On Mon, May 12, 2008 at 6:29 AM, Bálint Czúcz <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> 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. >> > >
I would recommend going straight to the source-- modeling solar radiation. This gives a purely physical-based generalization of terrain-induced variation in microclimate. Keep an eye out for this paper, soon to be published in Soil. Sci, Soc, America: D.E. Beaudette, and A.T. O'Geen. Quantifying the Aspect Effect. Soil Sci. Soc. Am. J. March 3, 2008. (In Review) This paper uses a GRASS-based solution to the problem. Cheers Dylan ______________________________________________ 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.