[goose157]

Hi all
I am very new to this fantastic hobby!
I have a question regarding WAAS - My foretrex 301 has this function but what does it actually do here in the uk?
I have swtiched it on and off and there does not seem to be any benefit to the accuracy of my gps. Is WAAS actually usable in the uk,
if so is my foretrex faulty, as i see no difference or, is it that my location Derbyshire UK that is not in range??
Cheers

Chris Scott (Goose157)
DerbyShire,
UK.

[Just Roger]

 goose157, on 27 April 2012 - 12:01 AM, said:

Hi all
I am very new to this fantastic hobby!
I have a question regarding WAAS - My foretrex 301 has this function but what does it actually do here in the uk?
I have swtiched it on and off and there does not seem to be any benefit to the accuracy of my gps. Is WAAS actually usable in the uk,
if so is my foretrex faulty, as i see no difference or, is it that my location Derbyshire UK that is not in range??
Cheers

Chris Scott (Goose157)
DerbyShire,
UK.

Hi there, WAAS is actually the American system, the European equivalent is EGNOS (European Geostationary Navigation O??? (Orbiting?) System.

Amazingly, even astoundingly) the two systems are compatible so if you switch on WAAS on your GPSr it will pick up the EGNOS satellites. As these satellites are in Geostationary orbit they are over the equator and so are not far above the horizon and may be difficult to pick up in the north of England and Scotland
(Thats why a bigger Sky dish is needed in Scotland). I don't know about your Fortrex but most Garmins show a 'D' in the signal strength bars in the Satellite page when you are locked on to EGNOS.

As to what it does for you, until you get the 'D' to indicate that the system is in use the answer is - not a lot. Once it is all locked on and running the "accuracy * " figure may drop from around 20 feet to six or seven.

* Not wishing to start a flame war - the figure which Garmin and others choose to call accuracy is really nothing of the sort. It is purely a theoretical calculation based on the distribution of the satellites at the time (If they are all in a straight line the "accuracy" will be terrible compared to the case when the satellites are nicely spread around over the sky). It takes no account of other factors such as cloud cover reflections off buildings , trees or other local factors. Also, I believe it is a Standard Deviation figure so the 95% confidence level will be 3 times the displayed figure even ignoring local interferences.

[goose157]

 Just Roger, on 27 April 2012 - 12:25 AM, said:

 goose157, on 27 April 2012 - 12:01 AM, said:

Hi all
I am very new to this fantastic hobby!
I have a question regarding WAAS - My foretrex 301 has this function but what does it actually do here in the uk?
I have swtiched it on and off and there does not seem to be any benefit to the accuracy of my gps. Is WAAS actually usable in the uk,
if so is my foretrex faulty, as i see no difference or, is it that my location Derbyshire UK that is not in range??
Cheers

Chris Scott (Goose157)
DerbyShire,
UK.

Hi there, WAAS is actually the American system, the European equivalent is EGNOS (European Geostationary Navigation O??? (Orbiting?) System.

Amazingly, even astoundingly) the two systems are compatible so if you switch on WAAS on your GPSr it will pick up the EGNOS satellites. As these satellites are in Geostationary orbit they are over the equator and so are not far above the horizon and may be difficult to pick up in the north of England and Scotland
(Thats why a bigger Sky dish is needed in Scotland). I don't know about your Fortrex but most Garmins show a 'D' in the signal strength bars in the Satellite page when you are locked on to EGNOS.

As to what it does for you, until you get the 'D' to indicate that the system is in use the answer is - not a lot. Once it is all locked on and running the "accuracy * " figure may drop from around 20 feet to six or seven.

* Not wishing to start a flame war - the figure which Garmin and others choose to call accuracy is really nothing of the sort. It is purely a theoretical calculation based on the distribution of the satellites at the time (If they are all in a straight line the "accuracy" will be terrible compared to the case when the satellites are nicely spread around over the sky). It takes no account of other factors such as cloud cover reflections off buildings , trees or other local factors. Also, I believe it is a Standard Deviation figure so the 95% confidence level will be 3 times the displayed figure even ignoring local interferences.

Thank you so much for your lightening fast reply!!
I have been scratching my head about this one for a week or two...
I have as i write turned Waas/Egnos!! back on and put the gps in the open to see if i can get some 'D's in the sat screen...
Thanks again very much appreciated info.
Chris Scott,
Derbyshire,
UK.

[The Patrician]

WAAS / EGNOS was designed for the use of aircraft and shipping to make precise approaches even when visibility was bad. You will note that both of these applications have an unimpeded clear view of the sky!

There are, if my memory serves correctly, rare occurences when the use of WAAS degrades the signal and gives a worse positon than you are getting from the normal satellites.

We've had this discussion here before and I seemed to be in a minority of one because I leave it turned off. With all the possible errors in searching for Tupperware in a hedge I reckon the use or otherwise of WAAS is the least of your worries!

http://www.gpsreview.net/waas/

[Amberel]

 goose157, on 27 April 2012 - 12:48 AM, said:

I have as i write turned Waas/Egnos!! back on and put the gps in the open to see if i can get some 'D's in the sat screen...
Thanks again very much appreciated info.

Just Roger's reply is very good. Just to emphasize, when you put your GPS outside, put it somewhere there is an unimpeded view quite low to the south.

You might find the EGNOS satellite is shown as #33 in your display. It may take a little while to download all the information, but the good news is that the improvements may remain for a while even after you lose the EGNOS signal.

Re. the Patician's point that it is possible for the position using EGNOS to be less accurate than when not using it. This is only true if you take a very strange view of GPS accuracy. In exactly the same way it is possible to get a worse position using 12 satellites than it is using just 3. But both using more satellites, and using EGNOS, will result in an overall improvement in accuracy, and there is no logical reason not to use EGNOS if it is available.

The accuracy figure reported by most Garmins is a 50% CEP figure. That means the unit estimates that your actual position will be within the stated figure for half the time. This is a horrible way to present an accuracy indication because it is so easily misundersood.

Rgds, Andy

[Matthew 7:7 Too]

I live in Staffordshire and find that my Garmin Orgeon will occasionally use the EGNOS/WAAS digital correction satellite, but only in situations where I have a clear view of the southern horizon (like up in the Roaches etc!)

On the other hand, when I was caching on the south coast of Britany last year it was coming in straight away!

Chris

[sussamb]

 The Patrician, on 27 April 2012 - 12:57 AM, said:

We've had this discussion here before and I seemed to be in a minority of one because I leave it turned off. With all the possible errors in searching for Tupperware in a hedge I reckon the use or otherwise of WAAS is the least of your worries!

No you're not, there are at least 2 of us, I leave mine turned off too. When I got my first GPS, an Etrex Legend H, I did some quite extensive trials in the Isle of Wight, where the WAAS/EGNOS signal is easily seen. While the device indicated a better accuracy I saw no difference in actual use, so I've never bothered since

I now have an Etrex 20. With GPS and GLONASS switched on I find the accuracy is even better than my old Etrex, and I can't see any point therefore in using WAAS/EGNOS.

[Amberel]

 sussamb, on 27 April 2012 - 04:35 AM, said:

... I can't see any point therefore in using WAAS/EGNOS.

Does that mean you can see a point in NOT using it? If so I'd be interested to understand what that is?

Using WAAS/EGNOS is a "may win, won't lose" situation.

Rgds, Andy

[sussamb]

As I posted, it made no difference in the real world ...

It's just more processing therefore that *could* go wrong, so I can't see the point.

[The Patrician]

There are some cons with WAAS(/EGNOS):

You're using a channel on your GPS for this. If you can't see the WAAS satellite, quite likely in urban, forested or hilly country, that's one less ordinary satellite that you can see.

It will use batteries faster, there's considerably more processing to be done using the WAAS signal. AFAIK no GPS will lock onto WAAS in power saving mode. I suspect there are many other settings on a GPS which will use batteries faster than using WAAS, backlighting for example, but your batteries will be used faster.

What do you need this perceived extra accuracy for? Your GPS is already more accurate than any map you're likely to own. Many caches are set by people using smartphones, I don't know of any that use WAAS so the improved accuracy of WAAS on your receiver is not going to get you any closer to them.

If I was flying an aircraft I'd turn it on, for hillwalking, driving and geocaching I don't think it's worth the battery drain.

Others may have different and perfectly valid views, frankly I can't get worked up over it, it's a personal choice that makes little difference in the real world.

[Amberel]

 sussamb, on 27 April 2012 - 10:02 AM, said:

As I posted, it made no difference in the real world ...

It's just more processing therefore that *could* go wrong, so I can't see the point.

Ah, but that is approximately 50% the point of WAAS/EGNOS - it actually makes LESS to go wrong.

WAAS/EGNOS gives you 2 significant advantages. One is the ionospheric map, which helps to improve accuracy by allowing the receiver to factor in ionospheric signal distortion. The second thing is that it monitors the health of the satellites and warns your receiver not to use any that are transmitting poor quality data - and that does happen. If no satellites are transmitting bad data there won't be any improvement due to this function, but if any are bad, then there will. Whether it's noticeable or not also depends on the observer.

Rgds, Andy

[Amberel]

 The Patrician, on 27 April 2012 - 11:01 AM, said:

You're using a channel on your GPS for this. If you can't see the WAAS satellite, quite likely in urban, forested or hilly country, that's one less ordinary satellite that you can see.

But most devices these days have minimum 12 channels. Given that 4 satellites give you a 3D solution, 11 satellites means you have a massively over-determined solution. The difference between a 12 channel over-determined solution and an 11 channel overdetermined solution would be VERY hard to detect - FAR harder than detecting the difference between EGNOS/no EGNOS.

 The Patrician, on 27 April 2012 - 11:01 AM, said:

Many caches are set by people using smartphones, I don't know of any that use WAAS so the improved accuracy of WAAS on your receiver is not going to get you any closer to them.

The error when looking for a cache is the vector sum of the errors for the setter and the searcher. If you do the maths you will find there is something to be gained even if WAAS/EGNOS is used on only one of those devices.

 The Patrician, on 27 April 2012 - 11:01 AM, said:

I can't get worked up over it ...

I think you will find that none of us are actually getting worked up over it .

Rgds, Andy

[sussamb]

Oh I dunno ... one of us on here is and seems desperate to convince at least 2 of us that WAAS/EGNOS is worthwhile having, when clearly neither of us has seen any real world benefit.

Me, I'll stick with it off ... happy that others keep it on if they so wish

This post has been edited by sussamb: 28 April 2012 - 01:11 AM

[The Patrician]

 sussamb, on 28 April 2012 - 01:10 AM, said:

Me, I'll stick with it off ... happy that others keep it on if they so wish

Shall we form a club?

[Amberel]

 sussamb, on 28 April 2012 - 01:10 AM, said:

Oh I dunno ... one of us on here is (getting worked up over it) and seems desperate to convince at least 2 of us that WAAS/EGNOS is worthwhile having ...

I know you delight in taking every opportunity you can to snipe at me, but all I'm doing is explaining to you that it DOES improve accuracy (and reliability), even though you haven't noticed it. I'm not trying to persuade you to use it, just trying to understand why you don't (which you still haven't explained logically).

Depending on the circumstances at the time the improvement may be very small or it may be quite large, but it does exist.

Rgds, Andy

[The Patrician]

Oh, bugrit! I don't think either of us are going to get one of Andy's 'Top Cache' Awards now.

(Not that it was likely in my case anyway!)

[sussamb]

Not wanting to snipe at anyone

As I did explain, it's more processing that could go wrong and having never seen any real world advantage I don't see the point in taking the risk. Why 'turn something on' when it's of no real benefit?

Additionally, have a read of this article http://www.kowoma.de.../waas_egnos.htm

and in particular this section:

But since most manufacturers recommend switching WAAS/EGNOS off if not within the area where the signals are provided for, it may be assumed that the receivers do not make full use of all information provided and do not check whether the correction should be used or not. That way, the position may be even worse when WAAS/EGNOS is switched on when no proper correction signal is provided.

Given that in the UK reception is pretty ropey I'll keep mine off thanks.

I won't comment anymore in case I get accused of sniping again. I'm happy with my choice, I'm sure you're happy with yours. Let's just agree to disagree shall we?

[sussamb]

 The Patrician, on 28 April 2012 - 02:57 AM, said:

Oh, bugrit! I don't think either of us are going to get one of Andy's 'Top Cache' Awards now.

(Not that it was likely in my case anyway!)

Guess you're right, but I'm happy as I am

[Amberel]

 The Patrician, on 28 April 2012 - 02:57 AM, said:

Oh, bugrit! I don't think either of us are going to get one of Andy's 'Top Cache' Awards now.

I do understand that was said tongue in cheek, but I want to clarify that it absolutely is not so . The awards are for the cache, and any difference of opinion I have with anyone has not the slightest effect on how I rate their caches.

 The Patrician, on 28 April 2012 - 02:57 AM, said:

(Not that it was likely in my case anyway!)

Then I challenge you set a top quality cache . It looks like you're not local to me, but in a lovely part of the country, and I do travel for good caches .

Rgds, Andy

[Amberel]

 sussamb, on 28 April 2012 - 02:58 AM, said:

Additionally, have a read of this article http://www.kowoma.de.../waas_egnos.htm

and in particular this section:

But since most manufacturers recommend switching WAAS/EGNOS off if not within the area where the signals are provided for, it may be assumed that the receivers do not make full use of all information provided and do not check whether the correction should be used or not. That way, the position may be even worse when WAAS/EGNOS is switched on when no proper correction signal is provided.

Errm, did you see the bit where he said "it may be assumed"? He doesn't actually know. As an assumption it is questionable. And in my user manual and on the WAAS page on their web site, Garmin do NOT recommend it is switched off!

 sussamb, on 28 April 2012 - 02:58 AM, said:

Let's just agree to disagree shall we?

Entirely depends on what you are asking to "agree to disagree" on. If it is that you are free to choose, then there never was any disgreement in the first place! And I can agree that you have never noticed an improvement. But I can't agree that there isn't an improvement.

Rgds, Andy

[sussamb]

Ermmm, yes I did see it but seeing as you appear to make lots of assumptions I felt it worthwhile to point it out

We're going around in circles here and I think you're missing the point. In the real world, as opposed to any assumtions you wish to make, having WAAS/EGNOS selected in the UK *appears* to make no difference, believe me I spent 2 days doing tests in the Isle of Wight last summer where at least you can get an EGNOS signal. Not an assumption, a fact.

Since there is no discernible difference I see no point in having it switched on, since it's taking processor power that I'd rather was doing something else, eg being free to scroll the map faster.

I use my Etrex 20 with GPS and GLONASS, mainly for walking but I also geocache with it. It regularly puts me within a few metres of caches ... and has never got me lost while out walking.

I'm happy with that, unless you tell me that with WAAS/EGNOS on it'll take me exactly to the cache, but then that would make caching really boring, wouldn't it?

This post has been edited by sussamb: 28 April 2012 - 05:31 AM

[Amberel]

 sussamb, on 28 April 2012 - 05:30 AM, said:

Ermmm, yes I did see it but seeing as you appear to make lots of assumptions I felt it worthwhile to point it out

No assumptions made by me, if you think there were then please point them out, and also why you might think they are invalid.

The only way that there would not be an improvement would be if there was a bug in the WAAS/EGNOS implementation in a specific device, and I have no reason to suppose that is the case for the eTrex 20.

I do, of course, agree that GPSrs are mostly of adequate performance for caching purposes without the use of WAAS/EGNOS. And that for our purpose the improvement is, for MOST (but not ALL) of the time, small enough not to be a significant consideration. And also that, other than on moorland or other open country, use in the UK is restricted due to the elevation of the satellites. But then I've never suggested otherwise.

Rgds, Andy