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Russian GPS Alternative Near Completion
Russia has successfully launched another round of GLONASS satellites bringing the grand total to 18 of the navigational units online. "The GPS competitor -- first begun in the Soviet era and only recently revived after years of post-collapse neglect -- is now theoretically capable of providing coverage to the entire Russian territory, with First Deputy Prime Minister Sergei Ivanov claiming that the first compatible consumer devices will be available in the middle of next year. By 2010 Russia plans to open the system up to outside nations as well, contributing to an eventual three- or even four-system global market"
My own experiments with GPS would bear this out.
When I was doing more of this stuff, clients would sometimes take several GPS points, and find to their delite that nearly always the three points were much closer than the supposed precision of plain old non-differential GPS. As a result, they began to assume the system had more precision than rated.
Intrigued by this I set up a fixed station that tracked all the fixes coming out of the receiver over several hour period. What I found is that sequential readings tended to be strongly correlated to their immediate predecessors but weakly correlated to fixes taken much earlier. Essentially the receiver would report all the points as being in a smallish bucket a couple of meters wide, but every fifteen or twenty minutes it would pick up the bucket and put it a different place five or even ten meters away. Then there'd be a run for fifteen minutes or so at the new "bucket position", after which the bucket would move once again.
The way I interpret this is that the various sources of error change as a satellite's position changes. Perhaps a mountain range gives a strong reflection in one position or not another, or perhaps a new satellite rises (or an old one sets), leading to a whole new set of data.
So, it stands to reason that having more than twice the number of satellites means that the various random sources of error would tend to be averaged out more, provided any difference between the old and new system could be accounted for systematically.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
For those of us in land surveying, having another few satelites is very important if your in a hurry. My current equipment (Topcon Hiper-lite) can obtain accuracy of less than 1 cm in less than 2 minutes just using the US GPS satelites and more accurate in less time using both US GPS and Russian GLONASS. Also, here are a few other interesting facts associated with GPS for Surveyors (who need sub-centimeter accuracy) 1) The more satelites the better (and my equipment which happens to be rebadged JAVAD) has been getting signals from GPS and GLONASS for a few years already, 2) The US stopped encoding the GPS signals under executive directive a year or more ago, and 3) The Eurpoean Union is working to put up their own GPS network which the latest generation of commercial survey grade receivers are already prepared for. So, for those of us whose business requires GPS, the article seems to be more about political posturing and less about anything new system-wise.