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

[Benjamin Ducke]

----- Original Message -----
> On Thu, May 26, 2011 at 12:26 PM, Benjamin Ducke
> <benjamin.ducke at oxfordarch.co.uk> wrote:
> >> Hm-hm. Citing from the website:
> >> "The problem is that the ratio of change due to air to curvature is
> >> not 1:7 (0.13), as the standard refraction coefficient suggests. It
> >> is 0.325.
> >
> > 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.

Ben

> >
> > I realize the whole discourse is somewhat "clouded". But I don't
> > have access to most of the relevant literature for the time
> > being, nor do I have the necessary scientific background
> 
> Me neither. But any correction should take into account that the
> observer is not necessarily a human without optical equipment
> (telescope etc), but can also be some technical device, e.g. a sender
> or receiver of whatever signals.
> 
> my .2c
> 
> Markus M
> 


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