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 12:09:06 -0700 (Fri, 16 May 2008) $

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