Micha Silver wroteIf I understand your task, you want to * import the GLWD lakes polygon shapefile into GRASS * reproject to a projected CRS * create a GRID with cell size about 92 km. X 92 km, and * sum up the area of lakes within each grid cell.Correct, that's exactly what I am trying to do! Micha Silver wroteFirst I downloaded the polygon shapefile you linked to. THen I started GRASS in a WGS84 based LOCATION, and used: # Use the '-o' option since the downloaded shapefile does not have a *.prj v.in.ogr -o dsn=glwd_2.shp out=glwdYep, that also what I did. Micha Silver wroteNext I restarted GRASS and created a new location based on the EPSG code 3925. This is NOT World Behrmann, but it's a cylindrical equal area projection with meters as units, like Behrmann. I couldn't find any proj4 reference to Behrmann :-(I know, it is actually a bit surprising because it is quite commonly used, at least in large-scale ecology which is my field of study. I have defined the location myself so not a big problem. Anyhow, the steps needed in this example does not really depend on a specific projection, so it should work just fine no matter what projection is being used. Micha Silver wroteAt this step, I made sure to set the default database connection to sqlite. (This is important later to aggregate the water body areas in each grid cell.): eval `g.gisenv` db.connect driver=sqlite database=$GISDBASE/$LOCATION_NAME/$MAPSET/sqlite.dbI was able to excecute the db.connect command and I guess that I don't have to use eval `g.gisenv` when I am running the commands via R? Micha Silver wroteNow: v.proj in=glwd loc= <the WGS84 LOCATION> map= <the previous MAPSET>I did this step earlier also, but redid it here because the database connection was changed. Micha Silver wroteNext step, I created a grid using v.mkgrid. I limited the region to just Africa so things would move along a little faster. So something like: # Create a vector grid with size 92,000 meters by 92,000 meters v.mkgrid --o grid92 position=coor coor=-2000000,-5000000 box=92000,92000 grid=140,85 # I got the 'grid=' parameters by dividing the length and width by 92,000 So, this is as far as I could get in this round. When I'm running this command I get an error message: "Parameter <coor> does not have float value". I figure that this means that my coor values are not floating points. They look like this: coor = -6358820,-17367529. Shouldn't that be ok? Can you copy/paste your exact command? I think there should not be any space between 'coor' and '='. Hmm..., not sure what to do here. Any hints? Best Lars -- View this message in context: http://osgeo-org.1560.n6.nabble.com/Rasterize-polygons-multiple-polygons-per-grid-cell-tp5005264p5005355.html Sent from the Grass - Users mailing list archive at Nabble.com. _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user This mail was received via Mail-SeCure System. -- Micha Silver GIS Consultant, Arava Development Co. http://www.surfaces.co.il |
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