[R-sig-eco] [R] rpart with circular data?

[Dean Urban]

hi all,

if it's potential radiation load that has you interested in aspect, you 
might look at this paper:

Pierce, K.B., T.R. Lookingbill, and D.L. Urban. 2005. A simple method 
for estimating potential relative radiation for landscape-scale 
vegatation analysis. Landscape Ecology 20:137-147.

it reviews the ways that folks have modeled this.

dlu

Abraham de Alba A. wrote:
> 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 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.
> 
> 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
>>
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> 
> 
> 
> 
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-- 
Dean Urban
The Nicholas School
Duke University
Durham, NC 27708 USA