1r.bilinear(1) Grass User's Manual r.bilinear(1)
2
6 r.bilinear - Bilinear interpolation utility for raster map layers.
7
9 raster
10
12 r.bilinear
13 r.bilinear help
14 r.bilinear input=name output=name [north=float] [east=float]
15 [--overwrite]
16 Flags:
18 --overwrite
19 Parameters:
21 input=name
22 Name of input raster map
23 output=name
25 Name for output raster map
26 north=float
28 specific input value to be assigned to the north and/or south poles
29 for longitude-latitude grids
30 east=float
32 specific input value to be assigned to the north and/or south poles
33 for longitude-latitude grids
34
36 r.bilinear fills a grid cell (raster) matrix with interpolated values
37 generated from a set of input layer data points. It uses the bilinear
38 interpolation method, a simple algorithm usually applied only to com‐
39 pletely defined raster areas (input data void of null data values).
40 Here the values of 4 input cells are used to define an interpolation
41 function of constant gradient within each rectangular area defined by
42 the cell centers. User should be aware that the gradient of the inter‐
43 polation functions changes discontinuously across lines intersecting
44 the cell centers of the input raster.
45 If there is a current working mask, it applies to the output raster
47 file. Only those cells falling within the mask will be assigned inter‐
48 polated values. The procedure for selection of input data will con‐
49 sider all input data relevant to interpolating values at the cell cen‐
50 ters of the current geographic region, ignoring the curent mask. Note
51 that cells of the output raster that cannot be bounded by 4 input cell
52 centers are set to null.
53
55 The north and south parameters have been included to allow for specific
56 input values to be assigned to the north and/or south poles for longi‐
57 tude-latitude grids. These data, if included, are used to interpolate
58 values for cells that are north or south of a line intersecting the
59 cell centers of the first or last row of input, respectively. When
60 utilized, the interpolation procedure will be continuous from the north
61 and/or south boundary of the current geographic region. This option is
62 necessary, since the data structure defining a raster will not allow
63 for data to be assigned to a cell centered at 90N or 90S. By including
64 the option, the user can create output surfaces that are continuous
65 between the poles. The interpolation will be "wrap-around" from west
66 to east (across latitude) only if the input raster has an east edge
67 identical to its west edge.
68 For longitude-latitude databases, the interpolation algorithm is based
70 on degree fractions, not on the absolute distances between cell cen‐
71 ters. Any attempt to implement the latter would violate the integrity
72 of the interpolation method.
73 r.bilinear may be used in some instances as an alternative to the near‐
75 est neighbor approach inherent to r.resample. Note, however, that the
76 extent of non-null data area of the output raster must be less than
77 that of the input raster. The only exception to this occurs in the
78 case where the north and south parameters are utilized for longitude-
79 latitude rasters.
80
82 r.surf.idw, r.surf.idw2, g.region, r.resample, r.resample
83
85 Greg Koerper
86 ManTech Environmental Technology, Inc.
87 Global Climate Research Project
88 U.S. EPA Environmental Research Laboratory
89 Last changed: $Date: 2003/04/30 15:17:25 $
91 Full index
93GRASS 6.2.2 r.bilinear(1)