Map Reprojection - Revision history

Pvanbosgeo: correct typo

2024-08-25T09:02:45Z

correct typo

← Older revision		Revision as of 09:02, 25 August 2024
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	'''Question''': How to change map/image projections, datums, etc in GRASS GIS?		'''Question''': How to change map/image projections, datums, etc in GRASS GIS?

	'''Answer''': For quality reasons, GRASS GIS handles '''one projection per location'''. You can reproject ~~bewteen~~ locations as well as reproject during data import if needed.		'''Answer''': For quality reasons, GRASS GIS handles '''one projection per location'''. You can reproject between locations as well as reproject during data import if needed.

Neteler: + CRS Explorer - PROJ codes

2023-04-24T07:36:32Z

+ CRS Explorer - PROJ codes

← Older revision		Revision as of 07:36, 24 April 2023
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	Other publications and sites:		Other publications and sites:
			* [https://crs-explorer.proj.org CRS Explorer - PROJ codes]
	* [http://projections.mgis.psu.edu Interactive Album of Map Projections 2.0]		* [http://projections.mgis.psu.edu Interactive Album of Map Projections 2.0]
	* [https://map-projections.net/singleview.php View Map Projections]		* Compare Map Projections: [https://map-projections.net/singleview.php View Map Projections]

	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:Raster]]		[[Category:Raster]]
	[[Category:Vector]]		[[Category:Vector]]

Neteler: increase screenshot size

2021-06-20T16:00:37Z

increase screenshot size

← Older revision		Revision as of 16:00, 20 June 2021
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	v.in.region box_latlong_10deg		v.in.region box_latlong_10deg

	[[Image:V proj input unsplit boundaries.png\|~~300px~~\|center\|thumb\|4 corner rectangle, LatLong (no further vertices)]]<br>		[[Image:V proj input unsplit boundaries.png\|450px\|center\|thumb\|4 corner rectangle, LatLong (no further vertices)]]<br>

	Update 12/2014: vertex densification is now automatically done in {{cmd\|v.proj}} of GRASS GIS 7! Just use v.proj and it will be right.		Update 12/2014: vertex densification is now automatically done in {{cmd\|v.proj}} of GRASS GIS 7! Just use v.proj and it will be right.
	<strike>v.split -n box_latlong_10deg output=box_latlong_10deg_vertices_200km length=200 units=kilometers</strike>		<strike>v.split -n box_latlong_10deg output=box_latlong_10deg_vertices_200km length=200 units=kilometers</strike>

	[[File:V proj input split boundaries.png\|~~300px~~\|center\|thumb\|Split rectangle, LatLong]]<br>		[[File:V proj input split boundaries.png\|450px\|center\|thumb\|Split rectangle, LatLong]]<br>

	As obvious from the results, enough vertices must be present in the map to avoid (severe) distortion. Note that this applies likewise to "ogr2ogr" and QGIS:		As obvious from the results, enough vertices must be present in the map to avoid (severe) distortion. Note that this applies likewise to "ogr2ogr" and QGIS:
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	v.proj box_latlong_10deg_vertices_200km location=latlong_wgs84 mapset=neteler		v.proj box_latlong_10deg_vertices_200km location=latlong_wgs84 mapset=neteler

	[[File:V proj result.png\|~~300px~~\|center\|thumb\|Results in EU LAEA (EPSG: 3035)]]		[[File:V proj result.png\|450px\|center\|thumb\|Results in EU LAEA (EPSG: 3035)]]

	# Test in OGR/QGIS		# Test in OGR/QGIS

Neteler: Links updated

2019-12-30T15:18:03Z

Links updated

← Older revision		Revision as of 15:18, 30 December 2019
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	* [[Location and Mapsets]]		* [[Location and Mapsets]]
	* [[WxGUI]]		* [[WxGUI]]
			* [[Projection]]s

	Other publications and sites:		Other publications and sites:
	* Catalog of projections: http://proj4.org/projections
	* [http://projections.mgis.psu.edu Interactive Album of Map Projections 2.0]		* [http://projections.mgis.psu.edu Interactive Album of Map Projections 2.0]
	* [~~http~~://map-projections.net/singleview.php View Map Projections]		* [https://map-projections.net/singleview.php View Map Projections]

	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:Raster]]		[[Category:Raster]]
	[[Category:Vector]]		[[Category:Vector]]

Veroandreo: /* Reprojecting data in GRASS GIS */

2017-11-30T16:31:59Z

Reprojecting data in GRASS GIS

← Older revision		Revision as of 16:31, 30 November 2017
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	Variant 1:<br>		Variant 1:<br>
	# first create a location from the dataset itself (e.g. using the [[GRASS Location Wizard]]		# first create a location from the dataset itself (e.g. using the [[GRASS Location Wizard]])
	# second: use {{cmd\|r.import}} or {{cmd\|v.import}}		# second: use {{cmd\|r.import}} or {{cmd\|v.import}}

Neteler: View Map Projections

2016-09-12T12:03:32Z

View Map Projections

← Older revision		Revision as of 12:03, 12 September 2016
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	* Catalog of projections: http://proj4.org/projections		* Catalog of projections: http://proj4.org/projections
	* [http://projections.mgis.psu.edu Interactive Album of Map Projections 2.0]		* [http://projections.mgis.psu.edu Interactive Album of Map Projections 2.0]
			* [http://map-projections.net/singleview.php View Map Projections]

	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:Raster]]		[[Category:Raster]]
	[[Category:Vector]]		[[Category:Vector]]

Neteler: * Catalog of projections: http://proj4.org/projections

2016-09-02T13:11:01Z

* Catalog of projections: http://proj4.org/projections

← Older revision		Revision as of 13:11, 2 September 2016
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	'''Question''': How to change map/image projections, datums, etc in GRASS GIS?		'''Question''': How to change map/image projections, datums, etc in GRASS GIS?

	'''Answer''': For quality reasons, GRASS GIS handles '''one projection per location'''.		'''Answer''': For quality reasons, GRASS GIS handles '''one projection per location'''. You can reproject bewteen locations as well as reproject during data import if needed.


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	=== Reprojecting data in GRASS GIS ===		=== Reprojecting data in GRASS GIS ===

	# first create an location in the source projection/geodetic datum (using the [[GRASS Location Wizard]] d you can generate the location from the dataset itself)		Variant 1:<br>
			# first create a location from the dataset itself (e.g. using the [[GRASS Location Wizard]]
			# second: use {{cmd\|r.import}} or {{cmd\|v.import}}

			Ready.

			Variant 2:<br>
			# first create a location in the source projection/geodetic datum (using the [[GRASS Location Wizard]]; note that you can generate the location from the dataset itself)
	# [[Importing data\|import]] the map/image into the location,		# [[Importing data\|import]] the map/image into the location,
	# create a second destination location in the projection/geodetic datum you want to reproject the map/image into,		# create a second destination location in the projection/geodetic datum you want to reproject the map/image into,
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	Ready.		Ready.

			Variant 3:<br>
	Another (similar) strategy frequently needed when maps need to be imported using, e.g. {{cmd\|v.in.ogr}} or {{cmd\|r.in.gdal}}, is to tell these programs to create a new location (argument "location"). If the imported data contains proper <code>PROJ_INFO</code> files, they can be reprojected into the current mapset, using the the projection in the current location/mapset.		Another (similar) strategy frequently needed when maps need to be imported using, e.g. {{cmd\|v.in.ogr}} or {{cmd\|r.in.gdal}}, is to tell these programs to create a new location (argument "location"). If the imported data contains proper <code>PROJ_INFO</code> files, they can be reprojected into the current mapset, using the the projection in the current location/mapset.

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	=== Vector data: have enough vertices in your vector data ===		=== Vector data: have enough vertices in your vector data ===

	When reprojecting vector data, it is important to have enough vertices in the data.		When reprojecting vector data, it is important to have enough vertices in the data. Starting from GRASS GIS 7 the vertices are automatically densified.

	Example: Box (polygon) created with {{cmd\|v.in.region}}:		Example: Box (polygon) created with {{cmd\|v.in.region}}:
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	Other publications and sites:		Other publications and sites:
			* Catalog of projections: http://proj4.org/projections
	* [http://projections.mgis.psu.edu Interactive Album of Map Projections 2.0]		* [http://projections.mgis.psu.edu Interactive Album of Map Projections 2.0]

Neteler: +Interactive Album of Map Projections 2.0

2016-04-13T13:24:49Z

+Interactive Album of Map Projections 2.0

← Older revision		Revision as of 13:24, 13 April 2016
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	* [[Location and Mapsets]]		* [[Location and Mapsets]]
	* [[WxGUI]]		* [[WxGUI]]

			Other publications and sites:
			* [http://projections.mgis.psu.edu Interactive Album of Map Projections 2.0]

	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:Raster]]		[[Category:Raster]]
	[[Category:Vector]]		[[Category:Vector]]

Neteler: /* Vector data: have enough vertices in your vector data */

2016-02-07T22:16:05Z

Vector data: have enough vertices in your vector data

← Older revision		Revision as of 22:16, 7 February 2016
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	[[Image:V proj input unsplit boundaries.png\|300px\|center\|thumb\|4 corner rectangle, LatLong (no further vertices)]]<br>		[[Image:V proj input unsplit boundaries.png\|300px\|center\|thumb\|4 corner rectangle, LatLong (no further vertices)]]<br>

	Update 12/2014: vertex densification is now automatically done in v.proj of GRASS GIS 7! Just use v.proj and it will be right.		Update 12/2014: vertex densification is now automatically done in {{cmd\|v.proj}} of GRASS GIS 7! Just use v.proj and it will be right.
	<strike>v.split -n box_latlong_10deg output=box_latlong_10deg_vertices_200km length=200 units=kilometers</strike>		<strike>v.split -n box_latlong_10deg output=box_latlong_10deg_vertices_200km length=200 units=kilometers</strike>

Neteler: Update 12/2014: vertex densification is now automatically done in v.proj of GRASS GIS 7! Just use v.proj and it will be right

2014-12-02T22:46:41Z

Update 12/2014: vertex densification is now automatically done in v.proj of GRASS GIS 7! Just use v.proj and it will be right

← Older revision		Revision as of 22:46, 2 December 2014
Line 57:		Line 57:
	[[Image:V proj input unsplit boundaries.png\|300px\|center\|thumb\|4 corner rectangle, LatLong (no further vertices)]]<br>		[[Image:V proj input unsplit boundaries.png\|300px\|center\|thumb\|4 corner rectangle, LatLong (no further vertices)]]<br>

	v.split -n box_latlong_10deg output=box_latlong_10deg_vertices_200km length=200 units=kilometers		Update 12/2014: vertex densification is now automatically done in v.proj of GRASS GIS 7! Just use v.proj and it will be right.
			<strike>v.split -n box_latlong_10deg output=box_latlong_10deg_vertices_200km length=200 units=kilometers</strike>

	[[File:V proj input split boundaries.png\|300px\|center\|thumb\|Split rectangle, LatLong]]<br>		[[File:V proj input split boundaries.png\|300px\|center\|thumb\|Split rectangle, LatLong]]<br>
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	As obvious from the results, enough vertices must be present in the map to avoid (severe) distortion. Note that this applies likewise to "ogr2ogr" and QGIS:		As obvious from the results, enough vertices must be present in the map to avoid (severe) distortion. Note that this applies likewise to "ogr2ogr" and QGIS:

	# ~~Test in OGR/QGIS~~		# switch to a different location.
	v.~~out.ogr box_latlong_10deg dsn=box_latlong_10deg.shp~~
	~~ogr2ogr -t_srs epsg:3035 box_latlong_10deg_EU_LAEA.shp box_latlong_10deg.shp~~
	~~qgis box_latlong_10deg_EU_LAEA.shp~~
	~~# ... ops.~~

	# Properly reproject in GRASS GIS (when having used v.split):		# Properly reproject in GRASS GIS (when having used v.split):
	grass70 -c box_latlong_10deg_EU_LAEA.shp ~/grassdata/eulaea		grass70 -c box_latlong_10deg_EU_LAEA.shp ~/grassdata/eulaea
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	[[File:V proj result.png\|300px\|center\|thumb\|Results in EU LAEA (EPSG: 3035)]]		[[File:V proj result.png\|300px\|center\|thumb\|Results in EU LAEA (EPSG: 3035)]]

			# Test in OGR/QGIS
			v.out.ogr box_latlong_10deg dsn=box_latlong_10deg.shp
			ogr2ogr -t_srs epsg:3035 box_latlong_10deg_EU_LAEA.shp box_latlong_10deg.shp
			qgis box_latlong_10deg_EU_LAEA.shp
			# ... oops... (result not shown here).

	== See also ==		== See also ==