[GRASS-user] computation in a location based on infos from another location

[Achim Kisseler]

Hi,

why dont you import one map from one location to another? Some
information will be lost, that would be the same like r.resamp.stats.

http://grass.itc.it/grass64/manuals/html64_user/r.proj.html

Achim

Patrice Dumas schrieb:
> Hello,
> 
> I have 2 locations, one with a lambert projection with a 1 km grid
> (comes from hydro1k), covering africa, and the other with a longitude latitude
> projection with a 0.5 decimal degrees grid (covering the world). I have a 
> raster map on the lambert location that has values of 1 for a given area and 
> 0 (or null) otherwise (corresponds with upstream basins) and I would like to 
> compute the corresponding area covered on the lonlat grid. This would lead 
> to a value for each cell in the lonlat grid corresponding with the fraction
> of the grid cell covered by 1 in the lambert map. So, for example, if the 
> cell is completly in the area in the lambert map, the value in the lonlat map
> should be 1, and if half of the area of the cell from the lonlat map
> is covered by ones in the lambert map, the value in the lonlat map should
> be 0.5.
> 
> If the two maps were in the same location, I could set the region
> to be the one of the lonlat map, and do
> 
> r.resamp.stats -w input=lambert_map output=fraction_covered
> 
> But r.resamp.stats doesn't work with maps from different locations.
> And it seems to me that r.proj forgets the information about the 
> initial grid although in this case it should be kept.
> 
> I have read the manual pages and the wiki but couldn't find anything
> answering my question, except that it seems to be something uneasy to 
> do in grass, since operations on different locations cannot be done in order
> to avoid losses of accuracy:
> http://grass.osgeo.org/wiki/Location_and_Mapsets
> 
> I may be wrong, but it seems to me that this kind of use of ratios to 
> interpolate from a grid to another would be something that is done
> regularly, and I guess that other kind of computations requiring
> that geographic informations are not lost for each map would also
> be useful.
> 
> --
> Pat
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