[GRASS-user] GRASS & earth curvature correction (viewsheds, LOS)

[Hamish]

> > > As far as I can tell, this is a mis-understanding. The
> > > value "0.325" applies to radio waves. Visible light is
> > > very close to 1:7.
> > 
> > What if I am interested in radio waves, not visible light,
> > e.g. for antenna relay positions? IMHO, that refraction
> > coefficient should not be hard-coded.
> 
> Agreed. It's a settable value in r.ecurv.comp and should
> also be one in all GRASS modules that have refraction
> compensation.

ok good point, wavelength matters & VHF LOS propagation distance
is an important problem to model. r.viewshed now has a user
settable refection coefficient in the range 0.0-1.0.
coeff=0.0 is like no refraction, 1.0 totally cancels out
any curvature of the Earth.

btw 1/7 is not 0.13, it's ~0.143. (to be picky)


Hamish