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    Re: gyroscopic compasses
    From: Gary LaPook
    Date: 2007 Jun 23, 11:20 -0700

    Gary LaPook wrote:
    I don't know but I'm pretty happy with the performance of my Brunton
    pocket transit, and the're only a couple hundred bucks new and less on
    George Huxtable wrote:
    >Relating to Geoffrey Kolbe's suggestion that a laser "gyro" would make a
    >suitable handheld compass-
    >Nicolas de Hilster confirms my presumption that such systems remain
    >furiously complex and expensive.
    >But there's a more fundamental objection to their use as a simple handheld
    >compass, as I see it (on second thoughts).
    >What such instruments measure is the changes in orientation of three axes,
    >in absolute space. What a handheld compass is expected to provide is a
    >direction, toward true North, along the Earth's surface. But the plane of
    >the Earth's surface, at the position of the navigator, is changing, all the
    >time, for two reasons; because of the rotation of the Earth, and because of
    >the motion of the observer with respect to the surface of the Earth. So, any
    >such laser "gyro" would need to have some sort of knowledge of these
    >quantities. In a similar way, a ship's gyroscopic compass needs to have some
    >sensor of the local horizontal, and have correction factors applied which
    >allow for the vessel's motion.
    >I imagine that in the case of a laser "gyro", this information would be
    >provided by an interface with some form of GPS receiver, with a sensor of
    >the direction of gravity. But it takes us a long way from the simple
    >hand-held device of Geoffrey's concept. How does he propose it will work, in
    >more detail?
    >contact George Huxtable at george@huxtable.u-net.com
    >or at +44 1865 820222 (from UK, 01865 820222)
    >or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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