NAME
s.surf.idw - Surface generation from sites data program.
(GRASS Raster Program)
SYNOPSIS
s.surf.idw input=name
output=name
[npoints=count]
DESCRIPTION
s.surf.idw fills a raster matrix with interpolated
values generated from a set of irregularly spaced data
points using numerical approximation (weighted averaging)
techniques. The interpolated value of a cell is determined
by values of nearby data points and the distance of the
cell from those input points. In comparison with other
methods, numerical approximation allows representation of
more complex surfaces (particularly those with anomalous
features), restricts the spatial influence of any errors,
and generates the interpolated surface from the data
points. It is the most appropriate method to apply to most
spatial data.
This program allows the user to use a GRASS site list file,
rather than a raster map layer, as input.
The program will be run non-interactively if the user
specifies the values of needed program parameters and any
desired optional parameter values on the command line,
using the form:
-
s.surf.idw input=name
output=name
[npoints=count]
Alternately, the user can simply type s.surf.idw on the command line,
without program arguments. In this case, the user will be prompted for
needed inputs and option choices using the standard GRASS
parser
interface.
OPTIONS
Parameters:
- input=name
- Name of an input site list file that contains a set of
irregularly spaced data values; i.e., some cells contain
known data values while the rest contain zero (0).
- output=name
- Name to be assigned to the new output raster map layer
containing a smooth surface generated from the known data
values in the input site list file.
- npoints=count
- The number of points to use for interpolation. By
default, the 12 nearest points are used for interpolation.
Default: 12
NOTES
The amount of memory used by this program is related to the
number of non-zero data values in the input sites
list file. If the input site list is very dense
(i.e., contains many non-zero data points), the program may
not be able to get all the memory it needs from the
system. The time required to execute increases with the
number of input data points.
If the user has a mask set, then interpolation is only done
for those cells that fall within the mask. However, all
non-zero data points in the input map are used even
if they fall outside the mask.
SEE ALSO
d.sites
g.region
r.mask
r.surf.contour
r.surf.idw
r.surf.idw2
r.surf.gauss
r.surf.fractal
r.surf.random
v.surf.rst
s.db.rim
s.menu
parser
AUTHOR
Michael Shapiro,
U.S. Army Construction Engineering
Research Laboratory