[R-sig-Geo] [STATSGRASS] v.stats.rast for category raster or vector cross statistics

[Roger Bivand]

On Mon, 22 Oct 2007, Matthew Perry wrote:

> Agustin,
>
>
> I would suggest taking a look at starspan
> (http://starspan.casil.ucdavis.edu/). It specializes in
> vector-on-raster analyses and has a --count-by-class flag for
> categorical rasters. I wrote a bit more about it at
> http://www.perrygeo.net/wordpress/?p=30 .
>
> - matt
> On 10/22/07, Agustin Lobo <Agustin.Lobo at ija.csic.es> wrote:
>> Dear lists,
>>
>> Given Av (vector of polygons) and Br (raster of a categorical variable,
>> i.e. a classification or a soil map) I want to calculate
>> for each polygon in Av, the surface of each category from Br.
>>
>> v.stats.rast almost does it, but calculates lumped stats for each
>> polygon (i.e, assumes that Br is a continuous variable).
>>
>
>> Alternatively, I could have Br as another vector Bv, but don't find
>> the way of calculating cross stats as r.stats -a in=Ar,Br would do for
>> raster layers.
>>
>> Converting Av into raster Ar is inconvenient, as the polygons are few
>> and small and would have to use a very samll cell size (Br is large)
>>
>> Any easier way through R?

StarSpan is a good suggestion for heavy lifting. Within R, you could look 
at the overlay methods in sp to create a vector for polygon membership of 
raster size, then write a tapply function to accumulate tables with zero 
counts on categories by the polygon index.

Roger

>>
>> --
>> Dr. Agustin Lobo
>> Institut de Ciencies de la Terra "Jaume Almera" (CSIC)
>> LLuis Sole Sabaris s/n
>> 08028 Barcelona
>> Spain
>> Tel. 34 934095410
>> Fax. 34 934110012
>> email: Agustin.Lobo at ija.csic.es
>> http://www.ija.csic.es/gt/obster
>>
>> _______________________________________________
>> statsgrass mailing list
>> statsgrass at grass.itc.it
>> http://grass.itc.it/mailman/listinfo/statsgrass
>>
>
>
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no