On Sat, 16 Jul 2005 10:30:26 -0700, Peter Bennett wrote:

On Sat, 16 Jul 2005 08:43:33 -0400, Anchor
wrote:



There seems to be some confusion between WAAS and DGPS.

Yes, I can see that from your message...

WAAS is on on some GPS satellites, not all. If a GPS can see a WAAS
equipped satellite, it has WAAS information for that satellite. Clearly
if a satellite, WAAS or non WAAS, is in shadow the GPS cannot use that
satellite. A WAAS GPS will need 3 or more WAAS satellites to produce a
WAAS fix. Three or more satellites but less than 3 WAAS satellites in
view generates an ordinary fix. This has nothing to do with whether or
not you are in harbor.

WAAS correction data is transmitted by two (Inmarsat?) geosynchronous
satellites, not by any of the normal GPS satellites.

WAAS collects correction data from a network of reference stations in
the US, and uploads that data (after some processing) to the
satellites for rebroadcast. The correction data is only useful at
location inside, or near, the reference station network - if you
attempt to use the data in distant locations, you may increase
positioning errors, rather than reduce them.

Some GPS manufactures refer to a WAAS fix as a differential fix. This is
a poor choice of nomenclature because a WAAS fix is a WAAS fix, not a
differential DGPS fix.

WAAS is a form of differential correction, so I believe it is valid to
consider a WAAS-corrected fix a differential corrected fix.

I was mistaken about the satellites.

WAAS does not use GPS satellites.

http://gpsinformation.net/exe/waas.html

Our Garmin 76 reported WAAS GPS fixes on the east coast of Australia and
New Zealand in late 2002.