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George Huxtable wrote:
>
> If a POL function is used to provide an angle output, as the A of a (R,A)
> pair, is the resulting R of any value, or must it be discarded? That's a
> similar question to what Bill has been asking.
>
> Can that vector method also give the initial great-circle course, leaving A
> towards B? If so, do any mods need to be made to conform with common
> navigator's notations (LHA positive westwards, azimuth clockwise from
> North)?

Your first question is not one I can answer off the top of my head, but
the second is easy. Yes, there is a vector formulation for the great
circle course. This one is in Fortran, and is actually for computing
position angle on the celestial sphere. But it should work for azimuth
as well. I say "should" because I have never tried the Fortran routine:

http://www.iau-sofa.rl.ac.uk/2005_0901/sofa/pap.for

It's part of the IAU SOFA collection of positional astronomy routines:

http://www.iau-sofa.rl.ac.uk/

By the way, I have the full set of SOFA and JPL DE/LE ephemeris routines
combined into a single Windows DLL. A C language program to demonstrate
the DLL isn't done yet. When it is, I'll give the whole package to
anyone who's interested.

   

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