The simple picture of Earth is that of a sphere. However, as a result of its spinning it is somewhat flattened. distance calculations based on a spherical model can be as much as 0.5% off.
This page contains links to download a Windows program equivalent of Ed Williams's FAI distance calculator.
FAI distance calculator: by Ed Williams. Calculations use the Vicenty
Algorithm (Source: Direct and Inverse Solutions of Geodesics on the
Ellipsoid with Application of Nested Equations, Survey Review, XXII, 176
(1975)). See also the Aviation Formulary
(http://www.best.com/~williams/avform.htm), also by Ed Williams.
Ed Williams's code was adapted by Tony Lu to C++ classes that are used by the freeware GeoidTest program. The C++ classes are free to be used in non-commercial programs as long as Ed Williams 'sand Tony Lu's contributions are acknowledged.
Downloads updated on 29 March 2002.
Other Soaring Pilot Software programs:
GPS_LOG, Flight Display, ESRI shape, E00 and Digital Elevation Data files to GPS_LOG WinCE map converters, BLIPtoMAP overlay generator,and Magellan GPS to IGC track format converter.
For other things see the home page