[Proj] website cartographic executables---Inv_Fwd

Oscar van Vlijmen ovv at hetnet.nl
Tue Dec 20 15:06:54 EST 2005

> From: "Gerald I. Evenden" <gerald.evenden-verizon.net>

>>> geodesic computations:
>>> http://www.ngs.noaa.gov/TOOLS/Inv_Fwd/Inv_Fwd.html

> What bothers me is I cannot conceptualize the 3D version.  What does the
> geodesic look like as it changes elevation?
Now don't let it keep you awake, since invers3d.for doesn't compute it
anyway. It would have been nice though to get a geodesic-like arc along an
ellipsoid that inflates or deflates while going from a point at height 1 to
another at height 2. I cannot imagine how I could fly such a route reliably
and it's a bit difficult to find a terrain that follows such a height
development, but dreaming doesn't hurt, innit?

> I can't help of thinking as the problem as line-of-sight.  That is, when I
> look at Mt. Everest from a plain 30 miles away I feel the problem is a
> matter of a simple xzy hypotenuse problem.
invers3d.for does compute that. It does chord distances, zenith distances,
north-east-up differences, that sort of things. And of course the distance
along the geodesic with height difference zero.

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