NAME
v.sample - Sample a raster file at site locations.
SYNOPSIS
v.sample
v.sample help
v.sample [-BCq] input=string column=string output=string rast=string [z=float]
Flags:
- -B
- Bilinear interpolation [default is nearest neighbor]
- -C
- Cubic convolution interpolation [default is nearest neighbor]
- -q
- Quiet
Parameters:
- input=string
- vector defining sample points
- column=string
- Attribute column
- output=string
- vector to store differences
- rast=string
- raster file to be sampled
- z=float
- Option scaling factor for values read from raster map. Sampled values will be multiplied by this factor.
- Default: 1.0
DESCRIPTION
v.sample samples a GRASS raster map at the point
locations in the input file by either cubic convolution
interpolation, bilinear interpolation, or nearest neighbor
sampling (default).
This program may be especially useful when sampling for
cross validation of interpolations whose output is a raster
map.
NOTES
The output points will have the easting and northing of the input points.
The input category value is used. The input attribute, raster value
and difference is written to output.
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.
SEE ALSO
s.random
g.region
Image Sampling Methods - GRASS Tutorial on s.sample
(available as
s.sample-tutorial.ps.gz)
BUGS
Please send all bug fixes and comments to the author
or the grass development team.
http://grass.itc.it
AUTHOR
James Darrell McCauley
<darrell@mccauley-usa.com>,
when he was at:
Agricultural
Engineering
Purdue University
Updated for GRASS 5.0 by Eric G. Miller
Updated for GRASS 5.7 by Radim Blazek
Last changed: $Date: 2005/02/03 10:59:51 $