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NAME  - Converts a raster map into a vector map.


       raster, conversion, geometry, vectorization

SYNOPSIS --help  [-svzbt]  input=name  output=name  type=string   [column=name]    [--overwrite]
       [--help]  [--verbose]  [--quiet]  [--ui]

           Smooth corners of area features

           Use raster values as categories instead of unique sequence (CELL only)

           Write raster values as z coordinate
           Table is not created. Currently supported only for points.

           Do not build vector topology
           Recommended for massive point conversion

           Do not create attribute table

           Allow output files to overwrite existing files

           Print usage summary

           Verbose module output

           Quiet module output

           Force launching GUI dialog

       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

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

DESCRIPTION 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  program extracts data from a GRASS raster map layer and stores output in a
       new GRASS vector file.

   Line conversion assumes that the input map has been thinned using r.thin. 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 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 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, 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.  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.


       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 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 -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 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 -s input=landclass96 output=my_landclass96 type=area
       v.colors my_landclass96 color=random


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


        g.region, r.thin, v.clean


       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
       Original, r.line and r.poly merged and updated to 5.7 by Radim Blazek

       Last changed: $Date: 2015-05-11 02:11:34 +0200 (Mon, 11 May 2015) $


       Available at: source code (history)

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       © 2003-2018 GRASS Development Team, GRASS GIS 7.4.0 Reference Manual