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

[Markus Metz]

On Wed, May 25, 2011 at 12:34 PM, Hamish <hamish_b at yahoo.com> wrote:
> Benjamin wrote:

[...]
>>
>> I have not tested r.viewshed's curvature correction.
>> But if it uses the same method as r.los, then the
>> same observations apply.
>
> I'm not sure, but I suspect it might. MarkusM?

r.viewshed's correction for earth curvature is copied as is from (recent) r.los.

[...]
>
> [*] @MarkusM: re. changing out-of-view to NULL in r.viewshed, I
> now notice in the help page that NULL was previously reserved for
> NULLs in the original DEM. But in that case I suspect that
> everything in the shadow of the DEM's NULLs should also be NULL,
> as the visibility will be unknowable. I'm mildly in favour of
> keeping the code as-is, and changing the help page to match.
>
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.

Markus M