[GRASS-user] Tobler's hiking function

[mlage at usal.es]

Hello
I am trying to express Tobler’s Hiking Function with r.mapcalc.
This is the expression that I’m trying to apply:

T = D / (6 exp (-3.5) * abs (S+0.05)))

T= time to cross the cell
D=resolution of the cell (in my case 25m)
S=slope in percent

I’m using it to calculate the time needed to cross a cell through the
relation between the traveling speed (in Km/hr) and the slope to generate
a friction surface.

After creating the slope map, I “translated” it like this:

r.mapcalc newmap=“(6 exp(-3.5*(abs(slopemap)+0.05)))/0.025”


slopemap it’s for S and 0.025 it’s for D.


What do you think about this? Am I "translating" it well?I would
appreciate you expert opinion.

Thank you!!!
Miguel Lage.