r.roughness.vector: bug in rescale formula

[sbl]

There is a little bug in the formula that produces the "Fischers K" output (line 317). "- 1" should not be in there.

[hellik]

Replying to sbl:

There is a little bug in the formula that produces the "Fischers K" output (line 317). "- 1" should not be in there.

It's a port of g6 addon: https://grass.osgeo.org/grass64/manuals/addons/r.roughness.window.vector.html

Could you have a look how the calculation is there?

[sbl]

Yes, same issue there. For what I can see, line 265 in ​https://trac.osgeo.org/grass/browser/grass-addons/grass6/raster/r.roughness/r.roughness.window.vector.sh should be changed equally like this:

- r.mapcalc $FISHER = "($window * $window - $STRENGTH) / ($window * $window - 1)"
+ r.mapcalc $FISHER = "($window * $window - $STRENGTH) / ($window * $window)"

Result should be scaled from 0 to 1. Thus formula should be:

V' = (max(V[i-j]) - V) / max(V[i-j]

[hellik]

Replying to sbl:

Yes, same issue there. For what I can see, line 265 in ​https://trac.osgeo.org/grass/browser/grass-addons/grass6/raster/r.roughness/r.roughness.window.vector.sh should be changed equally like this:

- r.mapcalc $FISHER = "($window * $window - $STRENGTH) / ($window * $window - 1)"
+ r.mapcalc $FISHER = "($window * $window - $STRENGTH) / ($window * $window)"

Result should be scaled from 0 to 1. Thus formula should be:

V' = (max(V[i-j]) - V) / max(V[i-j]

Could you ping Carlos, the author of both addons, regarding this issue?

[guano]

Hi there, sorry for the late reply.

I went looking in the paper by Hobson (1972), and the original formula for Fischer K is: (N-1)/(N-R), but in the module (and in my paper) I used the *inverse* of it (so smooth areas would end up with a low value). Inverting the formula gives (N-R)/(N-1).

[neteler]

Ticket retargeted after milestone closed

[martinl]

Ticket retargeted after milestone closed

[neteler]

@guano: what's to be done here?