1r.surf.contour(1) GRASS GIS User's Manual r.surf.contour(1)
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6 r.surf.contour - Generates surface raster map from rasterized con‐
7 tours.
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10 raster, surface, interpolation
11
13 r.surf.contour
14 r.surf.contour --help
15 r.surf.contour input=name output=name [--overwrite] [--help] [--ver‐
16 bose] [--quiet] [--ui]
17 Flags:
19 --overwrite
20 Allow output files to overwrite existing files
21 --help
23 Print usage summary
24 --verbose
26 Verbose module output
27 --quiet
29 Quiet module output
30 --ui
32 Force launching GUI dialog
33 Parameters:
35 input=name [required]
36 Name of input raster map containing contours
37 output=name [required]
39 Name for output raster map
40
42 r.surf.contour creates a raster elevation map from a rasterized contour
43 map. Elevation values are determined using procedures similar to a
44 manual methods. To determine the elevation of a point on a contour
45 map, an individual might interpolate its value from those of the two
46 nearest contour lines (uphill and downhill).
47 r.surf.contour works in a similar way. Initially, a vector map of the
49 contour lines is made with the elevation of each line as an attribute.
50 When the program v.to.rast is run on the vector map, continuous "lines"
51 of rasters containing the contour line values will be the input for
52 r.surf.contour. For each cell in the input map, either the cell is a
53 contour line cell (which is given that value), or a flood fill is gen‐
54 erated from that spot until the fill comes to two unique values. So the
55 r.surf.contour algorithm linearly interpolates between contour lines.
56 The flood fill is not allowed to cross over the rasterized contour
57 lines, thus ensuring that an uphill and downhill contour value will be
58 the two values chosen. r.surf.contour interpolates from the uphill and
59 downhill values by the true distance.
60 Parameters:
62 input=name
63 Name of an existing raster map that contains a set of initial cate‐
64 gory values (i.e., some cells contain known elevation values
65 (denoting contours) while the rest contain NULL values).
66 output=name
68 Name to be assigned to new output raster map that represents a
69 smooth (e.g., elevation) surface generated from the known category
70 values in the input raster map layer.
71 An existing MASK raster map is respected for both reading input and
73 writing output.
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76 r.surf.contour works well under the following circumstances: 1) the
77 contour lines extend to the the edge of the current region, 2) the pro‐
78 gram is run at the same resolution as that of the input map, 3) there
79 are no disjointed contour lines, and 4) no spot elevation data BETWEEN
80 contour lines exist. Spot elevations at the tops of hills and the bot‐
81 toms of depressions, on the other hand, improve the output greatly.
82 Violating these constraints will cause non-intuitive anomalies to
83 appear in the output map. Run r.slope.aspect
84 on r.surf.contour results to locate potential anomalies.
85 The running of r.surf.contour is very sensitive to the resolution of
87 rasterized vector map. If multiple contour lines go through the same
88 raster, slight anomalies may occur. The speed of r.surf.contour is
89 dependent on how far "apart" the contour lines are from each other (as
90 measured in raster cells). Since a flood fill algorithm is used, the
91 program’s running time will grow exponentially with the distance
92 between contour lines.
93
95 Example to create contour lines from elevation model, then recreating
96 DEM from these contour lines along with differences analysis (North
97 Carolina sample data set):
98 g.region raster=elevation -p
99 # get minimum elevation value
100 r.univar elevation
101 # generate vector contour lines
102 r.contour input=elevation output=contours_5m step=5 minlevel=50
103 # rasterize contour lines
104 v.info -c contours_5m
105 v.to.rast input=contours_5m output=contours_5m use=attr attribute_column=level
106 # generate DEM from rasterized contour lines
107 r.surf.contour input=contours_5m output=elevation_from_cont5m
108 # calculate difference map
109 r.mapcalc "diff = elevation - elevation_from_cont5m"
110 r.colors diff color=differences
111 # analyze differences statistically
112 r.univar diff
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115 r.mapcalc, r.slope.aspect, r.surf.idw, wxGUI vector digitizer,
116 v.surf.idw, v.surf.rst, v.to.rast
117 Overview: Interpolation and Resampling in GRASS GIS
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121 Chuck Ehlschlaeger, U.S. Army Construction Engineering Research Labora‐
122 tory
123
125 Available at: r.surf.contour source code (history)
126 Main index | Raster index | Topics index | Keywords index | Graphical
128 index | Full index
129 © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
131GRASS 7.8.5 r.surf.contour(1)