[R-sig-Geo] gdistance: costDistance with barriers

[Stachelek, Joseph]

Hi Karl,

I think the underlying shortest.paths algorithm is wrapping around the x dimension of the raster. I was able to fix by remove vertices in the underlying adjacency matrix.

library(gdistance)
r <- raster(nrows=18, ncols=36)
r[] <- 1
t <- transition(r,function(x) 1/mean(x),4)
p <- cbind(seq(-120,120,by=40),rep(0,7))
costDistance(t,p)


#my code
source("gdistance_source/internal-functions.R")
x<-t
fromCoords<-toCoords<-p

fromCoords <- .coordsToMatrix(fromCoords)
toCoords <- .coordsToMatrix(toCoords)

fromCells <- cellFromXY(x, fromCoords)
toCells <- cellFromXY(x, toCoords)

##
costDist <- matrix(NA, nrow=length(fromCoords[,1]),ncol=length(toCoords[,1]))
rownames(costDist) <- rownames(fromCoords)
colnames(costDist) <- rownames(toCoords)
y <- transitionMatrix(x)
#if(isSymmetric(y)) {m <- "undirected"} else{m <- "directed"}
adjacencyGraph <- graph.adjacency(y, mode="directed")
E(adjacencyGraph)$weight <- 1/E(adjacencyGraph)$weight

uniqueFromCells <- unique(fromCells)
uniqueToCells <- unique(toCells)

extent(r)
removepnts <- cbind(rep(180,181),seq(-90,90,by=40))
removecells <- cellFromXY(x, removepnts)
adjacencyGraph<-delete.vertices(adjacencyGraph,removecells)

shortest.paths(adjacencyGraph, v=uniqueFromCells, to=uniqueToCells, mode="out", algorithm="dijkstra")








-----Original Message-----
From: R-sig-Geo [mailto:r-sig-geo-bounces at r-project.org] On Behalf Of karljarvis
Sent: Thursday, March 12, 2015 2:36 PM
To: r-sig-geo at r-project.org
Subject: [R-sig-Geo] gdistance: costDistance with barriers

Hi all,
I am seeing confusing behavior from the costDistance function in gdistance.
In general, when cost is constant, cost distance increases linearly with
actual distance. However, in this example, it is not doing that for the
longest few distances. Am I missing something?
Karl

r <- raster(nrows=18, ncols=36)
r[] <- 1
t <- transition(r,function(x) 1/mean(x),4)
p <- cbind(seq(-120,120,by=40),rep(0,7))
costDistance(t,p)

> costDistance(t,p)
   1  2  3  4  5  6
2  4
3  8  4
4 12  8  4
5 16 12  8  4
6 16 16 12  8  4
7 12 16 16 12  8  4



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