[R] calculate area of outer polygon

[Tord Snäll]

Dear all,
Does anyone know of a function that calculates the area of the outer 
polygon constructed from a data frame with co-ordinates? For example,
library(splancs)
test = rbind(c(0,0), c(10,0),c(10,10),c(0,20))
plot(test)
areapl(test)
[1] 150
This is OK, but I want the same area to be returned (150) when adding 
yet another co-ordinate in the middle of the polygon:
test = rbind(c(0,0), c(10,0),c(10,10),c(0,20),c(5,5))
plot(test)
areapl(test)
[1] 100

I have also tested area.owin() in library(spatstat) but the co-ordinates 
of the outer polygon is one of the arguments.


Thanks!

Tord

-- 

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Tord Snäll
Department of Conservation Biology
Swedish University of Agricultural Sciences (SLU)
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E-mail: tord.snall at nvb.slu.se
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