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

[Benjamin Ducke]

> > >
> > > 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)
> 

Yes, true. But ArcGIS uses 0.13 (for undisclosed reasons), and I 
originally wrote r.ecurv.comp to make it easy for ArcGIS users to 
switch to open source GIS and get comparable viewshed results. 
Of course, that doesn't mean r.viewshed has to do the same.

I have attached a version of r.ecurv.comp that behaves exactly
as you describe above. This way, users of current r.los and r.cva
can get the same corrected results.

Ben

> 
> Hamish



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