[Manifold-l] Visibility and earth curvature

[Neill Glover]

Greetings

Is there a factor that needs to be considered when creating a 
visibility area that takes into account the curvature of the earth.
In other words, say a visibility map was being generated up to a 
distance of 50km away from a structure, should there be any allowance 
for the earth curvature at that distance, as opposed to say 30 km away.

Thanks

Neill