Ubuntu Manpage: r.surf.contour - Surface generation program from rasterized contours.

NAME

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

KEYWORDS

       raster, interpolation

SYNOPSIS

       r.surf.contour
       r.surf.contour help
       r.surf.contour [-fs] input=string output=string  [--overwrite]  [--verbose]  [--quiet]

   Flags:
       -f
           Unused; retained for compatibility purposes, will be removed in future

       -s
           Invoke slow, but memory frugal operation (generally not needed, will be removed in future)

       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=string
           Name of existing raster map containing contours

       output=string
           Output elevation 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 rast=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 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

AUTHOR

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

       Last changed: $Date: 2012-09-18 13:39:02 -0700 (Tue, 18 Sep 2012) $

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