You are correct - WAAS only covers the US and most of Canada and Mexico.
WAAS at this moment in time is governed by a geosynced satellite. It too is
a US DOD system in cooperation with the FAA. It also has many of the same
issues of satellite differentials that are broadcast from satellites - line
of sight blockages count.
The FAA is still in test / early delivery of their WAAS augmentation system
and over time it too will improve. For our overseas guests, the WAAS is so
obvious a solution for plane and other navigation that it too will come to
their area - someday. A WAAS-like service is likely available most places.
These alternatives require fees and additional hardware for real-time
corrections. Pretty much all Garmins are RTCM correction capable.
Another alternative is to do a postprocessed correction. Only certain GPS
receivers provide the verbose form of raw satellite data needed. If a
suitable matching benchmark site can be found or established, results can be
very good anywhere. Garmin and Magellan have such solutions in very low cost
products.
Our group has used all sorts of diffential sources and methods over the
years in the pursuit of sub-meter field navigation on tractors and combines.
In my opinion and testing the WAAS is the best solution to date. It has
very stable and high quality corrections, is essentially free, and totally
transparent for the user - it just works. It also can be "turned-off" in
times of uncertainty.
For higher quality receivers like Trimble, sub-meter accuracy is readily
achievable. Even sub $300 Garmins do much better than their advertised 3m
WAAS guarantee.
FYI
MidNight Mapper
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Saturday, May 05, 2001 12:23 PM
To: [EMAIL PROTECTED]
Subject: MI-L GPS, reply
neil is correct on the new GPS units, but when you read the info carefully -
you will see the following warning/comment/note:
*The WAAS signal is currently available in the US only in open areas or on
the water
On land, I am not sure how large an area is considered an 'open area'.
Apparently, WAAS was developed by/for the FAA (federal aviation authority
for
non-US readers) for aircraft.
s. Figuers
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