## DESCRIPTION

This module creates an output raster map centered on the x,y values specified with the coordinate parameter, out to the edge of the current region. The output cell values increase linearly from the specified center. The min and max parameters control the inner and outer output raster map radii, respectively.

The mult parameter can be used to multiply the output raster cells by a common factor. Note that this parameter does not affect the output raster position or size; only the z-values are changed with this parameter.

Binary-output raster maps (solid circles of one value) can be created with the -b flag. Raster maps so created can be used to create binary filters for use in i.ifft (inverse Fourier transformations; apply filter with r.mask).

## EXAMPLES

Generate a raster circle at current map center with a radius of 300m and outwardly increasing raster values:

    EASTCENTER=`g.region -c |  awk ' /center easting:/ { print $3 }'`
    NORTHCENTER=`g.region -c | awk ' /center northing:/ { print $3 }'`
    r.circle output=circle coordinate=${EASTCENTER},${NORTHCENTER} max=300

Generate a binary raster ring around current map center with an inner radius of 500m and an outer radius of 1000m:

    EASTCENTER=`g.region -c |  awk ' /center easting:/ { print $3 }'`
    NORTHCENTER=`g.region -c | awk ' /center northing:/ { print $3 }'`
    r.circle -b output=circle coordinate=${EASTCENTER},${NORTHCENTER} min=500 max=1000

## SEE ALSO

g.region, g.remove, g.rename, i.fft, i.ifft, r.mask

## AUTHORS

Bill Brown, U.S. Army Construction Engineering Research Laboratory
Additional flag/min/max parameter by Markus Neteler, University of Hannover