NAME

       r.surf.idw2  - Surface generation program.

KEYWORDS

       raster, interpolation

SYNOPSIS

       r.surf.idw2
       r.surf.idw2 help
       r.surf.idw2   input=name   output=name    [npoints=count]     [--overwrite]    [--verbose]
       [--quiet]

   Flags:
       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name
           Name of input raster map

       output=name
           Name for output raster map

       npoints=count
           Number of interpolation points
           Default: 12

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 npoints parameter defines 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.

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
       v.surf.rst
       to compare this surface generation program with others available in GRASS.

SEE ALSO

       r.surf.contour,  r.surf.idw,  r.surf.gauss,  r.surf.fractal,  r.surf.random,  r.surf.idw2,
       v.surf.rst

AUTHOR

       Michael Shapiro, U.S.Army Construction Engineering Research Laboratory

       Last changed: $Date: 2008-05-16 12:09:06 -0700 (Fri, 16 May 2008) $

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       © 2003-2013 GRASS Development Team