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

[Hamish]

Markus Metz wrote:
> The original behaviour of r.viewshed was to distinguish
> between visible and invisible cells and cells for which
> visibility could not be determined because input elevation is
> NULL. r.los on the contrary sets both invisible cells and cells
> for which visibility could not be determined to NULL. I
> synchronized r.viewshed to r.los because r.los is in the main
> branches whereas r.viewshed is in addons.
> Distinguishing between invisible cells and cells for which
> visibility could not be determined might provide useful
> information, though.

well, AFAIR r.los uses NULL for that simply because that's what I
decided to do when I added NULL support to the module some years
ago.
So to distinguish between uncalculated (because beyond the
requested search radius?), and in-search-region but non-visible?

Well, it's not to me, but I guess potentially that's useful to
someone somewhere. I hate to needlessly lose information, but
in general I think NULL for non-visible is what you'd want the
output to show most of the time. So again I'm mildly in favour
of keeping out-of-sight = NULL, but not of too strong an opinion
about it.


Hamish