Region settings

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{{Content Tree|HEADER=QGIS Tutorial|NAME=QGIS tutorial}}
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#redirect[[GRASS region]]
 
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{{typed|text=g.region}} is a very important module because it manages the boundary definitions for
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geodata. Changing the settings means that you modify several parameters of a region:
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* geographical projection (e.g. UTM, Latitude-Longitude, Gauss-Krueger, etc),
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* geographical extension, i.e. the North/South/East/West limits of the area covered,
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* number of columns and number of rows for the data,
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* resolution, i.e. the extension divided by the number of rows (N-S resolution), respectively (E-W resolution).
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How  do we use it? One of several possibilies is to use the GRASS Shell.  Open the Toolbox click on {{mitem|text=Modules List → GRASS Shell}}.
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'''Synthax'''
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*{{typed|text=g.region [rast=name ] [vect=name ] [res=value ] -p -l}}
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'''Parameters'''
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*{{typed|text=[rast=name]}}= Set region to match this raster map
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*{{typed|text=[vect=name]}}= Set region to match this vector map
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*{{typed|text=[res=value]}}= Grid resolution 2D (both north-south and east-west)
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'''Flags'''
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*{{typed|text=-p}}= Print the current region
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*{{typed|text=-l}}= Print the current region in lat/long using the current ellipsoid/datum
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'''Why care about the region?'''
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The region defines the extension and geometric resolution (pixel size) of the data on
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which most GRASS (raster) commands work. If the region is set to a smaller extension
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than that of the map you are working on, display and results of raster processing
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commands will only show the portion of the map that is contained in that region.
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{{attention|text= In short, this means that whatever command you use in GRASS, it is always applied '''only to the data in the current region.'''}}
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[[category:Introduction to Quantum GIS]]
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Latest revision as of 17:22, 8 April 2011

  1. redirectGRASS region
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