GSP
Quick Navigator

Search Site

Unix VPS
A - Starter
B - Basic
C - Preferred
D - Commercial
MPS - Dedicated
Previous VPSs
* Sign Up! *

Support
Contact Us
Online Help
Handbooks
Domain Status
Man Pages

FAQ
Virtual Servers
Pricing
Billing
Technical

Network
Facilities
Connectivity
Topology Map

Miscellaneous
Server Agreement
Year 2038
Credits
 

USA Flag

 

 

Man Pages
v.sample(1) Grass User's Manual v.sample(1)

v.sample - Samples a raster map at vector point locations.

vector, sampling, raster

v.sample
 
v.sample --help
 
v.sample input=name [layer=string] column= name output=name raster=name [ method=string] [zscale=float] [--overwrite] [-- help] [--verbose] [--quiet] [--ui]

--overwrite
 
Allow output files to overwrite existing files
--help
 
Print usage summary
--verbose
 
Verbose module output
--quiet
 
Quiet module output
--ui
 
Force launching GUI dialog

input=name [required]
 
Name of input vector point map
 
Or data source for direct OGR access
layer=string
 
Layer number or name
 
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
 
Default: 1
column=name [required]
 
Name of attribute column to use for comparison
output=name [required]
 
Name for output vector map to store differences
raster=name [required]
 
Name of raster map to be sampled
method=string
 
Sampling interpolation method
 
Options: nearest, bilinear, bicubic
 
Default: nearest
 
nearest: Nearest-neighbor interpolation
 
bilinear: Bilinear interpolation
 
bicubic: Bicubic interpolation
zscale=float
 
Scaling factor for values read from raster map
 
Sampled values will be multiplied by this factor
 
Default: 1.0

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.

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.

Comparison of "elev_ned_30m" and "elev_srtm_30m" North Carolina sample dataset elevation models at random positions:
 
# 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

g.region, v.random, v.what.rast Image Sampling Methods - GRASS Tutorial on s.sample (available as s.sample-tutorial.ps.gz)

James Darrell McCauley
 
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: 2014-12-19 22:17:36 +0100 (Fri, 19 Dec 2014) $

Available at: v.sample source code (history)
Main index | Vector index | Topics index | Keywords index | Graphical index | Full index
© 2003-2018 GRASS Development Team, GRASS GIS 7.4.3 Reference Manual
GRASS 7.4.3

Search for    or go to Top of page |  Section 1 |  Main Index

Powered by GSP Visit the GSP FreeBSD Man Page Interface.
Output converted with ManDoc.