NAME

       v.external   -  Creates  a  new pseudo-vector map as a link to an OGR-supported layer or a
       PostGIS feature table.

KEYWORDS

       vector, import, external, OGR, PostGIS

SYNOPSIS

       v.external
       v.external --help
       v.external  [-fltb]  input=string  layer=name   [output=name]    [--overwrite]    [--help]
       [--verbose]  [--quiet]  [--ui]

   Flags:
       -f
           List supported formats and exit

       -l
           List available layers in data source and exit

       -t
           List available layers including feature type in data source and exit
           Format: layer name,type,projection check,geometry

       -b
           Do not build topology

       --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=string [required]
           Name of input OGR or PostGIS data source
           Examples:
           ESRI Shapefile: directory containing a shapefile
           MapInfo File: directory containing a mapinfo file
           PostGIS database: connection string, eg. ’PG:dbname=db user=grass’

       layer=name [required]
           Name of OGR layer or PostGIS feature table to be linked
           Examples:
           ESRI Shapefile: shapefile name
           MapInfo File: mapinfo file name
           PostGIS database: table name

       output=name
           Name for output GRASS vector map (default: input layer)

DESCRIPTION

       v.external  creates  new  vector  map  as  a link to external OGR layer or PostGIS feature
       table. OGR (Simple Features Library) is part of the GDAL library, so you need  to  install
       GDAL  to  use v.external for external OGR layers. Note that a PostGIS feature table can be
       linked also using built-in GRASS-PostGIS data driver (requires  GRASS  to  be  built  with
       PostgreSQL support).

   Supported OGR vector formats
       To list supported OGR formats, type
       v.external -f
       For details see OGR web site.

EXAMPLES

   ESRI Shapefile
       Assuming that ’test_shape.shp’ is located in directory ’/home/user/shape_data’.
       v.external input=/home/user/shape_data layer=test_shape output=grass_map

   MapInfo files
       v.external input=./ layer=mapinfo_test output=grass_map

   SDTS files
       Note: you have to select the CATD file
       v.external input=CITXCATD.DDF output=cities

   TIGER files
       v.external input=input/2000/56015/ layer=CompleteChain,PIP output=t56015_all

   PostGIS layers
       PostGIS  links are by default created by built-in PostGIS support, ie. using GRASS-PostGIS
       data driver. If the environment variable GRASS_VECTOR_OGR exists,  or  GRASS  is  compiled
       without PostgreSQL support then GRASS will use OGR-PostgreSQL driver for creating a link.
       v.external input="PG:host=localhost user=postgres dbname=postgis" layer=polymap

NOTES

       The  simple  feature  data  model  used  by  OGR  (or  PostGIS) 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 two
       formats, because some modules working correctly with GRASS native data, can produce  wrong
       results with input vector maps created by v.external.

       See  v.db.connect  for  an  example  of  maintaining  attributes  in external DBMS in also
       writable mode.

REFERENCES

       OGR vector library C API documentation

SEE ALSO

        v.external.out, v.clean, v.db.connect, v.import, v.in.db, v.in.ogr, v.out.ogr

       OGR Library
       PostGIS

       See also GRASS user wiki page for more examples.

AUTHORS

       Radim Blazek, ITC-Irst, Trento, Italy
       PostGIS support by Martin Landa, Czech Technical University in Prague, Czech Republic

       Last changed: $Date: 2016-01-13 10:20:46 +0100 (Wed, 13 Jan 2016) $

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