GSP
Quick Navigator

Search Site

Unix VPS
A - Starter
B - Basic
C - Preferred
D - Commercial
MPS - Dedicated
Previous VPSs
* Sign Up! *

Support
Contact Us
Online Help
Handbooks
Domain Status
Man Pages

FAQ
Virtual Servers
Pricing
Billing
Technical

Network
Facilities
Connectivity
Topology Map

Miscellaneous
Server Agreement
Year 2038
Credits
 

USA Flag

 

 

Man Pages
v.external(1) Grass User's Manual v.external(1)

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

vector, import, external, OGR, PostGIS, level1

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

-o
 
Override projection check (use current location’s projection)
 
Assume that the dataset has the same projection as the current location
-j
 
Perform projection check only and exit
-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
 
Advantageous when handling a large number of points
--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

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
 
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
where=sql_query
 
WHERE conditions of SQL statement without ’where’ keyword
 
Example: income < 1000 and population >= 10000
output=name
 
Name for output GRASS vector map (default: input layer)

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).

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.
Limitations:
Due to these data model differences v.external does not work with all data formats. In general, for all formats that do not have a key column (e.g. SHAPE file), attributes are not accessible, and attributes would get lost when modifying the geometries. Therefore it is generally not safe to link vector data with v.external. In many cases it does not make sense to use v.external linked data with simple features, instead vector data should be imported with v.import or v.in.ogr to get true topology support. Importantly, point cloud data which do not have topology, can be linked with v.external as long as there are no attributes attached to these point cloud data, or if the format of the point cloud data has a key column that allows linking vector geometries to attributes.
See v.db.connect for an example of maintaining attributes in external DBMS in also writable mode.

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

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

By default, PostGIS links are 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.
List of layers for given data source can be printed by -l flag.
 
v.external input="PG:host=localhost user=postgres dbname=postgis" -l
...
polymap
...
 
v.external input="PG:host=localhost user=postgres dbname=postgis" layer=polymap
Note: Authentication details (user password) can be preferably defined by db.login.

Assuming that ’mapinfo_test’ MapInfo file is located in the current directory (".").
 
v.external input=./ layer=mapinfo_test output=grass_map

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

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

By where option only subset of features can be linked. In the example below only one feature (in this case a vector tile) will be linked as a new GRASS vector map.
 
v.external in="PG:dbname=tiles" layer=wrs2_descending where="pr=191026"
...
Number of areas: 1
...

OGR vector library C API documentation

v.external.out, v.clean, v.db.connect, v.import, v.in.db, v.in.ogr, v.out.ogr
GDAL Library
 
PostGIS
See also GRASS user wiki page for more examples.

Radim Blazek, ITC-Irst, Trento, Italy
 
PostGIS support by Martin Landa, GeoForAll (OSGeoREL) Lab, Czech Technical University in Prague, Czech Republic
Last changed: $Date: 2017-11-18 09:57:44 +0100 (Sat, 18 Nov 2017) $

Available at: v.external source code (history)
Main index | Vector index | Topics index | Keywords index | Graphical index | Full index
© 2003-2018 GRASS Development Team, GRASS GIS 7.4.3 Reference Manual
GRASS 7.4.3

Search for    or go to Top of page |  Section 1 |  Main Index

Powered by GSP Visit the GSP FreeBSD Man Page Interface.
Output converted with ManDoc.