Hi Micha Thanks a lot for your detailed response! Much appreciated.
Micha Silver wrote > If 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 wrote > First 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=glwd Yep, that also what I did. Micha Silver wrote > Next 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 wrote > At 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.db I 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 wrote > Now: > 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 wrote > Next 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? 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 [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
