NAME¶

r.to.vect - Converts a raster map into a vector map.

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.

Point conversion¶

The r.to.vect program extracts data from a GRASS raster map layer and stores output in a new GRASS vector file.

Line conversion¶

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.

Area conversion¶

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.

EXAMPLES¶

The examples are based on the North Carolina sample dataset: Conversion of raster points to vector points: Random sampling of points: g.region rast=elevation -p # random sampling of points (note that r.random also writes vector points) r.random elevation raster_output=elevrand1000 n=1000 r.to.vect input=elevrand1000 output=elevrand1000 feature=point # univariate statistics of sample points v.univar elevrand1000 column=value type=point # compare to univariate statistics on original full raster map r.univar elevation Conversion of raster lines to vector lines: Vectorization of streams in watershed basins map: g.region rast=elevation -p r.watershed elev=elevation stream=elev.streams thresh=50000 r.to.vect -s input=elev.streams output=elev_streams feature=line # drop "label" column which is superfluous in this example v.db.dropcol map=elev_streams column=label v.db.renamecol map=elev_streams column=value,basin_id # report length per basin ID v.report map=elev_streams option=length units=meters Conversion of raster polygons to vector polygons: Vectorization of simplified landuse class map: g.region rast=landclass96 -p # we smooth corners of area features r.to.vect -s input=landclass96 output=my_landclass96 feature=area v.colors my_landclass96 color=random # show colorized vector map d.mon x0 d.vect my_landclass96 -a

BUGS¶

For feature=line the input raster map MUST be thinned by r.thin; if not, r.to.vect may crash.

SEE ALSO¶

g.region, r.thin, v.clean

AUTHORS¶

Point support Bill Brown Line support Mike Baba DBA Systems, Inc. 10560 Arrowhead Drive Fairfax, Virginia 22030 Area support 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: 2014-01-03 19:40:22 +0100 (Fri, 03 Jan 2014) $ Full index © 2003-2014 GRASS Development Team