This program may be especially useful when sampling for cross validation of interpolations whose output is a raster map.
When NULL values are encountered for a cell, zero value is used instead. In these cases, more acurrate results may be obtained by using the default nearest neighbor comparisons.
This program may not work properly with lat-long data when the -bc flags are used.
When interpolation is done (i.e., the -bc flags are used), values are assumed to be located at the centroid of grid cells. Therefore, current resolution settings are important.
# set computational region: g.region raster=elev_srtm_30m -p # generate random points: v.random output=random n=100 # add table with one column: v.db.addtable random col="elev_srtm30 double precision" # transfer elevations at random points into table: v.what.rast map=random rast=elev_srtm_30m col=elev_srtm30 # verify: v.db.select random # perform sampling on other elevation map: v.sample in=random col=elev_srtm30 rast=elev_ned_30m out=elev_samples #verify: v.db.select elev_samples #univariate statistics of differences between elevation maps: v.univar elev_samples column=diff type=point
Updated for GRASS 5.0 by Eric G. Miller
Updated for GRASS 5.7 by Radim Blazek
Last changed: $Date$