Great circle formulae, True cource and actual heading

"Sims" wrote in
:

Hi,

I am trying to write a formula to compute flight headings.
If i use 2 lat/lon i can get a "true course" but due to magnetic
variations the true course is not really all that useful, (knowing
that my true course is 118deg will not tell me that i should fly 93
deg).

What i mean is if i go from A to B i can calculate the True course,
('tc') but my actual heading varies a lot depending on my position
along the course.

Is there a reliable formula to calculate my actual heading at a
certain point along the course?

Many thanks in advance.

Sims

At least in sci.geo.satellite-nav this sort of question about
formulae has been asked numerous times, including quite recent
threads, so a search via Google Groups would likely have already
found you your answer.

Take a look at Ed Williams page about Aviation Formulary:
http://williams.best.vwh.net/avform.htm

--
Dave Patton
Canadian Coordinator, the Degree Confluence Project
http://www.confluence.org dpatton at confluence dot org
My website: http://members.shaw.ca/davepatton/
Vancouver/Whistler - host of the 2010 Winter Olympics