rpart with circular data?
On Mon, May 12, 2008 at 6:29 AM, B?lint Cz?cz <czucz at 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.
B?lint
On Mon, May 12, 2008 at 11:35 AM, Rainer M Krug <r.m.krug at gmail.com> 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 at 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