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<h2>DESCRIPTION</h2>
<em>v.external</em> creates new vector as a link to external
<a href="http://www.gdal.org/ogr/">OGR</a> layer.
OGR (Simple Features Library) is part of the
<a href="http://www.gdal.org">GDAL</a> library, so you need to
install GDAL to use <em>v.external</em> and external OGR layers.
<P>
<h3>Supported OGR Vector Formats</h3>
<a href="http://www.gdal.org/ogr/drv_shapefile.html">ESRI
Shapefile</a><br>
<a href="http://www.gdal.org/ogr/drv_mitab.html">Mapinfo File</a>
<p>
Further available drivers such as UK .NTF, SDTS, TIGER, IHO S-57 (ENC),
DGN, GML, AVCBin, REC, Memory, OGDI, and PostgreSQL depend on the local
installation (OGR library), for details see
<a href="http://www.gdal.org/ogr/ogr_formats.html">OGR web site</a>.
<h2>EXAMPLES</h2>
<B>SHAPE files</B><BR>
<b>v.external dsn=</b><em>/home/user/shape_data</em>
<b>layer=</b><em>test_shape</em> <b>output=</b><em>grass_map</em> <br>
<P>
<B>MapInfo files</B><BR>
<b>v.external dsn=</b><em>./</em> <b>layer=</b><em>mapinfo_test</em>
<b>output=</b><em>grass_map</em>
<P>
<B>SDTS files</B> (you have to select the CATD file)<BR>
<b>v.external dsn=</b><em>CITXCATD.DDF</em> <b>output=</b><em>cities</em>
<P>
<B>TIGER files</B><BR>
<b>v.external dsn=</b><em>input/2000/56015/</em>
<b>layer=</b><em>CompleteChain,PIP</em> <b>output=</b><em>t56015_all</em>
<P>
<B>PostGIS maps (area example)</B><BR>
<b>v.external dsn=</b><em>"PG:host=localhost user=postgres dbname=postgis"</em>
<b>layer=</b><em>polymap</em> <b>output=</b><em>polygons</em>
<P>
<H2>NOTES</H2>
The simple feature data model used by OGR is very different from
the topological format used by GRASS. Instead of true topology,
so called 'pseudo topology' is created for data linked by v.external.
User should learn the difference between those to formats, because
some modules working correctly with GRASS native data,
can produce wrong results with input layers created by v.external.
<H2>REFERENCES</H2>
<a href="http://www.gdal.org/ogr/">OGR vector library</a>
<br>
<a href="http://www.gdal.org/ogr/ogr__api_8h.html">OGR vector library C API</a>
documentation
<h2>SEE ALSO</h2>
<em><a HREF="v.clean.html">v.clean</a></em>,
<em><a HREF="v.in.db.html">v.in.db</a></em>,
<em><a HREF="v.in.ogr.html">v.in.ogr</a></em>,
<em><a HREF="v.out.ogr.html">v.out.ogr</a></em>
<h2>AUTHOR</h2>
Radim Blazek, ITC-Irst, Trento, Italy
<p><i>Last changed: $Date: 2005/07/15 07:55:07 $</i>
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