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    Re: Gnomonic Charts - Usable Zones
    From: Stan K
    Date: 2018 Jan 19, 11:24 -0500

    For great circle sailing, Celestial Tools will calculate:
    1) the initial course and distance given the departure and destination latitudes and longitudes
    2) the destination latitude and longitude given the departure latitude and longitude, the initial (true) course, and the distance
    3) the points in the great circle route at longitudes evenly divisible by 5º (a Power Squadrons standard, based on the main longitude lines on the gnomonic chart used), and the rhumb line course and distance between those points.

    A couple of examples are attached.


    -----Original Message-----
    From: Bob Goethe <NoReply_Goethe@fer3.com>
    To: slk1000 <slk1000@aol.com>
    Sent: Fri, Jan 19, 2018 2:45 am
    Subject: [NavList] Re: Gnomonic Charts - Usable Zones

    Thank you for this, Frank.
    Let me post a followup question not just to Frank but to whoever would like to respond:  I can use the Bygrave equations to calculate my initial great circle course and the distance from my current location to my destination.
    Is there another equation (or set of equations) that will let me say, "If I start from a certain latitude and longitude, and travel 200 nm on a course of θ°, what will be my latitude and longitude at the end of my journey?"  In a sense, I think my question is "Can I plan ahead my waypoints for a great circle route WITHOUT using a gnomonic chart?"
    If a mathematical solution to this is straightforward, that would be great. 
    If a table-driven approach is easier, I own a Volume 2 of Bowditch (1975 edition), as well as - of course - a downloaded Bowditch 2017.  If there is a table in one or both of these editions of Bowditch that will answer my question, I lack the skill to recognize that table for what it is.
    Thank you all for your assistance to me.



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