Markus Metz wrote: > > I am trying to work around with a problem of map size under Vista (>2G). > > I was wondering if I use the command below I will get a raster > > map with values integer and >=0. > > r.mapcalc "Dem.new=if(Dem>=0,int(Dem),null())" > > If the original DEM is of type DCELL, you can reduce file sizes with > r.mapcalc "DEM.float = float(DEM)" > because one DCELL value needs 8 byte whereas both FCELL and CELL values > need 4 bytes each. > Converting from FCELL to CELL doesn't make a big difference, I even > found that sometimes FCELL raster maps are higher compressed in GRASS > than CELL raster maps.
FP data is compressed using zlib. Integer data normally uses RLE compression, although it can be made to use zlib by setting the environment variable GRASS_INT_ZLIB (the value doesn't matter). Also, integer data may use between 1 and 4 bytes per cell. Each row has a prefix byte which indicates how many bytes per cell are used for that row. Negative values always require 4 bytes. -- Glynn Clements <gl...@gclements.plus.com> _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user