v.surf.idw(1grass) | Grass User's Manual | v.surf.idw(1grass) |
v.surf.idw - Provides surface interpolation from vector point data by Inverse Distance Squared Weighting.
vector, surface, interpolation, IDW
v.surf.idw
v.surf.idw --help
v.surf.idw [-n] input=name
[layer=string] [column=name]
output=name [npoints=count]
[power=float] [--overwrite] [--help]
[--verbose] [--quiet] [--ui]
v.surf.idw fills a raster matrix with interpolated values generated from a set of irregularly spaced vector 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.
Values to interpolate are read from column option. If this option is not given than the program uses categories as values to interpolate or z-coordinates if the input vector map is 3D.
The amount of memory used by this program is related to the number of vector points in the current region. If the vector point map is very dense (i.e., contains many data points), the program may not be able to get all the memory it needs from the system. The time required to execute is related to the resolution of the current region, after an initial delay determined by the time taken to read the input vector points map.
Note that vector features without category in given layer are skipped.
If the user has a mask set, then interpolation is only done for those cells that fall within the mask. The module has two separate modes of operation for selecting the vector points that are used in the interpolation:
The power parameter defines an exponential distance weight. Greater values assign greater influence to values closer to the point to be interpolated. The interpolation function peaks sharply over the given data points for 0 < p < 1 and more smoothly for larger values. The default value for the power parameter is 2.
By setting npoints=1, the module can be used to calculate raster Voronoi diagrams (Thiessen polygons).
g.region, r.surf.contour, r.surf.idw, r.surf.gauss, r.surf.fractal, r.surf.random, v.surf.rst
Overview: Interpolation and Resampling in GRASS GIS
Michael Shapiro, U.S. Army Construction Engineering Research
Laboratory
Improved algorithm (indexes points according to cell and ignores points
outside current region) by Paul Kelly
Last changed: $Date: 2016-08-03 13:50:26 +0200 (Wed, 03 Aug 2016) $
Available at: v.surf.idw source code (history)
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