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]  [--ver‐
15       bose]  [--quiet]
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17   Flags:
18       -f
19           Unused; retained for compatibility purposes,  will  be  removed  in
20           future
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22       -s
23           Invoke  slow,  but  memory  frugal operation (generally not needed,
24           will be removed in future)
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26       --overwrite
27           Allow output files to overwrite existing files
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29       --verbose
30           Verbose module output
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32       --quiet
33           Quiet module output
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35   Parameters:
36       input=string
37           Name of existing raster map containing contours
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39       output=string
40           Output elevation raster map
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DESCRIPTION

43       r.surf.contour creates a raster elevation map from a rasterized contour
44       map.   Elevation  values  are  determined using procedures similar to a
45       manual methods.  To determine the elevation of a  point  on  a  contour
46       map,  an  individual  might interpolate its value from those of the two
47       nearest contour lines (uphill and downhill).
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49       r.surf.contour works in a similar way.  Initially, a vector map of  the
50       contour  lines is made with the elevation of each line as an attribute.
51       When the program v.to.rast is run on the vector map, continuous "lines"
52       of  rasters  containing  the  contour line values will be the input for
53       r.surf.contour. For each cell in the input map, either the  cell  is  a
54       contour  line cell (which is given that value), or a flood fill is gen‐
55       erated from that spot until the fill comes to two unique values. So the
56       r.surf.contour  algorithm  linearly interpolates between contour lines.
57       The flood fill is not allowed to  cross  over  the  rasterized  contour
58       lines,  thus ensuring that an uphill and downhill contour value will be
59       the two values chosen.  r.surf.contour interpolates from the uphill and
60       downhill values by the true distance.
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62   Parameters:
63       input=name
64              Name  of  an  existing raster map that contains a set of initial
65              category values (i.e., some cells contain known elevation values
66              (denoting  contours) while the rest contain NULL values or zeros
67              (0)).
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69       output=name
70              Name to be assigned to new output raster map that  represents  a
71              smooth  (e.g., elevation) surface generated from the known cate‐
72              gory values in the input raster map layer.
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NOTES

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

94       r.surf.contour  has  not  been fully updated for NULL support and still
95       considers a value of "0" to be NULL. Thus any contour lines at 0 eleva‐
96       tion (e.g. the coastline) will be ignored. In such cases converting any
97       0 values in the input map to -1 with r.mapcalc may be a suitable  work-
98       around.
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100       Currently  r.surf.contour  will only produce CELL (integer) map output.
101       If you would like a finer grade output map (i.e. floating point) it  is
102       recommended  to  multiply  the  input  map  by 1000 (for example) using
103       r.mapcalc, then divide  the  resultant  r.surf.contour  output  map  by
104       1000.0, again with r.mapcalc.
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106       Volunteers are sought to remedy both these issues.
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AUTHOR

113       Chuck Ehlschlaeger, U.S. Army Construction Engineering Research Labora‐
114       tory
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116       Last changed: $Date: 2007-02-06 07:48:36 +0100 (Tue, 06 Feb 2007) $
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118       Full index
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120       © 2003-2008 GRASS Development Team
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124GRASS 6.3.0                                                  r.surf.contour(1)