On Sun, 27 Jan 2008 17:05:39 +0100, Marc Heusser
d wrote in
:

In article ,
larry wrote:

Y'all give a cheap boat GPS WAY too much credit for position fixes!
It's only good to about 3 feet, on a sunny day, with no reflecting
airplanes making multipath signals, far out away from any land.

I guess that is still very optimistic - 15-20 m, ie 50-60 ft are more
like it.
If you use SDGPS with corrections by satellites, it might come down to 3
m, or 10 ft.
No way navigating a channel with 3 m leeway on each side by GPS (even
SDGPS). Tested! In perfect conditions ...

I've done considerable testing of my modest Magellan Sportrak Color, and
with a clear view of the sky it's repeatable to within 10-20 feet, even
in major metro areas, quite capable of navigating real world narrow
channels, albeit not as narrow as your hypothetical case of 3 m on each
side.

--
Best regards,
John Navas http:/navasgroup.com