Ubuntu Manpage: r.to.vect - Converts a raster map into a vector map.

Provided by: grass-doc_7.0.3-1build1_all

NAME

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

KEYWORDS

       raster, conversion, geometry, vectorization

SYNOPSIS

       r.to.vect
       r.to.vect --help
       r.to.vect  [-svzbt]  input=name  output=name  type=string   [column=name]    [--overwrite]
       [--help]  [--verbose]  [--quiet]  [--ui]

   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
           Recommended for massive point conversion

       -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

       type=string [required]
           Output feature type
           Options: point, line, area

       column=name
           Name of attribute column to store value
           Name must be SQL compliant
           Default: value

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 raster=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 type=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 raster=elevation -p
       r.watershed elev=elevation stream=elev.streams thresh=50000
       r.to.vect -s input=elev.streams output=elev_streams type=line
       # drop "label" column which is superfluous in this example
       v.db.dropcolumn map=elev_streams column=label
       v.db.renamecolumn map=elev_streams column=value,basin_id
       # report length per basin ID
       v.report map=elev_streams option=length units=meters sort=asc

       Conversion of raster polygons to vector polygons:

       Vectorization of simplified landuse class map:
       g.region raster=landclass96 -p
       # we smooth corners of area features
       r.to.vect -s input=landclass96 output=my_landclass96 type=area
       v.colors my_landclass96 color=random

KNOWN ISSUES

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

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: 2015-05-11 02:16:13 +0200 (Mon, 11 May 2015) $

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