1v.surf.idw(1)                 Grass User's Manual                v.surf.idw(1)
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NAME

6       v.surf.idw   -  Surface interpolation from vector point data by Inverse
7       Distance Squared Weighting.
8

KEYWORDS

10       vector
11

SYNOPSIS

13       v.surf.idw
14       v.surf.idw help
15       v.surf.idw    [-n]    input=name     output=string      [npoints=count]
16       [layer=integer]   [column=string]
17
18   Flags:
19       -n  Don't  index points by raster cell (slower but uses less memory and
20           includes points from outside region in the interpolation)
21
22   Parameters:
23       input=name
24           Name of input vector map
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26       output=string
27           Name of output raster map
28
29       npoints=count
30           Number of interpolation points Default: 12
31
32       layer=integer
33           Field value. If set to 0, z coordinates are used. (3D vector  only)
34           Default: 1
35
36       column=string
37           Attribute table column with values to interpolate (if layer>0)
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DESCRIPTION

40       v.surf.idw  fills  a  raster  matrix with interpolated values generated
41       from a set of irregularly spaced data points using numerical approxima‐
42       tion  (weighted averaging) techniques. The interpolated value of a cell
43       is determined by values of nearby data points and the distance  of  the
44       cell from those input points.  In comparison with other methods, numer‐
45       ical approximation allows representation of more complex surfaces (par‐
46       ticularly  those with anomalous features), restricts the spatial influ‐
47       ence of any errors, and generates the  interpolated  surface  from  the
48       data points.
49
50       This  program  allows  the  user  to use a GRASS vector point map file,
51       rather than a raster map layer, as input.
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NOTES

54       The amount of memory used by this program is related to the  number  of
55       sites  in  the  current  region.  If the vector point map is very dense
56       (i.e., contains many data points), the program may not be able  to  get
57       all  the memory it needs from the system.  The time required to execute
58       is related to the resolution of the current region,  after  an  initial
59       delay determined by the time taken to read the input sites file.
60
61       If  the  user has a mask set, then interpolation is only done for those
62       cells that fall within the mask. However,  all  sites  in  the  current
63       region  are  used even if they fall outside the mask. Sites outside the
64       current region are not used in the interpolation. A larger  region  may
65       be  set  and a mask used to limit interpolation to a smaller area if it
66       is desired to use sites from outside the region in  the  interpolation.
67       The -n flag may also be used to achieve a similar result.
68
69       If  more than count sites fall into one target raster cell, the mean of
70       all the site values will determine the cell value (unless the  -n  flag
71       is  specifed,  in which case only the count sites closest to the centre
72       of the cell will be interpolated).
73
74       By setting npoints=1, the  module  can  be  used  to  calculate  raster
75       Voronoi diagrams (Thiessen polygons).
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SEE ALSO

78       d.vect
79       g.region
80       r.surf.contour
81       r.surf.idw
82       r.surf.idw2
83       r.surf.gauss
84       r.surf.fractal
85       r.surf.random
86       v.surf.rst
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AUTHOR

89       Michael Shapiro, U.S. Army Construction Engineering Research Laboratory
90       Improved algorithm (indexes points according to cell and ignores points
91       outside current region) by Paul Kelly
92
93       Last changed: $Date: 2006/04/20 21:31:24 $
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95       Full index
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99GRASS 6.2.2                                                      v.surf.idw(1)