## NAME

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

## KEYWORDS

raster, surface, contours, vector

## SYNOPSIS

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

### Flags:

-t
  Do not create attribute table
--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
output=name [required]
  Name for output vector map
step=float
  Increment between contour levels
levels=float[,float,...]
  List of contour levels
minlevel=float
  Minimum contour level
maxlevel=float
  Maximum contour level
cut=integer
  Minimum number of points for a contour line (0 -> no limit)
  Default: 2

## DESCRIPTION

r.contour produces a vector map of specified contours from input 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 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.

## EXAMPLES

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

For an example of using levels with r.contour this example uses the elevation map from the North Carolina database:

    g.region raster=elevation
    r.contour in=elevation out=contours levels=60,90,120,150 --o
    d.mon wx0
    d.rast elevation_shade
    d.vect contours color=red

Contour lines shown on shaded terrain map

For an example of using steps with r.contour this example uses the LiDAR data derived elevation map from the North Carolina database:

    g.region raster=elev_lid792_1m -p
    r.contour input=elev_lid792_1m output=elev_lid792_1m_contours \
              minlevel=100 maxlevel=150 step=10

## AUTHORS

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

## SOURCE CODE

Available at: r.contour source code (history)

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