[GRASS-user] least cost path between patches

[Patrick Giraudoux]

Dear listers,

I am trying to compute and represent the least cost paths between 
discrete patches (say distribution areas of a given species included in 
a landscape matrix). For training, I use a homogeneous cost surface (the 
landscape matrix, 'movecost') and a raster 'monkeygroup' of 12 discrete 
patches representing the species areas (1 for pixels on the patch, NULL 
out).

r.mapcalc "movecost=1.0"

I can easily get a distance map 'monkeycost' then,

r.cost input=movecost output=monkeycost start_rast=monkeygroup

Now, I would like to find out the shortest track(s) linking each patch 
to the others, and here I am stuck. r.drain supposes that one uses one 
geographical coordinate as a starting point. However I would like to 
link the nearest pixels belonging to each patch via a path that must go 
away from one patch, go up to the lowest local maximum and then go down 
to the next patch. This supposes that one can identify which pixels 
included are the nearest among two patches, and then compute the path... 
(hope it is understandable).

Is there any grass module doing the job, or has anybody an idea about a 
strategy to get the expected result?

Patrick