Is National Differential GPS Lost? 109
Nealix writes, "This article at GPSWorld reports that National Differential GPS (NDGPS) is endangered in the 2007 budget. This has ramifications for a variety of government programs such as the Intelligent Transportation System and Positive Train Control by the Department of Transportation. Blind people and robots also benefit from highly accurate GPS navigational capability provided by NDGPS, which appears to work better in the urban canyons. If NDGPS loses, the winner would appear to be the FAA-backed Wide Area Augmentation Service (WAAS). Of course, what would be really cool is to see more GPS sites around the country make DGPS data (RTCM) available over the Internet."
Doom and gllom for punchcards! (Score:5, Informative)
I didn't mind punch cards being phased out either....
Re:Why don't they just publish the P(Y) keys? (Score:4, Informative)
DGPS can be far more precise than military precise setting. A resolution of one meter is more than good enough for any weapon system that would use GPS.
I remember hearing about a form of DGPS that has a lot higher resolution than one meter. It is often used for surveying.
Re:DGPS sites on internet (Score:3, Informative)
Re:Why don't they just publish the P(Y) keys? (Score:4, Informative)
That being said P code recievers make differential and carrier differential easier.
Re:Not wishing to flame (Score:3, Informative)
The use of "GPS" and "WAAS" does make it clear. The FP did not say "GLONASS", or "EGNOS", or "GAGAN", or "MSAS", or even the generic term "SBAS".
The whole world can use GPS, but the US outright owns it and controls every aspect of its operation, whether the rest of the world likes it or not. Dubbya could order SA turned back on tomorrow, and all the foreign users that have come to critically require reasonably accurate GPS would have no say in the matter whatsoever.
used by hundreds! (Score:5, Informative)
On top of this, WAAS isn't the end of the line, there are more systems coming on-line that will improve GPS acuracy even more. The old system was OK for what it was, but the need for extra receivers by each user certainly limited it's adoption. It should be phased out.
And one thing I just have to comment on from the article and even the /. blurb: "Positive Train Control"! Are we really to believe we need taxpayer funded meter accuracy for GPS for train control? Do these trains really wander from from the tracks we know the location of? Isn't normal GPS accuracy just fine for choo-choo trains? And in the rare cases where higher accuracy might come in handy (although should hardly be needed), such as a switchyard, couldn't the location itself provide a small simple system for far less cost than asking the taxpayers to support it for this special use? You don't even need Internet data for this, you just have to agree on the location of the stationary differential receiver site and put a receiver without WASS there, it's error from it's known location is the same or better correction information than you could get from the Internet.
Re:You Know, This Kind of Is a Problem ... (Score:3, Informative)
Now you're telling me that we can't afford to clip another $10 million off the Defense budget and give it to this service (which may, arguably, help the coast guard in defending our shores)?
This kind of DGPS (type-1 or type-9 messages only) that the Coast Guard sends is of very limited utility. Now that "Selective Availability" (intentional noise added to the civilian GPS signals) is gone, there is very little positional improvement one gets from their DGPS. If they kill it, I doubt anyone but the folks working there will be affected in any significant way.
Re:Of Course! (Score:3, Informative)
Differential GPS greatly improves your precision, from meters to centimeters, but you don't really need that to give directions. You'd want it if you were actually letting the thing steer your car, but we're not there yet.
There is no need for NDGPS. How WAAS works (Score:3, Informative)
Just to explain to the submitter if this is not already crystal clear: There is no need for NDGPS. WAAS has fortunaltely replaced it.
NDGPS required a seperate receiver to get the error signal from a ground based transmitter. You also had to be near a ground based error transmitter for this to work.
The ground based error transmitters are still there, and more are beeing added. Instead of transmitting locally, a database of errors over a wide area is constructed, and a geostationary sattelite transmits the error database on the same wavelenght as the other GPS sattelites to all GPS devices. All that is needed for this is typically a firmware update in the GPS unit.
Simple, effective, cheap.
Re:Doom and gllom for punchcards! (Score:4, Informative)
Re:Of Course! (Score:3, Informative)
Welllllll...
Actually most consumer devices ALSO uses WAAS. Plain old satellite is "just fine" even without WAAS, but WAAS really helps refine the position.
Especially in the "urban canyons", normal GPS signals are pretty bad at times. Get in the city around tall buildings, and you'll see your accuracy get into the hundreds of feet if only three satellites are in view and lots of signal reflections are muddying the data. That's enough to put you a block away from your actual location. So WAAS or DGPS really helps in those situations. Sure, out in the middle of a cornfield in Kansas, you might not care about DGPS, but in that case you often have eight or ten satellites available and an accuracy of perhaps 15 feet. Not in the middle of the city.
NDGPS just better for some applications (Score:2, Informative)
1. Sky visibility can significantly degrade your accuracy via WAAS. Personally, working in a lot of areas with random overhead cover (trees) I prefer NDGPS to WAAS even if I have to download the corrections and post correct. In a test I ran in a suburban forested park NDGPS was able to meet the 1 Meter accuracy claims even with heavy overhead (40+ foot trees)in a comparison vs 6inch pixel aerial photography. WAAS consistantly got a ~2-5 meter error on the same locations.
2. NDGPS stations are already failing in our area. Of the Three stations that are barely within the range at which they are useful, none consistantly provide base station data via the internet, and 1 has failed completely. If the current funding level is approved ($0) I don't see any improvement in the near future. Thus my company has invested in our own DGPS base station to guartee 1 meter accuracy in the event of NDGPS unavailability, despite the downsides (maintenance, requires a survey accurate point to permenantly mount the basestation, basestation must run at least one hour before and after field collection of data to insure coverage).
3. In our current contract with a US government agency that specified 1 meter accuracy GPS, WAAS was not an acceptable correction option. So it was either rely on unreliable Government funded base stations, or buy our own. (BTW, I'm glad we did buy our own).