Two Antennas (was RE: "Blunkett u-turn on data privacy plans")

[Brian Gladman]

----- Original Message -----
From: "David Hansen" <davidh@spidacom.co.uk>
To: <ukcrypto@chiark.greenend.org.uk>
Sent: Tuesday, March 04, 2003 5:34 PM
Subject: Re: Two Antennas (was RE: "Blunkett u-turn on data privacy plans")


> On 4 Mar 2003 at 17:05, Brian Gladman wrote:
>
> > However these measurements would require a laboratory environment - as
> > you suggest, it does not seem likely that sub-cm resolution would be
> > possible in differential GPS measurements in a field environment.
>
> As the two antennas are likely to move by several mm relative to each
> other (due to wind, springy grass, backlash in the mountings and
> whatever) I would be inclined to say that such accuracy is
> impossible.

Under normal 'field' conditions I agree but are you saying that this level
of accuracy is impossible under any conditions?

If someone sets out to achieve mm accuracy using GPS signals they will have
to account for factors of the kind you mention.  This is what would be done
in laboratory conditions and explains why it is not uncommon to find that
laboratory measurements are orders of magnitude better than can be achieved
in more normal situations (which explains why things often go wrong when
people try to transfer laboratory results into the real world).

    Brian Gladman