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    Re: gyroscopic compasses
    From: George Huxtable
    Date: 2007 Jun 23, 14:25 +0100

    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?
    
    George.
    
    contact George Huxtable at george---.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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