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) $

       Full index

       © 2003-2013 GRASS Development Team