r.surf.contour(1)

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

6       r.surf.contour  - Surface generation program from rasterized contours.
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KEYWORDS

9       raster
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SYNOPSIS

12       r.surf.contour
13       r.surf.contour help
14       r.surf.contour [-fs] input=string output=string  [--overwrite]
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16   Flags:
17       -f  Unused;  retained  for  compatibility  purposes, will be removed in
18           future
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20       -s  Invoke slow, but memory frugal  operation  (generally  not  needed,
21           will be removed in future)
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23       --overwrite
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25   Parameters:
26       input=string
27           Name of existing raster map containing contours
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29       output=string
30           Output elevation raster map
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DESCRIPTION

33       r.surf.contour creates a raster elevation map from a rasterized contour
34       map.  Elevation values are determined using  procedures  similar  to  a
35       manual  methods.   To  determine  the elevation of a point on a contour
36       map, an individual might interpolate its value from those  of  the  two
37       nearest contour lines (uphill and downhill).
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39       r.surf.contour  works in a similar way.  Initially, a vector map of the
40       contour lines is made with the elevation of each line as an  attribute.
41       When the program v.to.rast is run on the vector map, continuous "lines"
42       of rasters containing the contour line values will  be  the  input  for
43       r.surf.contour.  For  each  cell in the input map, either the cell is a
44       contour line cell (which is given that value), or a flood fill is  gen‐
45       erated from that spot until the fill comes to two unique values. So the
46       r.surf.contour algorithm linearly interpolates between  contour  lines.
47       The  flood  fill  is  not  allowed to cross over the rasterized contour
48       lines, thus ensuring that an uphill and downhill contour value will  be
49       the two values chosen.  r.surf.contour interpolates from the uphill and
50       downhill values by the true distance.
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52   Parameters:
53       input=name
54              Name of an existing raster map that contains a  set  of  initial
55              category values (i.e., some cells contain known elevation values
56              (denoting contours) while the rest contain NULL values or  zeros
57              (0)).
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59       output=name
60              Name  to  be assigned to new output raster map that represents a
61              smooth (e.g., elevation) surface generated from the known  cate‐
62              gory values in the input raster map layer.
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NOTES

65       r.surf.contour  works  well  under  the following circumstances: 1) the
66       contour lines extend to the the edge of the current region, 2) the pro‐
67       gram  is  run at the same resolution as that of the input map, 3) there
68       are no disjointed contour lines, and 4) no spot elevation data  BETWEEN
69       contour lines exist.  Spot elevations at the tops of hills and the bot‐
70       toms of depressions, on the other hand,  improve  the  output  greatly.
71       Violating  these  constraints  will  cause  non-intuitive  anomalies to
72       appear in the output map.  Run  r.slope.aspect
73        on r.surf.contour results to locate potential anomalies.
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75       The running of r.surf.contour is very sensitive to  the  resolution  of
76       rasterized  vector  map.  If multiple contour lines go through the same
77       raster, slight anomalies may occur.  The  speed  of  r.surf.contour  is
78       dependent  on how far "apart" the contour lines are from each other (as
79       measured in raster cells).  Since a flood fill algorithm is  used,  the
80       program's  running  time  will  grow  exponentially  with  the distance
81       between contour lines.
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BUGS

84       r.surf.contour has not been fully updated for NULL  support  and  still
85       considers a value of "0" to be NULL. Thus any contour lines at 0 eleva‐
86       tion (e.g. the coastline) will be ignored. In such cases converting any
87       0  values in the input map to -1 with r.mapcalc may be a suitable work-
88       around.
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90       Currently r.surf.contour will only produces CELL (integer) map  output.
91       If  you would like a finer grade output map (i.e. floating point) it is
92       recommended to multiply the input map by 100 (for example) using r.map‐
93       calc,  then  divide  the  resultant r.surf.contour output map by 100.0,
94       again with r.mapcalc.
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96       Volunteers are sought to remedy both these issues.
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AUTHOR

103       Chuck Ehlschlaeger, U.S. Army Construction Engineering Research Labora‐
104       tory
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106       Last changed: $Date: 2006/04/18 05:06:17 $
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108       Full index
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112GRASS 6.2.2                                                  r.surf.contour(1)