'WAS' enabled

[CacheReward]

What is the advantage if there is one to disabling the WAS capability on a GPS? Thanks

[+FireCacher]

Typically more satellites. For example, if you can see 4 WAAS birds and 7 standard birds, your unit will use the 4 WAAS birds and possibly have worse precision than the 7 standard birds. Otherwise, not much, battery usage seems to be very close with or without WAAS enabled.

[+MrGigabyte]

As you did not mention which model of GPSr you are referring to, I will address the advantages as they apply to Garmin's.

 

With WAAS off...

You free up 2 channels that can be used to receive signals from 2 more birds.

 

You may switch your GPSr to battery saver mode as it must be normal mode to enable WAAS.

 

You will almost without exception, obtain better accuracy without it.

 

 

[+mrp]

The usefulness of WAAS a matter of some controversy around here.

 

What I can say, is that using an eTrex Legend, in Northern California (SF Bay Area to the Oregon coast), I haven't had much luck with it. The satellites are too low in the sky to reliably receive using the little patch antenna.

 

However, people using units with better antennas and more recenet hardware and software (notably the Magellan Sportrak), have had great luck with it.

 

Even if you have a Legend (or Vista or Venture), it may work better for you in Texas becuase the North American WAAS satellite should be relatively high in the sky, and especially in west texas you have clearer horizons.

 

-- Mitch

[+MrGigabyte]

quote:

---

Originally posted by FireCacher:

if you can see 4 WAAS birds

---

 

At present there are ONLY two geo-stationary satellites serving the WAAS area (Inmarsat IIIs: POR (Pacific Ocean Region) and AOR-W (Atlantic Ocean Region-West).

 

Garmin units allow for 19 WAAS unique GEO satellites as specified by the FAA TSO C-146.  They are depicted on the GPS as Satellite IDs 33-51 which is actually a NMEA convention.  Each WAAS satellite has its own unique PRN code assigned from the list of 19. 

 

Garmin receivers use one or two channels to track WAAS satellites and they will use the WAAS satellite in the position solution, if the WAAS system indicates it is OK to use for navigation (sometimes the WAAS satellite is flagged as "do not use for navigation" but the corrections are still useful).

 

Inmarsat POR = PRN 134 = Garmin Satellite ID 47

Inmarsat AOR-W = PRN 122 = Garmin Satellite ID 35

[+TeamCNJC]

(I'm sure I'll be corrected if I'm wrong here, but... )

 

Aside from being able to pick up reliable WAAS signals, you also have to be in proximity to a WAAS ground station. The ground stations receive the "raw" GPS signals, calculate the error, and upload the error correction to the WAAS birds, which transmit the error correction back down to all WAAS-enabled GPSr units. When you are receiving an error-corrected signal in a Garmin unit, you will see a "D" in the bar indicating differential signal.

 

Bottom line - if you're not close to a ground station, the error correction is not valid, and you will not improve accuracy.

 

-Craig/TeamCNJC

[+TeamCNJC]

(I'm sure I'll be corrected if I'm wrong here, but... )

 

Aside from being able to pick up reliable WAAS signals, you also have to be in proximity to a WAAS ground station. The ground stations receive the "raw" GPS signals, calculate the error, and upload the error correction to the WAAS birds, which transmit the error correction back down to all WAAS-enabled GPSr units. When you are receiving an error-corrected signal in a Garmin unit, you will see a "D" in the bar indicating differential signal.

 

Bottom line - if you're not close to a ground station, the error correction is not valid, and you will not improve accuracy.

 

-Craig/TeamCNJC

[CacheReward]

So, you are saying that I will have better accuracy with WAAS disabled?

quote:

---

Originally posted by MrGigabyte:

As you did not mention which model of GPSr you are referring to, I will address the advantages as they apply to Garmin's.

 

With WAAS off...

 

+ You free up 2 channels that can be used to receive signals from 2 more birds.

 

+ You may switch your GPSr to battery saver mode as it must be normal mode to enable WAAS.

 

+ You will almost without exception, obtain better accuracy without it.

 

 

http://www.geocoins.ca

[+TeamCNJC]

I think it depends on the model of GPSr. From what I've seen posted here before, it seems that the Maggies are able to deal with intermittent WAAS signals while the Garmins seem to choke a bit. What are you using? -Craig/TeamCNJC

[+fizzymagic]

quote:

---

Originally posted by CacheReward:

 

So, you are saying that I will have better accuracy with WAAS disabled?

---

 

That's what he is saying, but he is mostly wrong.

 

To review his points:

 

Frees up 2 channels -- this only is a problem if your unit is receiving more than 10 satellites, which I have never seen.

Uses up batteries -- only applies to Garmin units with power save on.

Better accuracy without it -- If the WAAS corrections are not applicable to all visible satellites, most units will only use the ones with WAAS corrections, which gives you reduced precision as reflected by the EPE on the screen. If you are near a WAAS ground reference station then your accuracy will probably be better with WAAS on, at the possible cost of reduced precision from fewer satellites used. Near you, there is one in Fort Worth and one in Houston, so for most of Texas the WAAS corrections should be quite good.

 

It is quite clear that the poster who gave you this advice does not understand the difference between accuracy and precision.

 

The thing you need to understand about WAAS and geocaching is that most geocaches were placed by people without WAAS, and the errors between your unit and theirs add incoherently, which means that you probably won't notice any improvement in your ability to locate geocaches with WAAS on. This fact, along with the misleading reporting of EPE done by most GPS receivers, leads people to believe that the accuracy without WAAS is better. But they are, for the most part, wrong.

 

If you want to test the impact of WAAS on accuracy in your area, there is a simple test you can do. Find a trangulation point (not a benchmark) that you can get to from the benchmark hunting portion of this website. Make sure that the coordinates of the point are not obtained by scaling. The positions of most triangulation points are usually good to a few centimeters. Then go to the location and see how far off your GPSr is with and without WAAS corrections on. Be aware that it takes approximately 10 minutes for the WAAS system to initialize in your GPSr after it acquires the WAAS satellite. Do this experiment several times, and you should be able to see the difference, if there is any.

[Couch_Potato]

quote:

---

Originally posted by TeamCNJC:

(I'm sure I'll be corrected if I'm wrong here, but... )

---

 

You're wrong

 

Just kidding As I understand DGPS and WAAS you have it right. However, some of the differential infomation is the satellite's positional error and clock error which are independant on location and should improve accuracy anywhere.

 

I'm probably wrong here and I'll hear about it, but I believe DGPS and WAAS were originally intended for naval application. Meaning that most of the ground stations are along the coasts, which is convenient since the WAAS satellites are over the oceans.

 

I'm not lost!

I just don't know where I am.

[Couch_Potato]

quote:

---

Originally posted by TeamCNJC:

(I'm sure I'll be corrected if I'm wrong here, but... )

---

 

You're wrong

 

Just kidding As I understand DGPS and WAAS you have it right. However, some of the differential infomation is the satellite's positional error and clock error which are independant on location and should improve accuracy anywhere.

 

I'm probably wrong here and I'll hear about it, but I believe DGPS and WAAS were originally intended for naval application. Meaning that most of the ground stations are along the coasts, which is convenient since the WAAS satellites are over the oceans.

 

I'm not lost!

I just don't know where I am.

[+mrp]

quote:

---

Originally posted by fizzymagic:

+ Frees up 2 channels -- this only is a problem if your unit is receiving more than 10 satellites, which I have _never_ seen.

 

---

 

I'll make this one correction... It makes a difference if your unit is TRYING to receive more than 10 satellites, which is pretty common. While I've never received signals from more than 7-8 satellites at once, I've often had all twelve channels dedicated to satellites above the horizon, and it's difficult to predict which ones it will be able to pull in at a given moment. With WAAS on, two of those satellites are taken out of the search, and if either or both of those two could be pulled in, then it might the difference between a 2D and a 3D solution, or wheter I keep lock or not. Like I have said before, on the etrex line, I have almost never seen WAAS work in California, and losing those two channels can make the difference between keeping lock in tree cover or not. Therefore, if you don't regularly see the "D" appear in the sat bars, it's better to turn it off. All the evidence points to WAAS working great in some other units (including the SportTrak and probably the GPS V as well), but with a Legend, Vista, or Venture, I haven't heard of it being useful.

 

quote:

---

It is quite clear that the poster who gave you this advice does not understand the difference between accuracy and precision.

---

 

I've got to disagree, as one who taught this distiction(*). The precision is unaffected (except in the lower EPE), since that is a function of the granularity of the readout, and is unaffected by WAAS, whereas accuracy is a question how close the position is to the "right" position. The poster in question was indeed talking about a decrease in accuracy. I can't think of a reason why sucessfully receiving WAAS in the US would decrease accuracy, but there has been some anecdotal evidence to that effect for people trying to use WAAS in Europe.

 

One thing to keep in mind, is that WAAS is not simply a larger scale beacon-station DGPS. It uses the information from the ground station to develop a more detailed model of ionospheric distortion as well as clock and empheris corrections for each SV. While this isn't subject to the same sort of simple degredation as you get when further from a beacon station, it's possible that the ionosphic model it generates becomes badly flawed for locations far from ground stations (say.. in Europe).

 

-- Mitch

 

(*) An example for those who haven't thought about the distiction. If my GPSr told me I was somewhere near San Francisco (Say N 38 W 122 +/- 2 degrees in either direction), it would very accurate, but not terribly precise. if it told me I was 2.5 ft. west from the NW corner of Gouchestishire Rd and Cromwell Lane in London, it would be very precise, but not at all accurate.

[+apersson850]

I haven't been anywhere where WAAS is active, so I haven't had any chance to see any difference in accuracy. However, I can easily tell that having WAAS enabled takes quite a lot of CPU power from my Vista, since everything else is more sluggish than without WAAS enabled.

 

Maybe this is because the unit has a problem trying to figure out the non-operative EGNOS system here in Europe, but I recall that I've read about the performance impact WAAS has on receivers in North America too.

 

By the way, I saw that almanac data for satellite #44 (IOR, Indian Ocean Region) has entered my receiver for the first time a few days ago. Previously, only #33 (AOR-E) was found by the unit.

Still, these EGNOS satellites don't transmit any valid data.

 

Anders

[+phantom4099]

On magellan units disabling WAAS does not free up the two channels, it only stopes the use of the corrections in the solution (unit still gathers info from them). The 2 channels that WAAS occupies would only be used for the sats nearest the horizon (most errors in them). A little tid bit about the sat screen it that the sats on the left are highest in the sky, and those on the right are nearest the horizon.

 

Wyatt W.

 

The probability of someone watching you is directly proportional to the stupidity of your actions.

[Kerry.]

WAAS is as yet a $6 billion system that has yet to be completed, only services a small part of the world (compared to GPS as such) and really was never intended to be used in a handheld running around in the forest.

 

Loosing 2 channels from most 12 channel recievers really doesn't make or break 2D or 3D navigation and besides the % of time 12 satellites (or more) are available is reasonably low compared to the designed average. Besides we are a little spoilt having 28 operational sats and system specs modelled around 24.

 

Actually if antenna and/or software was designed to be the most effective there probably wouldn't be a need for 12 straight GPS channels at all.

 

Put simply WAAS shouldn't be used outside the ground station network even though one can actually recieve the signal as this link shows

 

http://www.cqnet.com.au/~user/aitken/a116_117.jpg

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[Kerry.]

WAAS is as yet a $6 billion system that has yet to be completed, only services a small part of the world (compared to GPS as such) and really was never intended to be used in a handheld running around in the forest.

 

Loosing 2 channels from most 12 channel recievers really doesn't make or break 2D or 3D navigation and besides the % of time 12 satellites (or more) are available is reasonably low compared to the designed average. Besides we are a little spoilt having 28 operational sats and system specs modelled around 24.

 

Actually if antenna and/or software was designed to be the most effective there probably wouldn't be a need for 12 straight GPS channels at all.

 

Put simply WAAS shouldn't be used outside the ground station network even though one can actually recieve the signal as this link shows

 

http://www.cqnet.com.au/~user/aitken/a116_117.jpg

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+JetSkier]

quote:

---

Originally posted by phantom4099:

On magellan units disabling WAAS does not free up the two channels,

---

 

I have a Magellan Meridian and there is no way to disable WAAS. Which Magellan has this capability? Which one do you use?

[+TeamCNJC]

quote:

---

Originally posted by JetSkier:I have a Magellan Meridian and there is no way to disable WAAS. Which Magellan has this capability? Which one do you use?

---

 

Try this thread here.

 

-Craig/TeamCNJC

 

[This message was edited by TeamCNJC on July 01, 2002 at 01:02 PM.]

[+phantom4099]

You can also activate and deactivate WAAS while your unit is on. TO do this hit menu, then right-left-right-left. change that to 03 and disable WAAS. Then hit the ESC button twice to get back to the screen that you started from.

 

Wyatt W.

Any one know how to get rid of my avator?

 

The probability of someone watching you is directly proportional to the stupidity of your actions.

[+JetSkier]

Thanks TeamCNJC and Phantom4099! Works great! As a software developer, I should have known there would be a "back door"! Anyway, I can now turn it off, but I'm not conviced that it should be off. Everything I've read indicates that with WAAS turned on, your coordinates are closer to being exact. I know that if someone places a cache and reads coordinates without WAAS, then my having WAAS on doesn't get me any closer to it, but I'm going to keep mine on.

[+TeamCNJC]

... that you try an on/off approach to see if there's any different, but I got bored at work today and ordered a MeriPlat, so now I can try it myself.

[+TeamCNJC]

... that you try an on/off approach to see if there's any different, but I got bored at work today and ordered a MeriPlat, so now I can try it myself.