NAME¶
r.to.vect - Converts a raster map into a vector map layer.
KEYWORDS¶
raster, conversion, vectorization
SYNOPSIS¶
r.to.vect
r.to.vect help
r.to.vect [-
svzbq]
input=
name
output=
name feature=
string [--
overwrite]
[--
verbose] [--
quiet]
Flags:¶
- -s
-
Smooth corners of area features
- -v
-
Use raster values as categories instead of unique sequence (CELL only)
- -z
-
Write raster values as z coordinate. Table is not created. Currently
supported only for points.
- -b
-
Do not build vector topology (use with care for massive point export)
- -q
-
Quiet - Do not show progress
- --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
- feature=string
-
Feature type
Options: point,line,area
Default: line
DESCRIPTION¶
r.to.vect scans the named
input raster map layer, extracts points,
lines or area edge features from it, converts data to GRASS vector format.
Points¶
The
r.to.vect program extracts data from a GRASS raster map layer and
stores output in a new GRASS
vector file.
Lines¶
r.to.vect assumes that the
input map has been thinned using
r.thin.
r.to.vect extracts vectors (aka, "arcs") from a raster map.
These arcs may represent linear features (like roads or streams), or may
represent area edge features (like political boundaries, or soil mapping
units).
r.thin and
r.to.vect may create excessive nodes at every junction,
and may create small spurs or "dangling lines" during the thinning
and vectorization process. These excessive nodes and spurs may be removed
using
v.clean.
Areas¶
r.to.vect 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.to.vect 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 map. (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.
r.to.vect extracts only area edges from the named raster input file. If
the raster map contains other data (i.e., line edges, or point data) the
output may be wrong.
BUGS¶
For feature=line the input raster map MUST be thinned by
r.thin; if not,
r.to.vect may crash.
AUTHOR¶
Points
Bill Brown
Lines
Mike Baba
DBA Systems, Inc.
10560 Arrowhead Drive
Fairfax, Virginia 22030
Areas
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
Update
Original r.to.sites, r.line and r.poly merged and updated to 5.7 by Radim Blazek
Last changed: $Date: 2008-05-16 21:09:06 +0200 (Fri, 16 May 2008) $
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