NAME

       r.contour  - Produces a vector map of specified contours from a raster map.

KEYWORDS

       raster, DEM, contours, vector

SYNOPSIS

       r.contour
       r.contour help
       r.contour  [-qn]  input=name  output=name   [levels=float[,float,...]]    [minlevel=float]
       [maxlevel=float]   [step=float]   [cut=integer]   [--overwrite]  [--verbose]  [--quiet]

   Flags:
       -q
           Run quietly

       -n
           Suppress single crossing error messages

       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name
           Name of input raster map

       output=name
           Name for output vector map

       levels=float[,float,...]
           List of contour levels

       minlevel=float
           Minimum contour level

       maxlevel=float
           Maximum contour level

       step=float
           Increment between contour levels

       cut=integer
           Minimum number of points for a contour line (0 -> no limit)
           Default: 0

DESCRIPTION

       r.contour produces a GRASS binary vector map of specified contours  from  a  GRASS  raster
       map.   Contours  can  be  produced using a comma-separated list of values in levels, or at
       some regular increment using the step parameter, using minlevel and  maxlevel  as  minimum
       and  maximum  contour  values,  respectively. If no minlevel or maxlevel is specified, the
       minimum and maximum cell values in the input raster map will be used.

NOTES

       r.contour will either step through incremental contours or produce contours from a list of
       levels,  not  both.  If  both  a list of levels and a step are specified, the list will be
       produced and the step will be ignored.

       Zero is treated as a valid data value by r.contour.

       If a contour level exactly matches a category value in the raster map,  the  contour  line
       may  backtrack  on  itself, causing illegal arcs to be produced in the output GRASS vector
       map.

       The optional cut parameter allows the user to specify a minimum  number  of  raster  cells
       eligilble  to be included in a contour line written to the output vector map. It acts like
       a filter, omitting spurs, single points, etc., making the output more generalized.

EXAMPLE

       In the Spearfish location, produce a vector contour map from  input  raster  elevation.dem
       with  contour  levels  from  1000m to 2000m, 100m contour step, and a minimum of 200 input
       raster  points  contributing  to   the   contour   line:   r.contour   input=elevation.dem
       output=elevation_dem_contours minlevel=1000 maxlevel=2000 step=100 cut=200

AUTHORS

       Terry Baker, U.S. Army Construction Engineering Research Laboratory
       3/2001: cut parameter and fixes by Andrea Aime (aaime@libero.it)

       Last changed: $Date: 2008-05-16 12:09:06 -0700 (Fri, 16 May 2008) $

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