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NAME  - Generates surface raster map from rasterized contours.


       raster, surface, interpolation

SYNOPSIS --help  input=name  output=name   [--overwrite]   [--help]  [--verbose]  [--quiet]

           Allow output files to overwrite existing files

           Print usage summary

           Verbose module output

           Quiet module output

           Force launching GUI dialog

       input=name [required]
           Name of input raster map containing contours

       output=name [required]
           Name for output raster map

DESCRIPTION creates a raster elevation map from a rasterized  contour  map.   Elevation
       values  are  determined  using  procedures  similar to a manual methods.  To determine the
       elevation of a point on a contour map, an individual  might  interpolate  its  value  from
       those of the two nearest contour lines (uphill and downhill).  works  in  a similar way.  Initially, a vector map of the contour lines is
       made with the elevation of each line as an attribute.  When the program  is  run
       on  the  vector map, continuous "lines" of rasters containing the contour line values will
       be the input for For each cell in the input map,  either  the  cell  is  a
       contour line cell (which is given that value), or a flood fill is generated from that spot
       until the fill comes to two  unique  values.  So  the  algorithm  linearly
       interpolates  between  contour  lines.  The  flood  fill  is not allowed to cross over the
       rasterized contour lines, thus ensuring that an uphill and downhill contour value will  be
       the two values chosen. interpolates from the uphill and downhill values by
       the true distance.

           Name of an existing raster map that contains a set of initial category  values  (i.e.,
           some  cells  contain known elevation values (denoting contours) while the rest contain
           NULL values).

           Name to be assigned  to  new  output  raster  map  that  represents  a  smooth  (e.g.,
           elevation)  surface  generated  from the known category values in the input raster map

       An existing MASK raster map is respected for both reading input and writing output.

NOTES works well under the following circumstances: 1) the contour  lines  extend
       to  the  the  edge  of the current region, 2) the program is run at the same resolution as
       that of the input map, 3) there are no disjointed contour lines, and 4) no spot  elevation
       data BETWEEN contour lines exist.  Spot elevations at the tops of hills and the bottoms of
       depressions, on the other hand, improve the output greatly.  Violating  these  constraints
       will cause non-intuitive anomalies to appear in the output map.  Run  r.slope.aspect
        on results to locate potential anomalies.

       The  running  of  is very sensitive to the resolution of rasterized vector
       map.  If multiple contour lines go through the same raster, slight  anomalies  may  occur.
       The  speed  of  is dependent on how far "apart" the contour lines are from
       each other (as measured in raster cells).  Since a  flood  fill  algorithm  is  used,  the
       program’s running time will grow exponentially with the distance between contour lines.


       Example  to  create  contour  lines  from  elevation model, then recreating DEM from these
       contour lines along with differences analysis (North Carolina sample data set):
       g.region raster=elevation -p
       # get minimum elevation value
       r.univar elevation
       # generate vector contour lines
       r.contour input=elevation output=contours_5m step=5 minlevel=50
       # rasterize contour lines -c contours_5m input=contours_5m output=contours_5m use=attr attribute_column=level
       # generate DEM from rasterized contour lines input=contours_5m output=elevation_from_cont5m
       # calculate difference map
       r.mapcalc "diff = elevation - elevation_from_cont5m"
       r.colors diff color=differences
       # analyze differences statistically
       r.univar diff


        r.mapcalc, r.slope.aspect,, wxGUI vector  digitizer,,,

       Overview: Interpolation and Resampling in GRASS GIS


       Chuck Ehlschlaeger, U.S. Army Construction Engineering Research Laboratory

       Last changed: $Date: 2016-08-03 13:50:26 +0200 (Wed, 03 Aug 2016) $


       Available at: source code (history)

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