1v.surf.idw(1) Grass User's Manual v.surf.idw(1)
2
6 v.surf.idw - Surface interpolation from vector point data by Inverse
7 Distance Squared Weighting.
8
10 vector, interpolation
11
13 v.surf.idw
14 v.surf.idw help
15 v.surf.idw [-n] input=name output=name [npoints=count] [layer=inte‐
16 ger] [column=string] [--overwrite] [--verbose] [--quiet]
17 Flags:
19 -n
20 Don't index points by raster cell
21 Slower but uses less memory and includes points from outside region
22 in the interpolation
23 --overwrite
25 Allow output files to overwrite existing files
26 --verbose
28 Verbose module output
29 --quiet
31 Quiet module output
32 Parameters:
34 input=name
35 Name of input vector map
36 output=name
38 Name for output raster map
39 npoints=count
41 Number of interpolation points
42 Default: 12
43 layer=integer
45 Layer number
46 If set to 0, z coordinates are used (3D vector only)
47 Default: 1
48 column=string
50 Attribute table column with values to interpolate
51 Required if layer > 0
52
54 v.surf.idw fills a raster matrix with interpolated values generated
55 from a set of irregularly spaced data points using numerical approxima‐
56 tion (weighted averaging) techniques. The interpolated value of a cell
57 is determined by values of nearby data points and the distance of the
58 cell from those input points. In comparison with other methods, numer‐
59 ical approximation allows representation of more complex surfaces (par‐
60 ticularly those with anomalous features), restricts the spatial influ‐
61 ence of any errors, and generates the interpolated surface from the
62 data points.
63 This program allows the user to use a GRASS vector point map file,
65 rather than a raster map layer, as input.
66
68 The amount of memory used by this program is related to the number of
69 sites in the current region. If the vector point map is very dense
70 (i.e., contains many data points), the program may not be able to get
71 all the memory it needs from the system. The time required to execute
72 is related to the resolution of the current region, after an initial
73 delay determined by the time taken to read the input sites file.
74 If the user has a mask set, then interpolation is only done for those
76 cells that fall within the mask. However, all sites in the current
77 region are used even if they fall outside the mask. Sites outside the
78 current region are not used in the interpolation. A larger region may
79 be set and a mask used to limit interpolation to a smaller area if it
80 is desired to use sites from outside the region in the interpolation.
81 The -n flag may also be used to achieve a similar result.
82 If more than count sites fall into one target raster cell, the mean of
84 all the site values will determine the cell value (unless the -n flag
85 is specifed, in which case only the count sites closest to the centre
86 of the cell will be interpolated).
87 By setting npoints=1, the module can be used to calculate raster
89 Voronoi diagrams (Thiessen polygons).
90
92 d.vect
93 g.region
94 r.surf.contour
95 r.surf.idw
96 r.surf.idw2
97 r.surf.gauss
98 r.surf.fractal
99 r.surf.random
100 v.surf.rst
101
103 Michael Shapiro, U.S. Army Construction Engineering Research Laboratory
104 Improved algorithm (indexes points according to cell and ignores points
105 outside current region) by Paul Kelly
106 Last changed: $Date: 2006-04-20 23:31:24 +0200 (Thu, 20 Apr 2006) $
108 Full index
110 © 2003-2008 GRASS Development Team
112GRASS 6.3.0 v.surf.idw(1)