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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@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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