[R-sig-Geo] gdistance resistanceDistance error
karljarvis
karljarvis at gmail.com
Fri May 11 01:16:54 CEST 2012
Hi all,
As long as you're on the subject of the resistanceDistance function, I hope
you don't mind a different question. In a homogeneous landscape, shouldn't
equidistant points have the same resistance values? There is no
directionality to this implementation of the circuitscape-type approach, so
in a symmetrical landscape the matrix should be symmetrical. Right?
m <- matrix(1,10,10)
r <- raster(m)
t <- transition(r, mean, 8)
tg <- geoCorrection(t,type="c",multpl=FALSE)
x <- c(0.25,0.25,0.75,0.75)
y <- c(0.25,0.75,0.25,0.75)
xy <- cbind(x,y)
(rd <- resistanceDistance(tg,xy))
output:
1 2 3
2 373.2277
3 243.5229 266.6885
4 396.3933 322.7020 452.4068
The distance between each of these pairs of points are the same: (1,2),
(1,3), (2,4), (3,4), and these two are the same distance from each other:
(1,4), and (2,3). So since all else is equal, why are their resistances
different?
Thanks,
Karl
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