xenial (1) r.surf.contour.1grass.gz

NAME

       r.surf.contour  - Generates surface raster map from rasterized contours.

KEYWORDS

       raster, surface, interpolation

SYNOPSIS

       r.surf.contour
       r.surf.contour --help
       r.surf.contour input=name output=name  [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

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

       output=name [required]
           Name for output raster map

DESCRIPTION

       r.surf.contour  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).

       r.surf.contour 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 v.to.rast is run on the vector map, continuous
       "lines" of rasters containing the contour line values will be the input for r.surf.contour. 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  r.surf.contour  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.
       r.surf.contour interpolates from the uphill and downhill values by the true distance.

   Parameters:
       input=name
           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).

       output=name
           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 layer.

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

NOTES

       r.surf.contour  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 r.surf.contour results to locate potential anomalies.

       The running of r.surf.contour 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 r.surf.contour 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

       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
       v.info -c contours_5m
       v.to.rast input=contours_5m output=contours_5m use=attr attribute_column=level
       # generate DEM from rasterized contour lines
       r.surf.contour 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

SEE ALSO

        r.mapcalc, r.slope.aspect, r.surf.idw, wxGUI vector digitizer, v.surf.idw, v.surf.rst, v.to.rast

AUTHOR

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

       Last changed: $Date: 2015-05-25 21:03:44 +0200 (Mon, 25 May 2015) $

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