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    Re: Bowditch
    From: Noel Casey
    Date: 2001 Jan 29, 5:59 AM

    This is a well known limitation of the arctangent(x,y) function as being
    ambiguous  for angles greater than 90 deg.
    The function Arctangent2(x,y) resolves the issue. I don't know if the VAX
    compiler handled that.
    In excel spreadsheet there is the atan and atan2 functions, with the atan2
    function being preferable in all cases.
    > -----Original Message-----
    > From- Roger M. Derby [SMTP:derbyrm@SEIDATA.COM]
    > Sent: Friday, January 26, 2001 7:45 PM
    > Subject:      Re: Bowditch [was Re: Hi (WAS: RE: ping)]
    > Just a word of caution that I'm sure is unnecessary.  When I was
    > programming
    > a VAX to do great-circle calculations (path length and departure) using
    > the
    > equations from Bowditch, I got some very strange results.  These turned
    > out
    > to be caused by the machine's math library making different assumptions
    > about quadrant than was used by Bowditch.  I finally made up a table of
    > entries for two points a few nm apart using paths that hit all four
    > quadrents and the four cardinal points and then checking against
    > "reasonable" answers.  Had to add several IF-THENs before Singapore was a
    > long way from the Lizard and in the correct direction.
    > Roger
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