I've yet to see many robust implementations of visibility analysis -I
used to use this as the case study for how to lie with GIS when I
lectured on the subject.
variability within the limits of precision of DEMS (or whatever else you
use to map the terrain) cause huge error margins in the computed
visibility. Any accuracy issues (actual errors outside the limits of
precision) are disastrous..
I saw one example using Monte Carlo techniques (to introduce repeated
random changes within the limits of precision) that concluded that the
actual viewshed cannot be measured to within about 50% of the real
value. I.e. if you think you have 100 ha of viewshed, it may be 50 or 200!
Still, it makes pretty pictures to please politicians I suppose, but
please be careful about implementing a poor aproach (i.e. if the inbuilt
tools created a min and max and average position for a line of sight,
this would promote better analysis, and make the tool more important. I
dont know how hard this is to achieve for an entire viewshed - suspect
the algorithms would be quite tricky, but for a single line of sight its
pretty simple.
Rob
Andrea Antonello wrote:
Hi developers,
is there some class that does line of sight (visibility analysis) taking
into consideration the earth curvature?
I think I saw something, but I can't find it any more.
Thanks,
Andrea
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