NAME
r.poly - Extracts area edges from a raster map layer and converts
data to GRASS vector format.
(GRASS Raster Program)
SYNOPSIS
r.poly
r.poly help
r.poly [-lcb] input=name output=name
DESCRIPTION
r.poly scans the named input raster map
layer, extracts area edge features from it, converts data
to GRASS vector format, and smoothes vectors.
r.poly first traces the perimeter of each unique
area in the raster map layer and creates vector data to
represent it. The cell category values for the raster map
layer will be used to create attribute information for the
resultant vector area edge data.
A true vector tracing of the area edges might appear
blocky, since the vectors outline the edges of raster data
that are stored in rectangular cells. To produce a
better-looking vector map, r.poly smoothes the
corners of the vector data as they are being extracted. At
each change in direction (i.e., each corner), the two
midpoints of the corner cell (half the cell's height and
width) are taken, and the line segment connecting them is
used to outline this corner in the resultant vector file.
(The cell's cornermost node is ignored.) Because vectors
are smoothed by this program, the resulting vector map will
not be "true" to the raster map from which it was created.
The user should check the resolution of the geographic
region (and the original data) to estimate the possible
error introduced by smoothing.
OPTIONS
The user can run this program either non-interactively or
interactively. The program will be run non-interactively
if the user specifies program arguments and flag settings
on the command line using the form:
-
r.poly [-lcb] input=name output=name
Alternately, the user can simply type r.poly on the command line
without program arguments. In this case, the user will be prompted for
parameter values and flag settings using the standard GRASS
parser interface.
Flags:
- -l
- Smooth corners.
- -c
- Output values as category labels
- -b
- Output only area borders as vector lines
Parameters:
- input=name
- Use the existing raster map name as input.
- output=name
- Set the new vector output file name to name.
NOTES
r.poly extracts only area edges from the named raster input file.
If the raster file contains other data (i.e., line edges, or point data) the
output may be wrong. Using -b the area borders (vector line type)
are written instead of the areas (vector area type). This may be useful for
buffering of area borders and other analysis.
The user must run v.support
on the resultant file to build the needed
topology information stored in the dig_plus file.
SEE ALSO
v.support
parser
AUTHOR
Original version of r.poly:
Jean Ezell and Andrew Heekin,
U.S. Army Construction Engineering
Research Laboratory
Modified program for smoothed lines:
David Satnik,
Central Washington University
Updated 2001 by Andrea Aime, Modena, Italy
Last changed: $Date: 2002/01/25 05:45:34 $