1r.surf.idw(1) Grass User's Manual r.surf.idw(1)
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6 r.surf.idw - Provides surface interpolation from raster point data by
7 Inverse Distance Squared Weighting.
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10 raster, surface, interpolation, IDW
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13 r.surf.idw
14 r.surf.idw --help
15 r.surf.idw [-e] input=name output=name [npoints=integer] [--over‐
16 write] [--help] [--verbose] [--quiet] [--ui]
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18 Flags:
19 -e
20 Output is the interpolation error
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22 --overwrite
23 Allow output files to overwrite existing files
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25 --help
26 Print usage summary
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28 --verbose
29 Verbose module output
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31 --quiet
32 Quiet module output
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34 --ui
35 Force launching GUI dialog
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37 Parameters:
38 input=name [required]
39 Name of input raster map
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41 output=name [required]
42 Name for output raster map
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44 npoints=integer
45 Number of interpolation points
46 Default: 12
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49 r.surf.idw fills a grid cell (raster) matrix with interpolated values
50 generated from input raster data points. It uses a numerical approxima‐
51 tion technique based on distance squared weighting of the values of
52 nearest data points. The number of nearest data points used to deter‐
53 mined the interpolated value of a cell can be specified by the user
54 (default: 12 nearest data points).
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56 If there is a current working mask, it applies to the output raster
57 map. Only those cells falling within the mask will be assigned interpo‐
58 lated values. The search procedure for the selection of nearest neigh‐
59 boring points will consider all input data, without regard to the mask.
60 The -e flag is the error analysis option that interpolates values only
61 for those cells of the input raster map which have non-zero values and
62 outputs the difference (see NOTES below).
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64 The npoints parameter defines the number of nearest data points used to
65 determine the interpolated value of an output raster cell.
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68 r.surf.idw is a surface generation utility which uses inverse distance
69 squared weighting (as described in Applied Geostatistics by E. H.
70 Isaaks and R. M. Srivastava, Oxford University Press, 1989) to assign
71 interpolated values. The implementation includes a customized data
72 structure somewhat akin to a sparse matrix which enhances the effi‐
73 ciency with which nearest data points are selected. For latitude/lon‐
74 gitude projections, distances are calculated from point to point along
75 a geodesic.
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77 Unlike r.surf.idw2 (addon), which processes all input data points in
78 each interpolation cycle, r.surf.idw attempts to minimize the number of
79 input data for which distances must be calculated. Execution speed is
80 therefore a function of the search effort, and does not increase appre‐
81 ciably with the number of input data points.
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83 r.surf.idw will generally outperform r.surf.idw2 except when the input
84 data layer contains few non-zero data, i.e. when the cost of the search
85 exceeds the cost of the additional distance calculations performed by
86 r.surf.idw2. The relative performance of these utilities will depend on
87 the comparative speed of boolean, integer and floating point operations
88 on a particular platform.
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90 Worst case search performance by r.surf.idw occurs when the interpo‐
91 lated cell is located outside of the region in which input data are
92 distributed. It therefore behooves the user to employ a mask when geo‐
93 graphic region boundaries include large areas outside the general
94 extent of the input data.
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96 The degree of smoothing produced by the interpolation will increase
97 relative to the number of nearest data points considered. The utility
98 may be used with regularly or irregularly spaced input data. However,
99 the output result for the former may include unacceptable nonconformi‐
100 ties in the surface pattern.
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102 The -e flag option provides a standard surface-generation error analy‐
103 sis facility. It produces an output raster map of the difference of
104 interpolated values minus input values for those cells whose input data
105 are non-zero. For each interpolation cycle, the known value of the cell
106 under consideration is ignored, and the remaining input values are used
107 to interpolate a result. The output raster map may be compared to the
108 input raster map to analyze the distribution of interpolation error.
109 This procedure may be helpful in choosing the number of nearest neigh‐
110 bors considered for surface generation.
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113 Module r.surf.idw works only for integer (CELL) raster maps.
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116 r.surf.contour, r.surf.gauss, r.surf.fractal, r.surf.random,
117 v.surf.idw, v.surf.rst
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119 Overview: Interpolation and Resampling in GRASS GIS
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122 Greg Koerper
123 Global Climate Research Project
124 U.S. EPA Environmental Research Laboratory
125 200 S.W. 35th Street, JSB
126 Corvallis, OR 97333
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128 Last changed: $Date: 2017-01-05 08:56:15 +0100 (Thu, 05 Jan 2017) $
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131 Available at: r.surf.idw source code (history)
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133 Main index | Raster index | Topics index | Keywords index | Graphical
134 index | Full index
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136 © 2003-2019 GRASS Development Team, GRASS GIS 7.4.4 Reference Manual
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140GRASS 7.4.4 r.surf.idw(1)