NAME
r.surf.idw2 - Surface generation program.
(GRASS Raster Program)
SYNOPSIS
r.surf.idw2
input=name output=name
[npoints=count]
DESCRIPTION
r.surf.idw2 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.
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:
-
r.surf.idw2 input=name
output=name [npoints=count]
Alternately, the user can simply type r.surf.idw2 on the command line,
without program arguments. In this case, the user will be prompted for
parameter values using the standard GRASS user interface
described in the manual entry for
parser.
Parameters:
- input=name
- Name of an input raster map layer 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 map layer.
- npoints=count
- The number of points to use for interpolation. The
default is to use the 12 nearest points when interpolating
the value for a particular cell.
Default: 12
NOTES
The amount of memory used by this program is related to the
number of non-zero data values in the input map layer. If
the input raster map layer 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 layer are used even if
they fall outside the mask.
This program does not work with latitude/longitude data
bases. Another surface generation program, named
r.surf.idw,
should be used with latitude/longitude data bases.
The user should refer to the manual entries for
r.surf.idw
r.surf.contour
s.surf.idw
s.surf.rst
to
compare this surface generation program with others available in GRASS.
SEE ALSO
r.mask
r.surf.contour
r.surf.idw
s.surf.idw
s.surf.rst
r.surf.gauss
r.surf.fractal
r.surf.random
r.surf.idw2
v.surf.rst
parser
AUTHOR
Michael Shapiro, U.S.Army Construction Engineering
Research Laboratory