On Jun 25, 6:14*am, "Tim Springer"
wrote:
Read the article I wrote on the SVN 49 issue. It is out on the Inside GNSS
"frontpage" (http://insidegnss.com) now and will be included in the
July/August printed version

The article nicely shows and explains what is being done and why that works
(for "ordinary" users).

For the direct link to the article visit my blog at:http://gnss.servolux.nl/gnss_blog.html

Tim

A satellite error less than a meter is significant for the Standard
Positioning Service (SPS) in that it's small enough to be swamped by
uncertainties introduced through ionospheric transit delays. Of
course, its more significant for two frequency systems that actually
attempt to measure the the delays.

Practically speaking, my SPS accuracy is typically 15 feet (4.6
meter) on the open water at the Chesapeake Bay (N 39 deg). That's
good enough to find a mark in poorest visual conditions. That's
really good enough for car navigators; my TomTom map database is often
less accurate than GPS. I'd also say its good enough for locating
trains also but I would hope the actual train movement is also
controlled by state-of-art signaling systems.

We know FAA operates WAAS for landing airplanes (SPS) and has
estaplished approach procedures for most North American airports.

http://www.nstb.tc.faa.gov/RT_Vertic...ctionLevel.htm

I'd hope the conventional Instrument Landing System (ILS) is retained
as a cross check. ILS has served us for over 50 years.

I haven't noticed any important improvement in horizontal accuracy
with WAAS. Perhaps vertical accuracy is improved but I haven't
studied that. A major criticism of NAVSTAR is an inability to convey
real time information about individual satellite health. WAAS
attempts to solve this problem by immediately instructing receivers
to ignore out of tolerance satellites when the Ground Segment detects
a problem. Every satellite now receives continuous monitoring through
an expanded ground network so malfunctions are quickly detected.

The Air Force cannot 'Tap Dance' around accuracy degradation by hiding
behind self imposed easy to meet specifications. They might retain
technical control but they have lost political control. The world will
not buy that act.

--- CHAS