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    Re: Mercator vs. Great Circle Charts
    From: Nigel Gardner
    Date: 2001 Aug 29, 3:15 PM

    In spite of the rather unfortunate initial exchanges, an interesting point
    is raised about what is meant by 'great circle charts'. Probably the most
    commonly used is Lambert's conformal, although not strictly a GC chart
    because of distortion away from the standard parallels is near enough for
    practical purposes, gnomonic projections (although correct) suffer from
    scale exaggeration away from the centre; esoteric ones such as the Mecca
    azimuthal or the Rugby diagram are precise but only from or to the one
    point. Interestingly when I was scratching a living navigating aircraft,
    for crossings between UK and Canada we calculated the latidude intercept
    for every 5deg of long. plotted these on a mercator and flew each leg as a
    rhumb line, any HF radio bearings that we got were plotted using the
    conversion angle. Other oceanic crossings tended to be at lowish latitudes
    so a mercator was good enough.
    A friend of mine was a master on super-tankers and required the mate of the
    watch to take a sun sight each day from the deck watch, arguing that GPS
    might get switched off or the nav equipment might suffer a major failure.

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