[Proj] website cartographic executables---Inv_Fwd

[Oscar van Vlijmen]

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

> Just an added note here: check the NGS site for full precision online
> geodesic computations:
> http://www.ngs.noaa.gov/TOOLS/Inv_Fwd/Inv_Fwd.html

Highly recommendable!
I use it since version 1. Here & there are still version 1 implementations
alive, but I strongly recommend to update to the latest version. Better
accuracy, especially around antipodal point.
One pitfall silly ol' me fell into, long ago: I thought the 3d version gave
the true arc length going from height 1 in point 1 to height 2 in point 2.
But the functions only work with ellipsoidal distances as if the heights
were zero!
The accuracy is according to Vincenty only 0.01 mm for meridional arcs, not
full machine precision.