v.externalgrass - Online in the Cloud

PROGRAM:

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

Use v.externalgrass online using onworks.net services