Dear Alastair,

Example 1 in the gdistance vignette shows how to implement an asymmetric transition function using slopes.

You would need to define the function yourself, based on the literature on the physics of dispersal in complex topography or whatever is known about the dispersal of the species you are looking at.

Best,


Jacob.



On Thursday, 6 March 2014, 6:19, Alastair Potts <potts.a@gmail.com> wrote:
 
Hi all,

I have a plant species with a tumbling flower head - i.e. it gets blown
through the landscape by the wind.

I am very interested to see potential pathways that seeds could travel
between drainage basins, thus requiring the tumblers to traverse
watersheds. This would thus necessitate that the tumblers travel along the
flattest slopes possible. Distance isn't too much of a problem, but slope
is!

I have been familiarizing myself with the gdistance library and I think I
have understood it all, except the crucial transition function formula to
let increasing degrees of slopes heading upwards result in decreasing
conductivity and vice versa.

I've spent the last two days pondering this. Please could someone put me
out of my misery and help me: what would this transformation function look
like?

I have been alternating between operating on a DEM and a slope raster
generated from this DEM, but still not sure which I should use as I can't
figure out the function.

Any help would be very much appreciated.

Cheers,
Alastair

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