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= Support Material =
= Support Material =
* Vector data: have enough vertices in your vector data: [[File:V proj result.png|300px|center|thumb|Results in EU LAEA (EPSG: 3035)]]
* Ready to use .PRJ files (in the usual WKT format) as used by recent versions of ESRI ArcView: [http://esri-germany.de/downloads/software/Koordinatensysteme.zip download]
* Ready to use .PRJ files (in the usual WKT format) as used by recent versions of ESRI ArcView: [http://esri-germany.de/downloads/software/Koordinatensysteme.zip download]


= Important: have enough vertices in your vector data =
= See also =


When reprojecting vector data, it is important to have enough vertices in the data.
View Map Projections
* http://map-projections.net/singleview.php
* [http://www.progonos.com/furuti/MapProj/Normal/TOC/cartTOC.html Cartographical Map Projections] by Carlos A. Furuti


Example: Box (polygon) created with {{cmd|v.in.region}}:
Lists
* [http://www.epsg-registry.org/ EPSG Dataset]
* [https://www.asprs.org/asprs-publications/grids-and-datums ASPRS Grids and Datum]
* [http://geotiff.maptools.org/proj_list/ Projections Transform List (PROJ4)]
* [http://www.mapref.org/ MapRef - The Collection of Map Projections and Reference Systems for Europe]
* [http://www.crs-geo.eu Information and Service System for European Coordinate Reference Systems - CRS]


g.region n=60 s=40 w=0 e=30 res=10 -p
Related to Germany:
v.in.region box_latlong_10deg
* http://support.esri-germany.de/files/support/KoordinatensystemeInDeutschland.pdf
* http://support.esri-germany.de/files/support/KoordinatensystemeNachbarnDeutschlands.pdf
* http://support.esri-germany.de/files/support/KoordinatensystemeWeltweit.pdf


[[Image:V proj input unsplit boundaries.png|300px|center|thumb|4 corner rectangle, LatLong (no further vertices)]]<br>
Related to Austria:
* [http://www.alectoria.at/content/view/17/1/ Projection parameters of Austria]


v.split -n box_latlong_10deg output=box_latlong_10deg_vertices_200km length=200 units=kilometers
== Google Map Projection ==


[[File:V proj input split boundaries.png|300px|center|thumb|Split rectangle, LatLong]]<br>
Also called "pseudo-mercator" - note that there are many issues with this projection! Handle with care.


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
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):
grass70 -c box_latlong_10deg_EU_LAEA.shp ~/grassdata/eulaea
v.proj box_latlong_10deg 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)]]<br>
= See also =
* In English:
** [http://www.epsg.org/Geodetic.html EPSG Geodetic Parameter Dataset]
** [http://www.asprs.org/resources/grids/ ASPRS Grids and Datum]
** [http://www.remotesensing.org/geotiff/proj_list/ Projections Transform List (PROJ4)]
** [http://www.mapref.org/ MapRef - The Collection of Map Projections and Reference Systems for Europe]
** [http://www.crs-geo.eu Information and Service System for European Coordinate Reference Systems - CRS]
*  In German language:
** http://support.esri-germany.de/files/support/KoordinatensystemeInDeutschland.pdf
** http://support.esri-germany.de/files/support/KoordinatensystemeNachbarnDeutschlands.pdf
** http://support.esri-germany.de/files/support/KoordinatensystemeWeltweit.pdf
** [http://www.alectoria.at/content/view/17/1/ Projection parameters of Austria]
== Google Map Projection ==
* http://www.sharpgis.net/2007/07/27/TheMicrosoftLiveMapsAndGoogleMapsProjection.aspx
* http://www.sharpgis.net/2007/07/27/TheMicrosoftLiveMapsAndGoogleMapsProjection.aspx
* http://cfis.savagexi.com/articles/2006/05/03/google-maps-deconstructed
* http://cfis.savagexi.com/articles/2006/05/03/google-maps-deconstructed


[[Category: FAQ]]
[[Category: FAQ]]

Latest revision as of 16:37, 30 December 2019

Projections and Datum Transformations

Brief introduction to projections and spatial transformations in GRASS

A GRASS location is referenced with a single projection and coordinate system (or unreferenced as XY location). When creating a new location from an existing raster or vector map using the tools available from the startup screen or the map import commands, projection and coordinate system are defined. To change the projection of maps, a new location has to be created and the desired maps have to be reprojected into it from the source location as explained below.

Read on in projectionintro...

Creation of a GRASS location

Support Material

  • Vector data: have enough vertices in your vector data:
    Results in EU LAEA (EPSG: 3035)
  • Ready to use .PRJ files (in the usual WKT format) as used by recent versions of ESRI ArcView: download

See also

View Map Projections

Lists

Related to Germany:

Related to Austria:

Google Map Projection

Also called "pseudo-mercator" - note that there are many issues with this projection! Handle with care.

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