.TH v.external 1grass "" "GRASS 6.4.4" "Grass User's Manual"
.SH NAME
\fI\fBv.external\fR\fR  - Creates a new vector as a read-only link to OGR layer.
.SH KEYWORDS
vector, external, import
.SH SYNOPSIS
\fBv.external\fR
.br
\fBv.external help\fR
.br
\fBv.external\fR [\-\fBf\fR]  [\fBdsn\fR=\fIstring\fR]   [\fBoutput\fR=\fIname\fR]   [\fBlayer\fR=\fIstring\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR] 
.SS Flags:
.IP "\fB\-f\fR" 4m
.br
List supported formats and exit
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.PP
.SS Parameters:
.IP "\fBdsn\fR=\fIstring\fR" 4m
.br
OGR datasource name. Examples:
.br
		ESRI Shapefile: directory containing shapefiles		MapInfo File: directory containing mapinfo files
.IP "\fBoutput\fR=\fIname\fR" 4m
.br
Output vector. If not given, available layers are printed only.
.IP "\fBlayer\fR=\fIstring\fR" 4m
.br
OGR layer name. If not given, available layers are printed only. Examples:
.br
		ESRI Shapefile: shapefile name		MapInfo File: mapinfo file name
.PP
.SH DESCRIPTION
\fIv.external\fR creates new vector as a link to external  
OGR layer (read only). 
OGR (Simple Features Library) is part of the 
GDAL library, so you need to
install GDAL to use \fIv.external\fR and external OGR layers.
.PP
.SS Supported OGR Vector Formats
ESRI
Shapefile
.br
Mapinfo File
.PP
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
OGR web site.
.SH EXAMPLES
\fBSHAPE files\fR
.br
\fC
.DS
.br
v.external dsn=/home/user/shape_data layer=test_shape output=grass_map 
.br
.DE
\fR
.PP
\fBMapInfo files\fR
.br
\fC
.DS
.br
v.external dsn=./ layer=mapinfo_test output=grass_map
.br
.DE
\fR
.PP
\fBSDTS files\fR (you have to select the CATD file)
.br
\fC
.DS
.br
v.external dsn=CITXCATD.DDF output=cities
.br
.DE
\fR
.PP
\fBTIGER files\fR
.br
\fC
.DS
.br
v.external dsn=input/2000/56015/ layer=CompleteChain,PIP output=t56015_all
.br
.DE
\fR
.PP
\fBPostGIS maps (area example)\fR
.br
\fC
.DS
.br
v.external dsn="PG:host=localhost user=postgres dbname=postgis" layer=polymap \(rs
.br
output=polygons
.br
.DE
\fR
.PP
.SH NOTES
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 \fIv.external\fR. 
.PP
See v.db.connect for an example of
maintaining attributes in external DBMS in also writable mode.
.SH REFERENCES
OGR vector library
.br
OGR vector library C API
documentation
.SH SEE ALSO
\fIv.clean\fR,
\fIv.db.connect\fR,
\fIv.in.db\fR,
\fIv.in.ogr\fR,
\fIv.out.ogr\fR
.SH AUTHOR
Radim Blazek, ITC-Irst, Trento, Italy
.PP
\fILast changed: $Date: 2012-02-25 14:38:11 +0100 (Sat, 25 Feb 2012) $\fR
.PP
Full index
.PP
© 2003-2014 GRASS Development Team