For aspect, vegetation ecologist usually use an angular transformation, don´t have the reference at hand but that's the road that Dean L. Urban used for his CART analysis of Sequoia Nat. Park
   
  

Bálint Czúcz <czucz@botanika.hu> wrote:
  Hi Rainer,

In a similar situation I used the two components of the normal vector
of the surface ("northing" & "easting"). I.e. for a horizontal plane
both are 0, for a vertical slope facing south northing=-1and
easting=0, etc. This descartian decomposition of the slope vector
avoids the problem of circularity present in the widespreadly used
polar (aspect, slope) decomposition, and thus seems to suit ecological
problems much better to me. However I have not looked into this much,
I am also very interested in the opinion of others.

Bálint


On Mon, May 12, 2008 at 11:35 AM, Rainer M Krug wrote:
> Hi
>
> I am planning to use a CART analysis with rpart() to analyse the
> impact of, among others, slope, altitude and aspect on mortality
> rates.
> My question is:
> Is there a p[roblem with using aspect as a predictor as it is circular?
> And if it is a problem (which I suspect), is there a transformation I
> could use to transform aspect?
>
> Thanks
>
> Rainer
>
> --
> Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
> Biology, UCT), Dipl. Phys. (Germany)
>
> Plant Conservation Unit
> Department of Botany
> University of Cape Town
> Rondebosch 7701
> South Africa
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Bálint Czúcz
Institute of Ecology and Botany of the Hungarian Academy of Sciences
H-2163 Vácrátót, Alkotmány u. 2-4. HUNGARY
Tel: +36 28 360122/157 +36 70 7034692

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