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DGPSIP had its first birthday on Jan 17, 2000. Thats a year after the first server sent TCP/IP RTCM corrections from a Garmin GBR-21 across 10 feet of ethernet to another server (running in client mode) which sent the corrections onto a Garmin 12xl.
On May 1, 2000 the government turned off selective availability (SA). That basically allowed any GPS to have roughly the same accuracy as a differential gps that was listening to one of the free coast guard DGPS transmitters. Overnight (literally!!!) dgpsip became superfluous.
Am I sad that DGPSIP instantly became a dinosaur? Well a little. Its real purpose was political though. I wanted to be able to show the average person how badly SA was screwing up the signal of their GPS. Even long baselines seemed to have much of the SA "wandering" eliminated. It was a great tool for showing how "quiet" things would get when SA was off.
The problem was that even "short" 1000 km baseline could have short term biases of 8 meters or so when the sun was up. So in effect it gave someone a tool that allowed them to do quick short term relative measurements and so-so longer term measurements. (At these distances one could get better accuracy by doing a 24hr average of GPS's position.)
After the first version of the code was released I started to get lots of very enthusiastic EPE reports from all around the world. I didn't want to quell people's enthusiasm for experimenting -- after all I get a big kick out of turning people onto science and math. I did suspect that folks were waiting for hours to get the best numbers and then dashed those off to me. While it is nice to know how well something could work at its finest, I really wanted to know how well it would work on average. I added the built-in standard deviation calculator to the remote code and had the remote send back the calculated deviation on the lat, lon and height. For folks with a good sky view and within a 3000 km radius the standard deviation numbers were always better by a factor of 3 than the no dgps SA-active case.
What was most interesting about the whole experiment was the number of connections I got from *.mil and *.gov sites. At first it really weirded me out, especially the ones from bases that were controlling some aspect of GPS segment. ;-) Then I started getting friendly email from folks at the gov/mil sites asking how they could run this or that aspect of the various dgpsip programs. All the folks that sent mail were into using GPS's recreationally and were pleased as punch that their personal consumer-grade gps could be made to work as well as the military gear.
The email that made me smile the most came from a mil site that works directly with the gps SA errors. The operator made a point of mentioning that whenever the policy-makers come by the site he shows them the dgpsip server and points out how it works over a very large area.
I also got a request from a military training center that wanted to use a private dgpsip server running on their base behind a firewall to distribute correction signals to the fleet. That one made me laugh. I assume the rules for dealing with the crypto were so cumbersome that they would rather deal with RTCM corrections.
Well, its certainly been a fun year and a third. I don't plan on turning off the server any time soon. (After all what do I need the differential radio for now anyway?) I would like to thank the 10's of thousands of folks that have gone to the trouble to download the code and use the server. I'd especially like to thank the folks that have set up remote feed sites. These were invaluable for showing folks how good things got when you were really close to a reference site. I'd also like to thank the authors that have ported the client code to new platforms or incorporated dgpsip client code into their programs. This has made dgpsip available to quite a few more people than just the original code would have been. Lastly I'd like to thank all the folks that took the time to send email and ask interesting questions. The best way to learn something is to try to explain it to someone else. It is amazing how many holes and problems that uncovers with one's knowledge. I've learned a quite a bit about GPS that I otherwise might not have. Thank you folks! Its been fun!
-wolfgang
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wolfgang.rupprecht+web@gmail.com
(Wolfgang S. Rupprecht)
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