1rasterintro(1) Grass User's Manual rasterintro(1)
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6 Raster maps in general
7 The geographic boundaries of the raster file are described by the
8 north, south, east, and west fields. These values describe the lines
9 which bound the map at its edges. These lines do NOT pass through the
10 center of the grid cells at the edge of the map, but along the edge of
11 the map itself.
12 As a general rule in GRASS:
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16 Raster output maps have their bounds and resolution equal to
17 those of the current region.
18 2
20 Raster input maps are automatically cropped/padded and rescaled
21 (using nearest-neighbour resampling) to match the current
22 region.
23 There are a few exceptions to this: r.in.* programs read the data cell-
25 for-cell, with no resampling. When reading non-georeferenced data, the
26 imported map will usually have its lower-left corner at (0,0) in the
27 location's coordinate system; ther user needs to use r.region to
28 "place" the imported map.
29 Some programs which need to perform specific types of resampling (e.g.
31 r.resamp.rst) read the input maps at their original resolution then do
32 the resampling themselves.
33 r.proj has to deal with two regions (source and destination) simultane‐
35 ously; both will have an impact upon the final result.
36 Raster import
38 The module r.in.gdal offers a common interface for many different
39 raster formats. Additionally, it also offers options such as on-the-fly
40 location creation or extension of the default region to match the
41 extent of the imported raster map. For special cases, other import
42 modules are available. Always the full map is imported.
43 For importing scanned maps, the user will need to create a x,y-loca‐
45 tion, scan the map in the desired resolution and save it into an appro‐
46 priate raster format (e.g. tiff, jpeg, png, pbm) and then use r.in.gdal
47 to import it. Based on reference points the scanned map can be recified
48 to obtain geocoded data.
49 Raster map operations
51 GRASS raster map processing is always performed in the current region
52 settings (see g.region), i.e. the current region extent and current
53 raster resolution is used. If the resolution differs from that of the
54 input raster map(s), on-the-fly resampling is performed (nearest neigh‐
55 bor resampling). If this is not desired, the input map(s) has/have to
56 be resampled beforehand with one of the dedicated modules.
57 Raster map statistics
59 A couple of commands are available to calculate local statistics
60 (r.neighbors), and global statistics (r.surf.area, r.sum). Profiles
61 and transects can be generated (r.profile, r.transect) as well as his‐
62 tograms (d.histogram) and polar diagrams (d.polar). Univariate statis‐
63 tics (r.univar) and reports are also available (r.report,<a
64 href="r.stats.html">r.stats, r.volume).
65 Raster map algebra and aggregation
67 The r.mapcalc command provides raster map algebra methods. The r.aver‐
68 age command aggregates one map based on a second map.
69 Raster map resampling and interpolation methods
71 GRASS offers various raster resampling and interpolation methods:
72 Resampling with nearest neighbor and bilinear method
74 (r.bilinear)
75 Inverse distance weighted average (IDW) interpolation
77 (r.surf.idw2)
78 Regularized spline with tension (RST) interpolation 2D
80 (r.resamp.rst)
81 Interpolating from contour lines (r.contour)
83 Hydrologic modeling toolbox
85 Watershed modeling related modules are r.basins.fill, r.water.outlet,
86 r.watershed, and r.terraflow. Water flow related modules are r.carve,
87 r.drain, r.fill.dir, r.fillnulls, r.flow, and r.topidx. Flooding can
88 be simulated with r.lake. Hydrologic simulation model are available as
89 r.sim.sediment, r.sim.water, and r.topmodel.
90 See also
92 Introduction to GRASS vector map processing
93 Introduction to GRASS 3D raster map (voxel) processing
95 full index
97GRASS 6.2.2 rasterintro(1)