WAAS Technology in GPS???

[Tracey]

Iam looking at purchasing a hand held GPS and have encountered some confusion on GPS's with and without WAAS tech. A salesman for Reeds at the Des Moines sports show last weekend told me a ordinary GPS without Waas was just as accurate as a GPS with Waas. He said the government recently quite scrambling the frequencies so they have the same accuracy?? Is this true?? If this is true whats the selling point of Waas? Thanks for your help!!!!

[rock2me]

Not necessarily true. Go to this website to read more about how WAAS works: http://gps.faa.gov/Programs/WAAS/waas.htm


Good Luck!

[EyeJacker]

Selective Availability(SA)was the goverments method of degrading the accuracy of civilian GPS receivers. SA was eliminated by President Clinton in MAY of 2000. Picking up a WAAS satilite signal can improve your accuracy from an average of 15 meters (49.2 ft) to approx. 3 meters or about 10 feet.
Jack

[Thom]

He was wrong. That part is simple. The claims for accuracy for GPS units, with WAAS or without, or even with differential or without, tend to be all over them map, and usually overly optomistic by far, but in absolute terms WAAS beats out non WAAS every single time - when its working.

Of course that has to be the case if you think about it even a little bit. but back to the point. About a year and a half ago, when the country still had a President who was elected by the people (who wasn't owned lock-stock, and barrel by oil industry companies -Enrron!), President Clinton ordered that Selective Availability (SA) turned off, this was the system that degraded GPS signals. Before he got rid of SA the accuracy of GPS units ran at within 100 meters 95% of the time. When SA was turned off the accuracy of GPS units became much more a matter of the quality of the GPS unit itself, not artificial scrambeling of the signal. The typical GPS unit at that time could get accuracy down to about 10-20 meters. That's pretty good actually. All that time there was the ability to inprove the accuracy of you GPS by simply connecting it to a differential unit. With differential units there is a separate receiver that is connected to the GPS. In some units the receiver was actually built into the GPS, but it was still a separate receiver. This receiver got signals that improved the accuracy of the GPS units. Here's how they did that. Around the nation, generally at the coasts but on some rivers too, there are GPS receiving stations located at precisely known locations. They run constantly and monitor the difference between the location the GPs satilites indicate for them and their known location. They then compute corrections and broadcast that information. Your differential receiver could then accept those corrections and apply them to your positon fix. Of course you were not at the same place as the differential station so the corrections were not dead accurate but they certainly helped an awful lot. With differential you could get improvements in accuracy down to about 10 meters most all of the time and even down to about 5 meters much of the time. One of the problems with this system is that although it was very good for horizontal accuracy it didn't do a whole lot for vertical accuracy. Airplanes need the vertical accuracy if they are to land without big bumps. So the FAA looked to another way to improve accuracy of GPS units for aircraft. The results of their work was the WAAS system. Now in truth the WAAS system is very much like the differential system, and in fact it actually uses many of the same ground reference stations. The main difference between differential and WAAS is that once the errors are determined by the ground stations that information is sent back up into space to two specialized satilites (one in the Atlantic and one in the Pacific) which then send the correction information back down to earth. This is very good for aircraft who almost never have their view of the sky blocked. It also works pretty good for boats. Here's the rub though. In terms of absolute accuracy the WAAS system isn't really very much better than the differential system. While you will see claims all over the place of 3 foot accuracy with WAAs don't bet on it being the case. Something more on the lines of 3-5 meters is a lot more like it. So what's the main claim to fame for WAAS? Easy, its cheap. Think about it, the WAAS system is really one that operates by improved software. Its using the same GPS satilite constellation, with the two enhanced satilites, but its still the same system. You don't really need a second receiver to use WAAS, just a receiver that has the ability to decipher the WAAS signals.

So, real world, what does WAAS get you? Well, its better by a good margin over plain old GPS, its just slightly better than GPS plus differential though. I was running a plain GPS with differential (a Garmin GPSMap-210) connected to a differential receiver right next to a WAAS receiver (Garmin GPSMap-76) last year for a few months. I already had the 210 and differential and had just got the 76 for backup. The 76 has a builtin antenna of course (its a hand held) and it was mounted about 3 feet away from the GPS antenna for the fixed mounted 210. At any given time they would both give the same position location numbers. They did this virtually all the time. So, because the numbers were the same, and I have to assume that the number itself was accurate, I can not tell you that the WAAS unit was a single bit better than the differential unit. Now of course if I had turned off the differential signal to the plain GPS that would have changed but then if I had turned off the WAAS corrections to the hand held it would have become the less accurate of the two. Oh, and you should know this too. If you turn WAAS on in one of the hand helds it decreases battery life. Running that WAAS has its cost.

So that's about it. WAAS is nice, it costs very little more than plain GPS and it does give improved accuracy. It eats batterys a bit faster in hand helds but that doesn't mean much of anything for a fixed mount unit. If I was buying a new GPS today I wouldn't even look at one that didn't have WAAS simply because its something that gives you very good bang for the buck. That help any?

Thom

[EyeJacker]

We know a "Quid Pro Quo" existed between "Slick" and Enron, it has yet to be proven that one exists or existed between George and Enron. The fact appears to be that Enron had money for most everyone who was anyone. Sounds like sour grapes to me. What happened to the no politics WC rule?
Jack
P.S. Remind Bill to wash his hands if he plans to do any fishing!:)

[Tracey]

Thanks for the info. I thought from what I had read that Waas was the better bang for a little more money, I didn't argue my thoughts with the salesman because it appeared they were promoting older Lowrance units with out the capabilities of Waas. Thanks again ,now I need to determine which unit will fit my needs. One other thing that was impressive was a demonstration at the Lake Master booth on their mapping software so that will be a consideration with the hand held selection. The map with the 1ft contours of Mille Lacs was impressive. Thanks again for the replies!!!!!!
Tracey ,

[JBL]

That is a very informative post on GPS issues. I'm not sure that many are interested in the political propaganda though.

[Phil T.]

You didn't suspect he had some non-WAAS capable units he wanted to get rid of? I've been told by sporting goods salesmen that their DGPS-capable units were the perfect thing for me in the middle of ND. The nearest DGPS station is near Minneapolis/St.Paul.
Caveat emptor.

[john]

Thom,

Informative post on GPS details, you know your stuff. You can however leave your political opinions to yourself, and we'd be all better off.

[Sparky]

Before you talk about who is owned by the oil companies, check the facts and see who received the most money from Enron and visits to the White House.

[Thom]

Actually there may be more to it than meets the eye. The last time I read up on it there were 34 ground stations (with more planned) that supplied correction data for the WAAS system. Most of them were actually the same sites as used by the differential transmitters. Now what's important is this. The GPS satalites aren't geostationary. So from one minute to the next you may have different birds in sight. The same is true for the correction stations and it is not at all uncommon to see that your GPS will have some birds in view but not be getting any WAAS corrections for them all. Its also a function of the GPS to pick the best set of satalites to use at any given time. Remember, just because your GPS picks up 12 satalites doesn't mean that its using them all, its not. So it a double wammy, first not all birds get WAAS corrections and second its possible that the ones that are getting WAAS corrections are not the ones that your machine is using at any given point in time. Now we'll make it even worse. It is the case with both differential and WAAS that the closer your are to the correction stations the better the correcton information can be applied to your current positon solution. But remember, most of those correction stations were established where the old Differential stations were (which also happened to coincide with the old LORAN stations in many cases). As you may know the vast majority of those locations are on the coasts. So what does that mean? Well simply put it means that WAAS is not as good inland as it is on the coastal areas. The correction stations are sending up data for the birds they have in sight and the birds they have in sight are the ones that can be seen from the coasts for the most part. Its just that simple. You really have to keep that in mind when you see the manufacturer's claims that their machines have 3-meter accuracy. Yes, in ideal situations they do, but when are you going to be in one of those ideal situations? For the folks in South Florida, Baja Oklahoma (texas), and southern California, pretty often actually, put put yourself in the middle of Nebraska and the likelyhood of seeing that sort of accuracy consistantly are pretty slim.

Thom

[Woodchuck]

new DGPS station (and I would assume WAAS) going to be put in by Brainerd, MN. Getting the land and permits to put up the tower have been in the paper this last year.

[Just fishin]

It is really aggrivating that you would polute this great site with your personal political issues! I was reading your post with great interest untill i got to your political garbage. Needless to say I didn't bother to read the rest of your post as your credabillity was completely destroyed. I don't come on this site for that kind of aggrivation. Why don't you keep that **it to yourself next time or get the **ll out of here.
****ole!

[Dave_WI]

It's a shame that the guy knows so much about GPS and so little about POLITICS..............

[rmitchel]

Right now I use a hand held Garmin eTrex -- the yellow version. I live in central Wisconsin, and fish primarily within a couple hours drive.

Will a WAIS gps do much for me? I primarily use the gps to mark honey holes, so that I can return to them.

Thanks

[rmitchel]

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