pseudo satellite positioning system

[David Wheatley]

Ronald Wiemer wrote:

> I am looking for a device that can be used as a real world digitizer.
> It needs a higher accuracy then a GPS can offer, but less than a
> total station. I am thinking of a system that consists of  3
> transmitters and a receiver, connected to a pen computer. It has to
> operate on an area of approx. 200 x 200 m. ( an archaeological site).

I once saw a unit called a '3-space tracker' which was used on at Sutton
Hoo to plan the 'sand shaddow' burials there. I think it is made by
Hewlett Packard but it was *very* expensive. It consisted of a base unit
and a kind of 3-d puck which moved about in the electromagnetic field of
the base unit. I don't think that it had a range as great as 100s of
metres, but accuracy was of the order of milimetres (I think Paul Reilly
did the work, and it may be published in CAA).

Another alternative is code-phase GPS, which is far more accurate than
any of the normal carrier-phase units - sub-centimetre I think. But this
is also big bucks. It's sometimes called 'survey grade GPS' and I think
Trimble make some equipment.

David Wheatley
Department of Archaeology
University of Southampton