On Fri, Aug 31, 2012 at 11:58 AM, Rowlingson, Barry
<b.rowling...@lancaster.ac.uk> wrote:
> If I didn't have to be on a train in three hours I'd code this up...
Oh who am I kidding:
buildTopo <- function(lines){
require(rgeos)
require(igraph)
g = gIntersection(lines,lines)
edges =
do.call(rbind,lapply(g@lines[[1]]@Lines,function(ls){as.vector(t(ls@coords))}))
lengths = sqrt((edges[,1]-edges[,3])^2+(edges[,2]-edges[,4])^2)
froms = paste(edges[,1],edges[,2])
tos = paste(edges[,3],edges[,4])
graph = graph.edgelist(cbind(froms,tos),directed=FALSE)
E(graph)$weight=lengths
return(graph)
}
> m = readOGR(".","Line")
> gg = buildTopo(m)
compute shortest distance between two vertices (note the -1 is because
I'm still on old igraph with 0-indexing):
> E(gg)[get.shortest.paths(gg,V(gg)[1],V(gg)[14])[[1]]-1]
Edge sequence:
[0] 0.81711193 47.57711634 -- -0.28546154 48.4287593
[1] 2.2151139 46.49728033 -- 0.81711193 47.57711634
[9] 1.57160852 45.36348513 -- 2.2151139 46.49728033
[10] 1.39973834 45.06066625 -- 1.57160852 45.36348513
[11] 1.29755246 44.88062446 -- 1.39973834 45.06066625
[12] 0.91544563 43.67971729 -- 1.29755246 44.88062446
[13] 0.88815229 43.43407719 -- 0.91544563 43.67971729
I think this could be improved by adding the coordinates to the nodes.
But anyway, 90% done.
Barry
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