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 <[email protected]> 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 [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list [email protected] https://stat.ethz.ch/mailman/listinfo/r-sig-geo [[alternative HTML version deleted]]
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