[R-sig-Geo] Extracting minimum convex polygons of species distributions

[Mathieu Basille]

Dear Louise,

I think there is a couple of possibilities. You might be interested in 
clusthr, LoCoH.* and CharHull, also in the package adehabitatHR. Please 
check the vignette of the package, section 6:

vignette("adehabitatHR")

In addition, a new estimator could be useful to you as well: the PPA home 
range [1]. A R function based on ltraj objects (adehabitatLT) is available 
here: http://www.geog.uvic.ca/spar/PPAHomeRange/index.html

Hope this helps,
Mathieu.


[1] Jed A. Long and Trisalyn A. Nelson. 2012. Time geography and wildlife 
home range delineation.  The Journal of Wildlife Management, 76: 407–413. 
DOI: 10.1002/jwmg.259
http://onlinelibrary.wiley.com/doi/10.1002/jwmg.259/abstract



Le 15/03/2012 09:56, Louise Mair a écrit :
> Hello,
>
> I have a distribution dataset for species consisting of xy coordinates at
> the 1km resolution, with only presence data. So a simplified example of a
> species distribution might be:
>
> y<- rbind(as.integer(rnorm(100,50,20)), as.integer(rnorm(200,100,30)),
> as.integer(rnorm(100,180,15)))
> x<- rbind(as.integer(rnorm(200,50,20)), as.integer(rnorm(200,100,20)),
> as.integer(rnorm(100,200,15)))
> plot(y~x)
>
> I would like to create polygons for each species distribution, where if an
> island is present (as I have tried to show in the example), it would be a
> seperate polygon, and the jagged edges where species distributions meet
> coastlines etc are maintained. I have tried functions such as mcp in the
> package adehabitat, but this produces a very coarse polygon, which doesn't
> provide the detailed distribution edges that I need. Other functions I've
> tried require the data already to be in the format where the only xy
> coordinates present are the outline of the polygon.
>
> Can anyone please recommend a function I can use here, or suggest a way of
> extracting the outline points? I have tried this manually but cannot seem
> to write a code that will effectively take account of jagged edges and
> islands.
>
> Thanks very much for your help,
>
> Louise.
>
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>
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Mathieu Basille, Post-Doc

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Laboratoire d'Écologie Comportementale et de Conservation de la Faune
+ Centre d'Étude de la Forêt
Département de Biologie
Université Laval, Québec

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http://ase-research.org/basille

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``If you can't win by reason, go for volume.''
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