Hi Martin and Stefan, I understand, if we do not use the -a flag, we can not ensure that the resolution is the set.
What if there is another option, "align=", as Stefan suggested, which allows to choose a raster from the canvas? This would ensure that the region would be aligned with a selected raster? Thank you very much! Pedro 2016-03-12 10:44 GMT+00:00 Blumentrath, Stefan <[email protected]>: > > ________________________________________ > Von: Qgis-developer [[email protected]] im Auftrag > von gene [[email protected]] > Gesendet: Samstag, 12. März 2016 10:46 > An: [email protected] > Betreff: Re: [Qgis-developer] Problem with GRASS Region Extent and Region > Cellsize on Processing > > To keep the raster resolution. > > In the book "OPEN SOURCE GIS A GRASS GIS Approach Third Edition", p.57 > > "It may happen, that region boundaries lead to a modified, non-integer > raster resolution. If this is not desired, the -a flag can be used to align > the region to resolution. It adjusts all four boundaries to be even > multiples of the resolution by slightly enlarging the current region. To > see > the effect, compare: > g.region res=15 -dp > g.region res=15 -adp" > > Look also: > > - suggestion for g.region -a > < > http://osgeo-org.1560.x6.nabble.com/suggestion-for-g-region-a-td4014517.html > > > (Michael Barton) > > "Currently, if you use the -a flag with g.region it will align the region > exactly to match the resolution of a map (e.g. g.region -a rast=myrast will > set the region to exactly the resolution of myrast regardless of the > extents) or the resolution specified in the res or ewres/nwres fields (e.g. > g.region -a n=523 s=15 res=10 will adjust the extents a little to make sure > the resolution is exactly 10)" > > - or in proposal: make -a flag the default behaviour for g.region > <https://trac.osgeo.org/grass/ticket/1745> (Moritz Lennert) > > "In my experience, when working with raster, having a precise resolution is > the most important issue, while exact extension is less important. I often > use existing vector data or bounds coordinates to determine the extent, but > then have to use the -a flag to make sure that the desired resolution is > kept. > I would like to propose that in grass7, the behaviour is switched, i.e. to > make the -a flag (Align region to resolution) the default behaviour, and > "align to bounds" the option" > > > > I guess it depends a bit what the most suitable solution is... There is > also the "align" option which aligns the resolution to an input raster. > Personally, i only use tha a-flag only in combination with the res option... > Cheers, > Stefan > > > > > > -- > View this message in context: > http://osgeo-org.1560.x6.nabble.com/Problem-with-GRASS-Region-Extent-and-Region-Cellsize-on-Processing-tp5255693p5255960.html > Sent from the Quantum GIS - Developer mailing list archive at Nabble.com. > _______________________________________________ > Qgis-developer mailing list > [email protected] > List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer > Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer > _______________________________________________ > Qgis-developer mailing list > [email protected] > List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer > Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer >
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