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    Re: distance with atan2
    From: Paul Hirose
    Date: 2005 Nov 12, 10:41 -0800

    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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