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    Re: Intermediate points in great circle courses
    From: Bill Murdoch
    Date: 1999 Jul 25, 8:20 PM

    In a message dated 7/25/99 1:33:54 PM EST, lu.abel{at}ATT.NET writes:
    > I told him that one would plot several intermediate points of the course on
    >  a Mercator chart and then steer the rhumb-line courses between them.  Then
    >  I realized I didn't know how to find intermediate points
    Lou, I think you have a copy of the text that goes with my TI-81
    astronavigation program.  In the code on page 144 is a formula for
    calculating the latitude for any point along a great circle course given the
    longitude of the point.  The formula would make it easy to prepare a table of
    lat/long points along a great circle course.
    C is the inital great circle course.
    dLo is the difference in longitude from the inital point to the point for
    which you are trying to determine the latitude.
    lat is the latitude of the initial point.
    lat2 is the latitude of the desired point.
    lat2 = tan-1((cos C * sin dLo / sin C + sin lat cos dLo) / cos lat)
    Bill Murdoch

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