1r.surf.contour(1)           GRASS GIS User's Manual          r.surf.contour(1)
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NAME

6       r.surf.contour   -  Generates  surface  raster map from rasterized con‐
7       tours.
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KEYWORDS

10       raster, surface, interpolation
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SYNOPSIS

13       r.surf.contour
14       r.surf.contour --help
15       r.surf.contour input=name output=name  [--overwrite]  [--help]  [--ver‐
16       bose]  [--quiet]  [--ui]
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18   Flags:
19       --overwrite
20           Allow output files to overwrite existing files
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22       --help
23           Print usage summary
24
25       --verbose
26           Verbose module output
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28       --quiet
29           Quiet module output
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31       --ui
32           Force launching GUI dialog
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34   Parameters:
35       input=name [required]
36           Name of input raster map containing contours
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38       output=name [required]
39           Name for output raster map
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DESCRIPTION

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).
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48       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.
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61   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).
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67       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.
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72       An existing MASK raster map is respected for  both  reading  input  and
73       writing output.
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NOTES

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.
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86       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.
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EXAMPLE

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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SEE ALSO

115         r.mapcalc,  r.slope.aspect,  r.surf.idw,  wxGUI   vector   digitizer,
116       v.surf.idw, v.surf.rst, v.to.rast
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118       Overview: Interpolation and Resampling in GRASS GIS
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AUTHOR

121       Chuck Ehlschlaeger, U.S. Army Construction Engineering Research Labora‐
122       tory
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SOURCE CODE

125       Available at: r.surf.contour source code (history)
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127       Main index | Raster index | Topics index | Keywords index  |  Graphical
128       index | Full index
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130       © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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134GRASS 7.8.5                                                  r.surf.contour(1)
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