WAAS in gpsr?

[rfriel1]

does WAAS do anything in a gpsr? i haven't heard much talk about WAAS in this forum. is WAAS totally useless and not worth any gpsr that is WAAS enabled?

any ideas or opinions?

[+CCrew]

Higher resolution of your position. Provided you can see one of the birds :-)

 

If Wal-Mart is lowering prices every day, how come nothing in the store is free yet?

[Kerry.]

quote:

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Originally posted by CCrew:

Higher resolution of your position. Provided you can see one of the birds :-)

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No, not only must one be able to see the WAAS sats but you MUST also be within the WAAS ground network stations (apart from other conditions).

 

Outside that ground network those WAAS sats can be seen from many parts of the world and all the WAAS signal does (outside the ground stations) is decrease accuarcy (big time).

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Renegade Knight]

WAAS does work, it does increase your accuracy (including your GPS's reported accurace (at least on the GPS V). However it slows down your GPS due to the overhead of the WAAS calcuations and the increased accuracy isn't a real benifit in Geocaching. I leave my WAAS off. The slowdown in updates etc. is more annoying than the benifit of WAAS.

 

Wherever you go there you are.

[+MrGigabyte]

Here are the current (WAAS) ionosphere correction ground station locations.

 

http://waas.stanford.edu/tmslive/graphics/screen1.gif

 

The total accumulated corrections from valid differentially corrected WAAS data is 7m. The majority of the errors are ionospheric-delay errors. The balance are clock and orbit.

 

As Kerry points out, you will receive all the corrections, regardless of where you are. Orbit and clock will be valid everywhere, as they relate to the SV's themselves. The ionospheric-delay errors will not be corrected "correctly" if you are outside the correction area.

 

Also, a big factor is how the GPSr interprets the received corrections. Garmin does not apply any correction adjustment for positions outside the correction area as many other manufacturers do. Also, Garmin receivers do not consider non-DGPS signals with ones that are receiving corrections. This will inevitably make the position solution worse.

[+EraSeek]

And where is the correction area? It is my understanding that the correction area covers all of the US. The stations collect the data, then create a uniform model from that data that covers the US. That is the beauty of it and how it differs from DGPS. The experts:

 

("WAAS system will generally be more accurate than beacon based DGPS because of the way the corrections are rendered by the WAAS system and applied by the GPS receiver. The primary factor is spatial decorrelation, which is the degradation of corrections due to separation from the reference station. RTCM based DGPS corrections suffer from spatial decorrelation, but WAAS corrections do not." )

 

You see, WAAS collects the corrections from the stations, then makes a tight uniform model of the ionosphere disturbance across the US, and relies on your GPS to apply the model to your current position. I read somewhere how tight this net of corrections is, and how it will adjust to the nearest points of the model if it is between these tight data points. There is also a GIF that I've seen showing how the ionosphere moves like a large wave throughout the day, which would basically correspond to the WAAS adjustments. I'm I wrong on this?

 

[+EraSeek]

Here is the helpful page:

 

http://celia.mehaffey.com/dale/dgps.htm#waas

 

Read the page from here down and view the grid:

 

(Clock and ephemeris data is specific to a satellite but ionospheric errors are specific to your location therefore they must be sent separately. After receiving raw data from each of the ground station the master station divides the country into a grid and then builds ionospheric correction information on a per grid location basis from the data received from each reporting station. It is this grid location that is used by the gps receiver to determine the applicable ionospheric corrections)

 

I believe you where referring to the statement about Garmin below. Note that he points out that if you are in South America, outside the coverage area

 

(If you receive a satellite but do not have any ionospheric data for your area the Garmin receivers seem not to detect this condition. They will happily switch to differential correction mode and supply zero ionospheric corrections. This can cause the unit to show larger errors with WAAS enabled than without. I think they should apply the internal ionospheric correction algorithm in this case but they don't seem to. So if you live in South America with no WAAS corrections be sure and turn WAAS off. )

 

[Kerry.]

The "effect" of having WAAS turned ON outside the ground station network.

 

everybody keeps telling me where to go

[+EraSeek]

Yes. And this was Australia. Which is outside the US.

 

[+EraSeek]

in answer to the original question, Yes, WAAS is worth it if:

1. you want bouy bumping accuracy

2. you have good exposure to a WAAS satelite

3. you are within the US

4. you don't mind using up batteries a lot quicker

 

otherwise it is a Geewizz kind of thing.

 

[+Gimpy]

quote:

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Originally posted by rfriel1:

does WAAS do anything in a gpsr? i haven't heard much talk about WAAS in this forum. is WAAS totally useless and not worth any gpsr that is WAAS enabled?

any ideas or opinions?

---

 

I guess it all depends on what you're doing with your gpsr. My guess is that if you're going after benchmarks, waas might give you a bit of an advantage, because the co-ordinates for the benchmark were probably taken with some sophisticated equipment. But for geocaching purposes, I would think that the majority of caches were given listed co-ordinates that were taken off non-waas equipped gpsr's. If that's the case, I don't see where waas would be of any help. Throw in an overhead canopy of tree cover, & I'd have to believe that the wass bird(s) would be that much more difficult to lock on to anyway. 2 of my gpsr's have waas, but I leave it turned off on both. Nothing real scientific about my rationale. I figure it just makes sense. Could be wrong. It's happened once or twice.

 

"Gimpy"

[+apersson850]

In Europe, SBAS is coming in 2004 or so, but they did a test a week ago of the EGNOS system.

 

In the main road in a small village in Switzerland, with buildings blocking part of the view of the sky, I could get six differentially corrected satellites, including the AOR-E itself. That gave a predicted accuracy of four (4) meters.

 

Later that week, when the test was over, I got signals from ten (10) ordinary satellites in an open area a bit above the village. Predicted area four (4) meters.

 

Conclusion: If you do get signals from any SBAS, be it WAAS or whatever, it may be able to enhance your accuracy to a level that otherwise would require far more satellites to achieve. Or at least it predicts so, to make you feel happier about your investment.

 

Anders