NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Distance on ellipsoid
From: Jim Easton
Date: 1996 Oct 30, 12:51 EST
From: Jim Easton
Date: 1996 Oct 30, 12:51 EST
It is not clear to me what all of the fuss is about regarding distance. I would hope that anyone trained in navigation could calculate great circle distances. I believe that there are numerous references to calculating distances on a sphere. I personally usually go back to the ITT Radio engineers handbook for their formulas. A more interesting issue is distance on a reference ellipsoid -- which is theoretically what one should really be doing. The precise formula involves elliptic integrals -- not just trigonometric functions. I have not kept up with the new editions, but Bowditch used to have formulas approximating the exact calculations. One needs to be a little cautious implementing these formulas on a computer since there may be ambiguities due to the multiple valuedness of inverse trig functions & some of the formulas blow up or become less accurate under certain input values. If anyone is interested, I will try to find the "real" formulas. Jim Jim Easton 4364 Bonita Rd., No. 166 Bonita, CA, 91902-1421 Tel: (619) 548-0138 FAX: (619) 470-8616
