|Re: HP48SX accuracy questioned.|
Message #4 Posted by hugh steers on 10 Sept 2009, 9:01 p.m.,
in response to message #3 by Eric Smith
the idea of a great circle is somewhat misleading in the context of earth navigation. use the spherical formulae for pure spheres, but for earth distances it's a bad idea.
for some time i've been using Meeus' formula. i put some code here, http://www.voidware.com/earthdist.htm
but recently, i became aware of a formula by Vincenty, http://en.wikipedia.org/wiki/Vincenty's_formulae. I read the paper and coded it up. it's a bit more complicated, but claims to be super accurate. However, i had problems with it not converging for points almost opposite the globe.
in any case, unless you really want to measure distances on WSG84, you're going to have a height difference involved which the, as presented, Vincenty formula doesn't deal with. so, im still happy to use the Meeus approximation for real use.
However, at some point im going to have to try to get something that takes height into account too.