Waas On Or Off

[+The HERB5]

If WAAS is off will the GPSr find the satellites but not use/display them or will it not look for them at all ?

 

If I see a satellite higher than 33 (I think) can I then turn WAAS on or do I have to have WAAS on to see them in the 1st place ?

 

Same question, two different approaches ?

[+The Robin]

Well This is my first post so I hope it helps'

I have been following the EGNOS WASS thing anyway today I reset my geko, turned WAAS on and just now in Hertfordshire its found sat33 and ive got the DDDDDD's and accuracy7ft

!st time in 2 months of daily use

 

Thanks to everyone in this community for the interesting contributions on this forum

 

The Robin

[+Pharisee]

If WAAS is off will the GPSr find the satellites but not use/display them or will it not look for them at all ?

 

If I see a satellite higher than 33 (I think) can I then turn WAAS on or do I have to have WAAS on to see them in the 1st place ?

 

Same question, two different approaches ?

Don't know about anything other than the Garmin Legend that I use but if you turn WAAS on, then two of the twelve channels are assigned to the geo-stationary satellites and you'll be able to see if you get a lock on one. If you turn WAAS off, then all twelve channels are looking for the orbiting satellites ant you won't see the geo-stationary ones.

[+littlejim]

The European Satellite Services Provider (ESSP) site says

EGNOS initial operations will start as from July 2005.

True or False

[+The HERB5]

Don't know about anything other than the Garmin Legend that I use but if you turn WAAS on, then two of the twelve channels are assigned to the geo-stationary satellites and you'll be able to see if you get a lock on one. If you turn WAAS off, then all twelve channels are looking for the orbiting satellites ant you won't see the geo-stationary ones.

 

Thanx, question answered....

[+Skippy and Pingu]

Not being a techie and just thought that GPS was GPS, please can someone explain what WAAS is.

I looked on my Garmin Summit and I can't find anything that says turn WAAS on / off.

[+The Forester]

The acronym means "wide area augmentation system". In Europe it's also known as EGNOS.

 

It is a radio data transmission system which broadcasts corrections to the GPS data, thus improving typical fix accuracy from something like 5 to 10 metres to better than 3 metres.

 

Not all GPSrs are configured to use WAAS. If your manual makes no mention of it, then your unit is not a WAAS-capable one. Don't worry, WAAS is not necessary for geocaching. Actually, quite a lot of the cachepages have co-ordinates which were measured with non-WAAS GPSrs, so WAAS in those cases isn't much of an improvement in your chances of going directly to the hide with sole reference to the GPS.

 

Cheers, The Forester

"techie", I suppose

[+Skippy and Pingu]

Thanks for the explaination. As you say, probably doesn't help much for geocaching, we've managed 170 finds without it.

[nicowlala]

Ok, I'm joining this conversation a bit late on but I have a question. I have a fair idea how WAAS works but have not yet managed to get a lock on one - probably because i've been too impatient.

My question is - does the accuracy only improve when you are actually locked onto a satalite or does it remain after you turn GPS off and on again the next time you use it? (without re-locking)

[+The Forester]

does the accuracy only improve when you are actually locked onto a satalite or does it remain after you turn GPS off and on again the next time you use it? (without re-locking)

Yes: and No: in that order.

 

WAAS data needs to be fresh. It delivers corrections of errors which are constantly changing. The satellite controllers take out the errors which are predictable in the long term. For example, they have a model of the actual performance of each atomic clock in each satellite and they regularly apply calibration adjustments to eliminate the known drift rates. They also take out the predictable anomalies in the satellites orbit which are caused by the unevenness of the Earth's gravity field.

 

What WAAS (or any other Differential service) does is to give you almost real-time corrections.

 

Age of Correction is an issue in all Differential systems. It's no good knowing what the errors were yesterday when you are using the GPS today.

 

Of course there is always some delay in getting the information. After all, the WAAS transmits corrections for scores of areas or 'tiles' within the coverage area and that list of correctiosn necessaroly take some time to broadcast. Foir that reason, it also transmits the rate of drift of the corrections and the rate of change and the rate of change of the rate of change. With this metadata the differential system in your GPSr can make a bit of guess as to what the corrections will be x seconds after the corrections were computed. This can only be extrapolated for so long before the forecast becomes meaningless. A few seconds is OK, even a few minutes, but an hour or two would be much too long and the correction data would be completely worthless for realtime position fixing.

 

This problem showed itself in the earliest version of at least one well known brand of GPSr. They allowed the thing to go on using old WAAS data for up to 50 minutes after the correction signal was lost. The applied results were complete gibberish and became the root cause of the still ongoing urban legend that WAAS reduces rather than enhances accuracy in retail level GPSrs.

[+Birders]

Silly question I know... but presumably the GPSr has to have WAAS in its programme to start with. Our old GPS12XL presumably will not have satellite 33 in its memory... or will it show up anyway if it sees it (but presumably still can't use it). We've never seen that sat yet..

[+The Forester]

Yes. The GPSr must be a model which is designed for WAAS. Most of the older style units were designed before WAAS had been devised and so cannot receive the WAAS signals or use them to improve fix quality.

 

A few of the intermediate age models were given hardware which is WAAS-ready, but needed a firmware update to actually implement WAAS.

 

As ever, consult the manual and/or the manufacturer's website for detailed info specific to any individual model/version.

[+Birders]

Many thanks to The Forester - good info as usual. Soon time to dig out that Barclaycard we guess!!

[nicowlala]

Wow, Mr Forester, you know your stuff!!

Many thanks for the info.

Next time i'm out caching I'll give the WAAS a go, esp when I get around to placing my next hidden cache.

[+xby]

I saw my GPSr go into 'Diffeerntial' mode for the first time while in Canada earlier this year. That was available every time I used the set.

 

The next time was just a few weeks ago at home when my set went 'Differential' while out walking. But the next day - nothing - just the plain old 5/6/7 metre accuracy.

 

Then yesterday, while in Denmark, 'Differential' again. Oddly this time the reported accuracy varied from a best of 2 metres to sometimes only 7 metres despite being able to see almost a whole sky and the sats being pretty evenly distributed.

 

I did a bit of Googling when I first saw the 'Differential' display on my set and found all sorts of (sometimes conflicting) information. This seemed to suggest that the WAAS service for Europe is being tested and will be on 'soon', and that the 'differential' information is boradcast from a geostationary sat which is one of the commercial TV broadcast sats.

 

Reading this thread it sounds as though the source of the 'differential' information is known as sat 33 in the GPS constellation.

 

Three questions:

 

a) Is the WAAS service for Europe 'on', 'off', or 'in test'? If not 'on', when is it planned to be switched 'on'?

 

Which satellite is the source of the information for Europe? Is it simply another channel in a commercial TC bird or is it a GPS special? Is this known as GPS sat 33?

 

c) Where is the best, definitive, up to date, source of techy info on GPS and the current state of the service - other than this site of course?

 

My Garmin V set seems to simply detect WAAS is available and use it - I do not have to do anything, and I have not noticed any loss of channels when the service is not around.

[+The Forester]

a) Is the WAAS service for Europe 'on', 'off', or 'in test'? If not 'on', when is it planned to be switched 'on'?

 

It is both 'on' and 'in test'. It is (usually!) available throughout Britain 24x7.

 

Which satellite is the source of the information for Europe?

In the UK it is InMarSat's Atlantic Ocean Region East (AOR-E) which is best received. It's about 25° to 30° above the horizon, depending where in the UK you are.

 

Is it simply another channel in a commercial TC bird or is it a GPS special?

Yes, no. There is a GPS special, called Artemis, but it had a major setback when an upper stage booster rocket failed during launch. By some very clever manoeuvring the engineers have nursed it into a useable orbit, but the delay has cost a couple of years.

 

Is this known as GPS sat 33?

Yes. It is actually PRN120, but Garmin calls it #33.

The Indian Ocean - West satellite is #39. Artemis is #37.

 

Where is the best, definitive, up to date, source of techy info on GPS and the current state of the service

That's a qualitative judgement.

 

Perhaps one of the best is the one run by the people who run the GPS itself .

 

Cheers, The Forester

[+xby]

Many thanks for your excellent, and incredibly fast, answers.

 

I am fascinated that the service is now 24x7. I rarely see my GPSr 'grab' the service, and over the past few weeks I have been watching to see if there is a pattern. Now I know a bit more about it I shall look for sats 33 and up, and check if the relevant part of the sky is visible.

[+wildlifewriter]

My Garmin V set seems to simply detect WAAS is available and use it - I do not have to do anything, and I have not noticed any loss of channels when the service is not around.

That is correct. There is ONE thing you might do, though...

 

The Garmin GPS V is an excellent unit, but it's been around for a while. During that period, several firmware revisions have been brought out - and the most recent ones directly affect the use of WAAS/EGNOS

 

The current firmware revsion is 2.50. I suggest that you check which version your unit has (read the manual, p56) and upgrade it if necessary.

 

-Wlw.

[+sTeamTraen]

Actually, quite a lot of the cachepages have co-ordinates which were measured with non-WAAS GPSrs, so WAAS in those cases isn't much of an improvement in your chances of going directly to the hide with sole reference to the GPS.

I imagine it's the vast majority of them, at least outside North America... but I would have thought that, statistically, it's got to help a bit. If the original coordinates were 6m off and my GPSr can be 6m off, then on average (I think this is right, A-level Maths was a long time ago) the total error will be 8.4m (6(sqrt(2)). If my error can be reduced to 3m then the average error goes down to something like 6.7m (help, doing square roots in my head here). Not spectacular, but nice to have.

 

Or is this all rubbish ?

[+Woody's Wanderers]

Tried caching with WAAS on today. Did notice a series of D's on the screen (now I know what they are, thanks!) Didn't notice a great difference in accuracy but did notice that the GPS kept it's signal better (this was after we'd done Sleepy!)

 

Does WAAS make keeping a 'lock' on satellite signals easier, despite, say, tree cover?

Edited October 16, 2005 by Woody's Wanderers

[+Team Hydro]

No, receiving WAAS or not will not affect the "lockability" of the GPSr onto the usual satellite signals.........

[+wildlifewriter]

Does WAAS make keeping a 'lock' on satellite signals easier, despite, say, tree cover?

No. It has nothing to do with that.

 

-Wlw.

[+Woody's Wanderers]

Righto! thanks.

[+Thrak]

I've tried enabling WAAS on my 76CS and I normally don't get a signal for those satellites. When I tried it in Montana it worked and it worked way up high on a hilltop in Idaho but, here in my home town of Chico, California I generally can't get a lock on those satellites. If I'm doing a cache way up on the rim of the canyon in the local park I can get the signal but in town I just don't see those satellites. There are a lot of trees in my town so maybe that is the problem. Not sure but WAAS doesn't seem to be useful here for me.