Working with external data in GRASS - Revision history

Neteler: remove version from GRASS (avoid "7")

2025-09-23T07:43:24Z

remove version from GRASS (avoid "7")

← Older revision		Revision as of 07:43, 23 September 2025
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	This page explains how to effectively work with external raster and vector data in GRASS 7. See also [[PostGIS]] and [[PostGIS Topology]].		This page explains how to effectively work with external raster and vector data in GRASS. See also [[PostGIS]] and [[PostGIS Topology]].
	__TOC__		__TOC__
	== Raster data ==		== Raster data ==
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	==== v.extract showcase ====		==== v.extract showcase ====

	GRASS 7 also supports write access to the external data using OGR or GRASS-PostGIS data driver. Showcase bellow:		GRASS also supports write access to the external data using OGR or GRASS-PostGIS data driver. Showcase bellow:

	{{cmd\|v.external}} input=PG:dbname=pgis_nc layer=bridges output=b		{{cmd\|v.external}} input=PG:dbname=pgis_nc layer=bridges output=b
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	[[Category:Vector]]		[[Category:Vector]]
	[[Category:FAQ]]		[[Category:FAQ]]
	~~[[Category:GRASS 7]]~~

Neteler: Neteler moved page Working with external data in GRASS 7 to Working with external data in GRASS: remove GRASS version from title

2025-09-23T07:41:29Z

Neteler moved page Working with external data in GRASS 7 to Working with external data in GRASS: remove GRASS version from title

← Older revision		Revision as of 07:41, 23 September 2025
(No difference)

⚠️NikosA: Updated link to OGR's PostgreSQL / PostGIS driver page

2018-05-08T09:15:28Z

Updated link to OGR's PostgreSQL / PostGIS driver page

← Older revision		Revision as of 09:15, 8 May 2018
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	Assuming that PostGIS layer named <tt>bridges</tt> is located in database <tt>pgis_nc</tt>. This layer is linked to GRASS mapset as vector map with name <tt>b</tt>. {{cmd\|v.external}} also builds pseudo-topology over simple features which enables GRASS to access linked vector data on level 2. Note that data are stored as simple features, so no full topology support can be build based on this data.		Assuming that PostGIS layer named <tt>bridges</tt> is located in database <tt>pgis_nc</tt>. This layer is linked to GRASS mapset as vector map with name <tt>b</tt>. {{cmd\|v.external}} also builds pseudo-topology over simple features which enables GRASS to access linked vector data on level 2. Note that data are stored as simple features, so no full topology support can be build based on this data.

	By default PostGIS feature tables are linked using built-in '''GRASS-PostGIS data driver''' - it means that PostGIS geometry data are accessed by GRASS directly without any abstract level (like OGR library). When GRASS is built without PostgreSQL support or environmental variable <tt>GRASS_VECTOR_OGR</tt> exists, then GRASS will access PostGIS data using [http://gdal.org~~/ogr~~/drv_pg.html OGR-PostgreSQL] driver.		By default PostGIS feature tables are linked using built-in '''GRASS-PostGIS data driver''' - it means that PostGIS geometry data are accessed by GRASS directly without any abstract level (like OGR library). When GRASS is built without PostgreSQL support or environmental variable <tt>GRASS_VECTOR_OGR</tt> exists, then GRASS will access PostGIS data using [http://www.gdal.org/drv_pg.html OGR-PostgreSQL] driver.

	=== Direct access to external data ===		=== Direct access to external data ===

Neteler: Updated to G7.2

2017-01-18T13:14:05Z

Updated to G7.2

← Older revision		Revision as of 13:14, 18 January 2017
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	To link ''file-based data formats'', eg. [http://gdal.osgeo.org/ogr/drv_shapefile.html ESRI Shapefile] using OGR library		To link ''file-based data formats'', eg. [http://gdal.osgeo.org/ogr/drv_shapefile.html ESRI Shapefile] using OGR library

	{{cmd\|v.external}} ~~dsn~~=ncshape/ layer=railroads		{{cmd\|v.external}} input=ncshape/ layer=railroads

	Assuming that <tt>railroads.shp</tt> is located in directory <tt>ncshape</tt>.		Assuming that <tt>railroads.shp</tt> is located in directory <tt>ncshape</tt>.
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	To link ''database-based data formats'', eg. [http://gdal.osgeo.org/ogr/drv_pg.html PostGIS] using GRASS-PostGIS data driver		To link ''database-based data formats'', eg. [http://gdal.osgeo.org/ogr/drv_pg.html PostGIS] using GRASS-PostGIS data driver

	{{cmd\|v.external}} ~~dsn~~=PG:dbname=pgis_nc -l		{{cmd\|v.external}} input=PG:dbname=pgis_nc -l

	PostGIS database <pgis_nc> contains 55 feature table(s):		PostGIS database <pgis_nc> contains 55 feature table(s):
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	...		...

	{{cmd\|v.external}} ~~dsn~~=PG:dbname=pgis_nc layer=bridges output=b		{{cmd\|v.external}} input=PG:dbname=pgis_nc layer=bridges output=b

	Assuming that PostGIS layer named <tt>bridges</tt> is located in database <tt>pgis_nc</tt>. This layer is linked to GRASS mapset as vector map with name <tt>b</tt>. {{cmd\|v.external}} also builds pseudo-topology over simple features which enables GRASS to access linked vector data on level 2. Note that data are stored as simple features, so no full topology support can be build based on this data.		Assuming that PostGIS layer named <tt>bridges</tt> is located in database <tt>pgis_nc</tt>. This layer is linked to GRASS mapset as vector map with name <tt>b</tt>. {{cmd\|v.external}} also builds pseudo-topology over simple features which enables GRASS to access linked vector data on level 2. Note that data are stored as simple features, so no full topology support can be build based on this data.
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	GRASS 7 also supports write access to the external data using OGR or GRASS-PostGIS data driver. Showcase bellow:		GRASS 7 also supports write access to the external data using OGR or GRASS-PostGIS data driver. Showcase bellow:

	{{cmd\|v.external}} ~~dsn~~=PG:dbname=pgis_nc layer=bridges output=b		{{cmd\|v.external}} input=PG:dbname=pgis_nc layer=bridges output=b

	{{cmd\|v.out.ascii}} input=b where="cat < 10" --q		{{cmd\|v.out.ascii}} input=b where="cat < 10" --q
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	{{cmd\|v.external.out}} ~~dsn~~=PG:dbname=pgis_nc format=PostgreSQL		{{cmd\|v.external.out}} input=PG:dbname=pgis_nc format=PostgreSQL

	{{cmd\|v.extract}} input=b output=b_9 where="cat < 10"		{{cmd\|v.extract}} input=b output=b_9 where="cat < 10"

	{{cmd\|v.external}} ~~dsn~~=PG:dbname=pgis_nc -l		{{cmd\|v.external}} input=PG:dbname=pgis_nc -l

	PostGIS database <pgis_nc> contains 56 feature table(s):		PostGIS database <pgis_nc> contains 56 feature table(s):
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	Check created OGR/PostGIS layer (link):		Check created OGR/PostGIS layer (link):

	{{cmd\|v.external}} ~~dsn~~=PG:dbname=pgis_nc layer=pmap		{{cmd\|v.external}} input=PG:dbname=pgis_nc layer=pmap

	{{cmd\|v.info}} -t map=pmap		{{cmd\|v.info}} -t map=pmap
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	* Export data to PostGIS database (from mapset 'sqlite')		* Export data to PostGIS database (from mapset 'sqlite')

	{{cmd\|v.out.ogr}} input=b ~~dsn~~=PG:dbname=pgis_nc format=PostgreSQL olayer=bridges --o		{{cmd\|v.out.ogr}} input=b input=PG:dbname=pgis_nc format=PostgreSQL olayer=bridges --o
	{{cmd\|v.out.ogr}} input=u ~~dsn~~=PG:dbname=pgis_nc format=PostgreSQL olayer=urbanarea --o		{{cmd\|v.out.ogr}} input=u input=PG:dbname=pgis_nc format=PostgreSQL olayer=urbanarea --o

	* PostGIS input (geometry + attributes) - OGR data driver		* PostGIS input (geometry + attributes) - OGR data driver
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	{{cmd\|g.mapset}} pg_ogr		{{cmd\|g.mapset}} pg_ogr
	export GRASS_VECTOR_OGR=1		export GRASS_VECTOR_OGR=1
	{{cmd\|v.external}} ~~dsn~~=PG:dbname=pgis_nc layer=bridges output=b --o		{{cmd\|v.external}} input=PG:dbname=pgis_nc layer=bridges output=b --o
	{{cmd\|v.external}} ~~dsn~~=PG:dbname=pgis_nc layer=urbanarea output=u --o		{{cmd\|v.external}} input=PG:dbname=pgis_nc layer=urbanarea output=u --o

	* PostGIS input (geometry + attributes) - GRASS-PostGIS data driver		* PostGIS input (geometry + attributes) - GRASS-PostGIS data driver

	{{cmd\|g.mapset}} pg		{{cmd\|g.mapset}} pg
	{{cmd\|v.external}} ~~dsn~~=PG:dbname=pgis_nc layer=bridges output=b --o		{{cmd\|v.external}} input=PG:dbname=pgis_nc layer=bridges output=b --o
	{{cmd\|v.external}} ~~dsn~~=PG:dbname=pgis_nc layer=urbanarea output=u --o		{{cmd\|v.external}} input=PG:dbname=pgis_nc layer=urbanarea output=u --o

	Writing output directly using OGR library (mapset 'pg_ogr'):		Writing output directly using OGR library (mapset 'pg_ogr'):

Neteler: remove hardcoded version=70 manual links, no longer needed

2017-01-17T17:05:49Z

remove hardcoded version=70 manual links, no longer needed

Show changes

Neteler: /* Raster data processing workflow with keeping data external */

2015-10-10T21:07:53Z

Raster data processing workflow with keeping data external

← Older revision		Revision as of 21:07, 10 October 2015
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	{{cmd\|r.external\|version=70}} input=ncrast/urban.tif output=urban		{{cmd\|r.external\|version=70}} input=ncrast/urban.tif output=urban

	== Raster data processing workflow ~~with~~ keeping data external ==		=== Raster data processing workflow when keeping data external ===

	External raster maps can directly be linked into GRASS with {{cmd\|r.external}} which saves time and disk space. Additionally, there is no more a need to store results in the internal GRASS format - with {{cmd\|r.external.out}} the resulting maps are directly written to a GDAL supported format.		External raster maps can directly be linked into GRASS with {{cmd\|r.external}} which saves time and disk space. Additionally, there is no more a need to store results in the internal GRASS format - with {{cmd\|r.external.out}} the resulting maps are directly written to a GDAL supported format.

Neteler: +Raster data processing workflow with keeping data external

2015-10-10T21:07:27Z

+Raster data processing workflow with keeping data external

← Older revision		Revision as of 21:07, 10 October 2015
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	{{cmd\|r.external\|version=70}} input=ncrast/urban.tif output=urban		{{cmd\|r.external\|version=70}} input=ncrast/urban.tif output=urban

			== Raster data processing workflow with keeping data external ==

			External raster maps can directly be linked into GRASS with {{cmd\|r.external}} which saves time and disk space. Additionally, there is no more a need to store results in the internal GRASS format - with {{cmd\|r.external.out}} the resulting maps are directly written to a GDAL supported format.

			'''Preparations'''

			GRASS can be used in an automated way by just defining a set of variables. See here for [[GRASS_and_Shell#Setting_the_variables\|GRASS and Shell]] settings and [[GRASS_and_Python#Creating_Python_scripts_that_call_GRASS_functionality_from_outside\|GRASS and Python]].

			'''Data flow example'''

			The script content could be looking like this:

			<source lang="bash">
			# register (rather than import) a GeoTIFF file in GRASS GIS:
			r.external input=terra_lst1km20030314.LST_Day.tif output=modis_celsius

			# define output directory for files resulting from subsequent calculations:
			r.external.out directory=$HOME/gisoutput/ format="GTiff"

			# perform calculations (here: extract pixels > 20 deg C)
			# store output directly as GeoTIFF file, hence add the .tif extension:
			r.mapcalc "warm.tif = if(modis_celsius > 20.0, modis_celsius, null() )"

			# cease GDAL output connection and turn back to write standard GRASS raster files:
			r.external.out -r

			# use the result elsewhere
			qgis $HOME/gisoutput/warm.tif
			</source>

	== Vector data ==		== Vector data ==

⚠️Landa: /* Using wxGUI */

2012-11-29T13:07:42Z

Using wxGUI

← Older revision		Revision as of 13:07, 29 November 2012
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	[[Image:wxgui-v.external.png\|center\|thumb\|400px\|wxGUI {{cmd\|v.external\|version=70}} dialog]]		[[Image:wxgui-v.external.png\|center\|thumb\|400px\|wxGUI {{cmd\|v.external\|version=70}} dialog]]
	[[Image:wxgui-v.external.out.png\|center\|thumb\|400px\|wxGUI {{cmd\|v.external.out\|version=70}} dialog]]		[[Image:wxgui-v.external.out.png\|center\|thumb\|400px\|wxGUI {{cmd\|v.external.out\|version=70}} dialog]]

			== See also ==

			* [[PostGIS]]
			* [[PostGIS Topology]]

	[[Category:Vector]]		[[Category:Vector]]
	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:GRASS 7]]		[[Category:GRASS 7]]

⚠️Landa at 15:23, 27 November 2012

2012-11-27T15:23:34Z

← Older revision		Revision as of 15:23, 27 November 2012
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	[[Image:wxgui-link-menu.png\|center\|frame\|Link external data - Layer Manager menu]]		[[Image:wxgui-link-menu.png\|center\|frame\|Link external data - Layer Manager menu]]

	~~[[Category:GRASS 7]]~~

	or from ''toolbar'' in Layer Manager.		or from ''toolbar'' in Layer Manager.
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	[[Image:wxgui-v.external.png\|center\|thumb\|400px\|wxGUI {{cmd\|v.external\|version=70}} dialog]]		[[Image:wxgui-v.external.png\|center\|thumb\|400px\|wxGUI {{cmd\|v.external\|version=70}} dialog]]
	[[Image:wxgui-v.external.out.png\|center\|thumb\|400px\|wxGUI {{cmd\|v.external.out\|version=70}} dialog]]		[[Image:wxgui-v.external.out.png\|center\|thumb\|400px\|wxGUI {{cmd\|v.external.out\|version=70}} dialog]]

			[[Category:Vector]]
			[[Category:FAQ]]
			[[Category:GRASS 7]]

⚠️Landa at 15:22, 27 November 2012

2012-11-27T15:22:10Z

← Older revision		Revision as of 15:22, 27 November 2012
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	This page ~~is dedicated~~ to ~~support for~~ external data in GRASS 7. See also [[PostGIS]] and [[PostGIS Topology]].		This page explains how to effectively work with external raster and vector data in GRASS 7. See also [[PostGIS]] and [[PostGIS Topology]].
	__TOC__		__TOC__
	== Raster data ==		== Raster data ==