Do you use WAAS/EGNOS?

[BFG99]

Many of the handheld GPSs out there have the option to turn WAAS (or for Europe, EGNOS) on or off. Out of curiosity, do you use it? Why or why not? Under what circumstances?

 

To be honest, I haven't seen a huge improvement in accuracy when I enable WAAS on my Garmin eTrex Vista HCx, but consistency goes up a bit (i.e. it doesn't drift quite as much). I'm not sure if it's worth using, especially if it causes additional battery drain.

 

That also brings me to two other questions:

(1) Yesterday, my unit tried to simultaneously lock onto GPS #13 and WAAS #13. Oddly, it couldn't seem to hold a lock on either one, and often when it did lock onto one it immediately lost the lock on the other. The other 10 satellites held their locks. Does anyone know if this is a bug?

(2) If I'm using WAAS and the person who placed the cache wasn't when they recorded the coordinates, am I actually at a disadvantage versus turning WAAS off?

[yogazoo]

Many of the handheld GPSs out there have the option to turn WAAS (or for Europe, EGNOS) on or off. Out of curiosity, do you use it? Why or why not? Under what circumstances?

 

(2) If I'm using WAAS and the person who placed the cache wasn't when they recorded the coordinates, am I actually at a disadvantage versus turning WAAS off?

 

I always have WAAS enabled. The miniscule battery drain WAAS incurs is negligible. Just use it. If the WAAS corrections don't apply to you at your location then the GPS unit will figure that out for you.

 

You may sopmetimes have odd behavior when it comes to those satellites. If it's bothering you just power cycle your unit. That usually clears up any odd behavior on the GPS unit end.

 

If the person placing the cache was using a paper map with a UTM coordinate stencil grid are you actually at a disadvantage using a GPS unit? No, achieving greater accuracy never places you at a disadvantage. The equation here is (Hiders Error) + (Finders Error) = (Actual Distance from Cache). If your error goes down, regardless of the hiders error, than your closer to the cache period.

Edited June 22, 2014 by yogazoo

[BFG99]

Heh, good point yogazoo. I suppose that the only time WAAS might put a person at a disadvantage is if turning it off would cause exactly the same error as what the hider found. There are too many variables involved to be able to rely on that consistently.

 

Since it doesn't seem to hurt anything, other than the small additional battery drain, I'll probably keep it on. That inability to lock onto both 13's was odd though, and I'll keep an eye on the unit to see if something like that happens again.

[+user13371]

{deleted bad joke that nobody got}

Edited June 22, 2014 by user13371

[+andyakashrek]

For what it's worth I cache in Gloucestershire and have a vista hcx and a 550t. The hcx with waas enabled consistently places me nearer the cache than the 550t with waas. However disable waas on the 550t and the accuracy improves a lot and is the same as the hcx. Maybe a firmware issue?

[yogazoo]

For what it's worth I cache in Gloucestershire and have a vista hcx and a 550t. The hcx with waas enabled consistently places me nearer the cache than the 550t with waas. However disable waas on the 550t and the accuracy improves a lot and is the same as the hcx. Maybe a firmware issue?

 

If by "accuracy" you mean the "EPE" data it might be deceiving you. "EPE" readings don't really mean a thing and might be more true with WAAS enabled. WAAS/EGNOS measures atmospheric distortion and attempts to correct it. If you do see higher EPE numbers with WAAS enabled the EPE may in fact be more representative of the true expected error. With WAAS off the only statistics the GPS has to calculate EPE are satellite number and arraignment. You have to be careful using EPE as a true measurement of accuracy because it's all relative to available data and the algorithm Garmin decides to use (which may be different between units).

 

In short, be very careful about making statements like "more accurate" when referencing the EPE numbers. Even if you're using anecdotal observations about being "closer to the cache" you have to be careful about drawing any kind of factual conclusions about accuracy. If WAAS /EGNOS provides the GPS unit with more information about the satellite signals it receives (and it does) then I will trust that more information is a good thing most if not all of the time. To me the additional information is worth the extra 0.5 ma the unit draws with it enabled.

 

And hey, the HCX is such a dinosaur if they haven't gotten the firmware fixed by now they never will.

Edited June 22, 2014 by yogazoo

[+andyakashrek]

For what it's worth I cache in Gloucestershire and have a vista hcx and a 550t. The hcx with waas enabled consistently places me nearer the cache than the 550t with waas. However disable waas on the 550t and the accuracy improves a lot and is the same as the hcx. Maybe a firmware issue?

 

If by "accuracy" you mean the "EPE" data it might be deceiving you. "EPE" readings don't really mean a thing and might be more true with WAAS enabled. WAAS/EGNOS measures atmospheric distortion and attempts to correct it. If you do see higher EPE numbers with WAAS enabled the EPE may in fact be more representative of the true expected error. With WAAS off the only statistics the GPS has to calculate EPE are satellite number and arraignment. You have to be careful using EPE as a true measurement of accuracy because it's all relative to available data and the algorithm Garmin decides to use (which may be different between units).

 

In short, be very careful about making statements like "more accurate" when referencing the EPE numbers. Even if you're using anecdotal observations about being "closer to the cache" you have to be careful about drawing any kind of factual conclusions about accuracy. If WAAS /EGNOS provides the GPS unit with more information about the satellite signals it receives (and it does) then I will trust that more information is a good thing most if not all of the time. To me the additional information is worth the extra 0.5 ma the unit draws with it enabled.

 

And hey, the HCX is such a dinosaur if they haven't gotten the firmware fixed by now they never will.

Perhaps you misunderstood what I wrote.

I loaded the same cache information on both units and went out to look for them, hcx in one hand 550t in the other, both waas enabled. The hcx consistently pointed to the cache hiding place and reported that there was only a few feet left to travel,compass page. Whilst stood in the same position the 550t would point in a different direction and often between 20 - 30 feet left to travel. This behaviour carried on for each cache i looked for. However with waas disabled on the 550t it behaved the same as the hcx with waas. That is it pointed to the same place and the same distance to travel.

That is why I said the hcx with waas was 'more accurate ' than the 550t with waas. The hcx consistently put me nearer to the cache hiding place. With the 550t and waas I could have been looking more than 30 feet away and in a different direction, based on compass screen.

As for firmware I was referring to the 550t firmware. I acquired the unit with v3.9, updated to present version 6.6 and found compass behaviour was erratic, sticky and sometimes froze. Did a bit of research and found that this was common with that version. Downgraded several versions to 5.50 and that sorted it. So it looks like garmin still have work to do with this unit whereas the hcx dinosaur seems to function properly.

[jholly]

For what it's worth I cache in Gloucestershire and have a vista hcx and a 550t. The hcx with waas enabled consistently places me nearer the cache than the 550t with waas. However disable waas on the 550t and the accuracy improves a lot and is the same as the hcx. Maybe a firmware issue?

 

If by "accuracy" you mean the "EPE" data it might be deceiving you. "EPE" readings don't really mean a thing and might be more true with WAAS enabled. WAAS/EGNOS measures atmospheric distortion and attempts to correct it. If you do see higher EPE numbers with WAAS enabled the EPE may in fact be more representative of the true expected error. With WAAS off the only statistics the GPS has to calculate EPE are satellite number and arraignment. You have to be careful using EPE as a true measurement of accuracy because it's all relative to available data and the algorithm Garmin decides to use (which may be different between units).

 

In short, be very careful about making statements like "more accurate" when referencing the EPE numbers. Even if you're using anecdotal observations about being "closer to the cache" you have to be careful about drawing any kind of factual conclusions about accuracy. If WAAS /EGNOS provides the GPS unit with more information about the satellite signals it receives (and it does) then I will trust that more information is a good thing most if not all of the time. To me the additional information is worth the extra 0.5 ma the unit draws with it enabled.

 

And hey, the HCX is such a dinosaur if they haven't gotten the firmware fixed by now they never will.

Perhaps you misunderstood what I wrote.

I loaded the same cache information on both units and went out to look for them, hcx in one hand 550t in the other, both waas enabled. The hcx consistently pointed to the cache hiding place and reported that there was only a few feet left to travel,compass page. Whilst stood in the same position the 550t would point in a different direction and often between 20 - 30 feet left to travel. This behaviour carried on for each cache i looked for. However with waas disabled on the 550t it behaved the same as the hcx with waas. That is it pointed to the same place and the same distance to travel.

That is why I said the hcx with waas was 'more accurate ' than the 550t with waas. The hcx consistently put me nearer to the cache hiding place. With the 550t and waas I could have been looking more than 30 feet away and in a different direction, based on compass screen.

As for firmware I was referring to the 550t firmware. I acquired the unit with v3.9, updated to present version 6.6 and found compass behaviour was erratic, sticky and sometimes froze. Did a bit of research and found that this was common with that version. Downgraded several versions to 5.50 and that sorted it. So it looks like garmin still have work to do with this unit whereas the hcx dinosaur seems to function properly.

Did both show a WAAS lock? You might have WAAS turned on but unless the units indicate they have a WAAS lock they are not using WAAS.

[BFG99]

That's very interesting behaviour (intentional British English spelling for the European!) I too would question if they both had a WAAS lock, and were using the same GPS satellites. If so, then perhaps the 550t uses a different algorithm to handle multipathing and drift when WAAS is on, versus when it is off? How curious.

[+andyakashrek]

I didn't check to see if waas lock had been achieved, I will place them both side by side in the garden this afternoon and see what happens and what satellites are being picked up. Went out last night and just used the 550t, waas disabled, and found the 4 caches I went for easily with the unit indicating where gz should be and in all 4 cases the cache was within a couple of feet of indicated position, even under heavy tree cover.

[+BAMBOOZLE]

The units we currently use most are the 62S and I always have WAAS enabled. I don't know if they would be more accurate getting to GZ with WAAS off but most of the time on arriving at GZ I hit my head on the cache.

[+andyakashrek]

Ok, sat in garden this afternoon and placed both units on the deck and powered both on at the same time. The hcx got more bars full much quicker than the OR. After about 10 mins the hcx had D showing on most satellites. The OR took nearly 25 mins to reach D state. BUT, the hcx saw and locked onto more satellites. The OR seemed to have trouble finding and holding onto the lower number satellites but in the higher range was the same. It also found #37, which the hcx did not, but with no D, and strangely tried to connect with #49.

When the OR found and locked onto #2,#10,#12 the indicated accuracy was nearly the same as the hcx, @11 ft, however when it dropped these 3 satellites indicated accuracy went out to @30 feet. The hcx did not drop any and remained steady.

This drifting may go some way to explain the inaccuracies I experienced in the field in side by side tests.

This dropping behaviour carried on for the 45 mins I observed the satellite map. The units were not touched or moved during the test. At any time the hcx showed more D's than the OR.

Any thoughts?

[+andyakashrek]

I was more interested in why the OR dropped the lower numbered satellites. Do they used different chip sets?

[+fizzymagic]

For those interested http://www.gpsreview.net/waas/ and https://sites.google.com/site/gnssgofor/gnss

 

GLONASS is far more useful than WAAS/EGNOS IMO, and certainly tests I've done show no real improvement with WAAS/EGNOS on, even when (and not often) a WAAS/EGNOS signal is being received.

 

GLONASS and WAAS/EGNOS serve two entirely different purposes. Your claim that you don't get "good" EGNOS signal in England basically just illustrates that you don't know what you are talking about.

[+fizzymagic]

I know exactly what I'm talking about, and the difference between WAAS/EGNOS and GLONASS. I did a fair bit of testing a while back and when you do get a good EGNOS lock in the UK the actual difference in accuracy (rather than simply the reported accuracy on the GPS) was negligible, whereas enabling GLONASS does show a discernible difference in accuracy and the ability to hold a good satellite lock.

 

I seriously doubt that you actually measured accuracy with and without EGNOS, but if the difference in accuracy was that low then you either did it at night or the EGNOS system is terrible. Here in the USA the difference with and without WAAS is quite significant.

 

Of course the addition of GLONASS will have your device report a better accuracy (there is lower HDOP), and of course it gives you a better satellite lock. There is no reason not to use it. But it is susceptible to exactly the same errors as GPS, which WAAS/EGNOS were designed to correct.

 

Your insistence that EGNOS/WAAS and GLONASS can be compared and that one is "preferable" to the other is, as I said before, nonsensical and evidence of profound ignorance. They are different things entirely.

 

As for an EGNOS lock in the UK, you may wish to cross the pond and give it a try, you'll then find out what I mean

 

I've done it and verified that it worked perfectly with my GPS, thank you very much. From a number of locations in the UK. Why is it that you think it doesn't work well? Are you one of those people who think you can't see GEO satellites from England?

[+andyakashrek]

To get back to the OP's questions I would say YES I use waas on my vista hcx and NO I don't use waas on my Oregon 550t.

Edited June 26, 2014 by andyakashrek

[+Team CowboyPapa]

I can understand why actual, real quantitative data supporting one's qualitative conjectures is not posted herein. I did exactly that, posted quantitative data from testing (a significantly sized data set for statistical determinations, I might add) and was seriously excoriated for performing pseudo-science as noted here in post #41.

 

Yes, in the future, fingers that type real, quantitative test data shall never brush mine.

[+Team CowboyPapa]

Perfect, and I do agree that WAAS and GLONASS are sufficiently different as to preclude functional comparisons.

Edited June 26, 2014 by Team CowboyPapa

[39_Steps]

I also have a cowboy anecdote regarding gps accuracy, but of a slightly different nature. I was driving westbound on a California (USA) multi-lane freeway in an area where many of the old cowboy western movies were once filmed. From time to time I glanced at the tracking on a Delorme PN-40 gps device. The device was not programmed to snap the display to the road or to a route.

 

I was in the right hand (slow in the USA) lane next to the shoulder heading westbound as mentioned above, and the device seemed to be tracking the highway perfectly. Suddenly the track started veering to the south clear across all the lanes of the divided highway and then perhaps another 30 feet (10 meters) into the brush on the other side of the road. Just as quickly the track returned to its proper place in my westbound lane.

 

What had happened, I wondered. Then I looked in the rear view mirror. Oh yeah, I had not even noticed that the highway had been cut through the slope of one of those old cowboy movie mountains so that we could all drive in a straight line. The satellite geometry at that point in time was such that said mountain caused major interference if only for a few seconds.

 

Please, those of you who post data, please also post the location of various trees, canyons, and buildings potentially blocking satellites - even if it is only your own two story house shading your own back yard.

[BFG99]

One small clarification on the above posts - for those who are wondering, any satellites above 32 are WAAS/EGNOS satellites, though there are a few below 32 as well. If I remember correctly there are around 10 WAAS/EGNOS satellites altogether; 13, 37 and 49 show up most frequently for me in the central US.

 

On a typical Garmin, the last 2 satellite positions (out of 12) are reserved for WAAS/EGNOS satellites when WAAS/EGNOS is turned on. Interestingly, this means it's only possible to lock onto 10 GPS satellites when WAAS/EGNOS is turned on, but 12 when it's turned off.

Edited June 27, 2014 by BFG99

[+BAMBOOZLE]

One small clarification on the above posts - for those who are wondering, any satellites above 32 are WAAS/EGNOS satellites, though there are a few below 32 as well. If I remember correctly there are around 10 WAAS/EGNOS satellites altogether; 13, 37 and 49 show up most frequently for me in the central US.

 

On a typical Garmin, the last 2 satellite positions (out of 12) are reserved for WAAS/EGNOS satellites when WAAS/EGNOS is turned on. Interestingly, this means it's only possible to lock onto 10 GPS satellites when WAAS/EGNOS is turned on, but 12 when it's turned off.

 

Thats the first clear explanation I've read which explains how accuracy is increased by turning off WAAS ( assuming WAAS is poor )...I think WAAS works well in Louisiana and I usually have the " little D's " on the satellite bars.

[yogazoo]

On a typical Garmin, the last 2 satellite positions (out of 12) are reserved for WAAS/EGNOS satellites when WAAS/EGNOS is turned on. Interestingly, this means it's only possible to lock onto 10 GPS satellites when WAAS/EGNOS is turned on, but 12 when it's turned off.

 

There is also a law of diminishing returns with any number of satellites above the required 4 for a 3D fix. I'm assuming here that it's implied that since WAAS takes up 2 of the 10 channels that somehow 10 channels will provide less accuracy than 12. Sure more sat locks are almost always preferable since it gives you backup data for position calculation and also channels with which to search for new birds. But to say that 10 GPS satellite signals are more accurate than 12 might not be supported under most field conditions since the GPS is probably only using 4-8 of the strongest signals to calculate the position anyway.

Edited June 30, 2014 by yogazoo

[BFG99]

Hmm, I didn't expect the "10 satellites versus 12" thing to be such a big issue. I agree that, if you have even decent signals from 10 GPS satellites, and the satellites aren't all bunched in one small area of the horizon, the extra 2 satellites will not improve accuracy. However, if you have several weak signals, a lot of scattering (due to cloud cover or ground cover), etc., then there's a chance that 12 satellites would be slightly better than 10. But even so...would 12 GPS satellites in that scenario give a greater accuracy than 10 GPS + 2 WAAS? Again, it's difficult to say.

 

In practice, I've found no real improved accuracy from 12 full-strength GPS satellites versus 8. Below 8, the reported accuracy does start diminishing, at least on my eTrex Vista HCx. And the reported accuracy is almost always identical for 12 GPS versus 10 GPS + 2 WAAS.

 

 

Here's a related question - what's the maximum number of satellites that could appear overhead at any one time? Most units can lock onto 12 satellites simultaneously, out of the constellation of 42 (32 GPS + 10? WAAS). How frequently are more than 12 actually available?

[+andyakashrek]

Went out last night and found a cache on top of a high hill with 360 degree view of sky no trees around. 550t did not get a single D in any satellite bar. All full and green highest number #33. Vista hcx mostly D's.

When the OR does get waas lock it is taking 30 mins, more than 5 mins to show position on map page. That's why I'm setting it to normal gps only. Very poor for a high end unit.

[BFG99]

Went out last night and found a cache on top of a high hill with 360 degree view of sky no trees around. 550t did not get a single D in any satellite bar. All full and green highest number #33. Vista hcx mostly D's.

When the OR does get waas lock it is taking 30 mins, more than 5 mins to show position on map page. That's why I'm setting it to normal gps only. Very poor for a high end unit.

#33 would have been a WAAS satellite, since GPS doesn't go above 32. Someone with more knowledge than I please correct me if I'm wrong, but I believe the D only appears if a WAAS satellite is locked on and indicates a differential needs to be used. It's possible that your 550t calculated no differential was needed and so did not display it. Still, it is strange that the Vista did display D's in the same circumstances...maybe it locked onto a WAAS other than 33 which indicated something different?

[+BAMBOOZLE]

Went out last night and found a cache on top of a high hill with 360 degree view of sky no trees around. 550t did not get a single D in any satellite bar. All full and green highest number #33. Vista hcx mostly D's.

When the OR does get waas lock it is taking 30 mins, more than 5 mins to show position on map page. That's why I'm setting it to normal gps only. Very poor for a high end unit.

 

Turned on the units and let them warm up......went out in the front yard ( I live below sea level ).....within seconds my Oregon 450 was reading 12 sats all with the D......after 5-10 min my 62S still had no D's. Sitting back in my den the 450 still has D's ( none on 62)

Went back out with the 62S and after 10 min with sometimes 11 full bars still had no D's......450 in the den still has 11-12 sats w/ D's.

 

Yesterday after a minute or two outside the 62S had 10 sats all with D's.

 

I'm beginning to wonder if there is any rhyme or reason to it.

[BFG99]

If all 12 satellites truly had a "D" on the 450, then the 450 can access more than 12 satellites at once - 12 GPSs and at least 1 WAAS. And I have no way of knowing this for sure, but I suspect whether the "D"s show up or not has to do with which WAAS satellite(s) have been accessed by the unit, and what differential, if any, those satellites suggested.

 

For example, if your 450 connected to WAAS #37, and it provided a differential, that would have been applied to all the GPS satellites. Your 62S, meanwhile, might have connected to WAAS #49 instead, which provided a zero differential. Then the next day it connected to #37.

 

This is all speculative, of course...just trying to figure out the behavior you're seeing based on the small amount of knowledge I have on this. My recommendation--check next time if both units are reporting locks on the same WAAS satellites.

Edited July 2, 2014 by BFG99

[+andyakashrek]

I believe that my two units have different chip sets, I wonder if the software in the OR is not as good as the hcx and that is why it takes so long to get started. I will have a look at what I can find out.

[+fizzymagic]

For example, if your 450 connected to WAAS #37, and it provided a differential, that would have been applied to all the GPS satellites. Your 62S, meanwhile, might have connected to WAAS #49 instead, which provided a zero differential. Then the next day it connected to #37.

 

Why would different WAAS satellites provide different differentials? If they are both truly WAAS, they provide exactly the same information. If one is WAAS and another is EGNOS, then you might see a difference...

[+fizzymagic]

#33 would have been a WAAS satellite, since GPS doesn't go above 32. Someone with more knowledge than I please correct me if I'm wrong, but I believe the D only appears if a WAAS satellite is locked on and indicates a differential needs to be used.

 

That does not make any sense. There is no time that WAAS corrections will not improve the accuracy of your GPS position. At night, the ionosphere corrections are smaller, but they are still there, and the other corrections will be the same.

[BFG99]

I'm largely guessing based on my limited (but slowly expanding) understanding of WAAS/EGNOS. It was my understanding that all GPS satellite signals already accounted for the minimal possible ionosphere interference, and the WAAS calculated differential is the "greater than minimal". If that's true, then there can be times when a zero differential from the standard GPS is needed, which would mean a lock-on to a WAAS satellite would not result in a "D".

 

But again, I could be way off. I wouldn't be surprised.

 

As far as why different WAAS satellites would provide different differentials - again, guessing. But, there would be no reason for Garmins to lock onto 2 WAAS satellites simultaneously if they provided exactly the same differential. And I would assume the ionosphere differential would be somewhat different at each reference station.

[+GeoTrekker26]

I'm largely guessing based on my limited (but slowly expanding) understanding of WAAS/EGNOS. It was my understanding that all GPS satellite signals already accounted for the minimal possible ionosphere interference, and the WAAS calculated differential is the "greater than minimal". If that's true, then there can be times when a zero differential from the standard GPS is needed, which would mean a lock-on to a WAAS satellite would not result in a "D".

 

But again, I could be way off. I wouldn't be surprised.

 

As far as why different WAAS satellites would provide different differentials - again, guessing. But, there would be no reason for Garmins to lock onto 2 WAAS satellites simultaneously if they provided exactly the same differential. And I would assume the ionosphere differential would be somewhat different at each reference station.

 

Maybe you should read a little about WAAS before you post more silly speculation. What you think happens is actually impossible. How can a GPS transmitting satellite know what error is going to be encountered and be able to provide the differing corrections for the various locations the signal is being received?

 

Read here instead of guessing: How WAAS works. More in depth information is available here: Wikipedia WAAS article.

[Fangamon]

I'm largely guessing based on my limited (but slowly expanding) understanding of WAAS/EGNOS.

 

Try here for the basics on WAAS...

 

http://www.gpsinformation.org/dale/misc.htm#waas

 

[+andyakashrek]

Having turned waas off on my 550t the unit displays my position on the map much faster than if waas is enabled.Now I can park,boot the unit,put my boots on and it's ready to go. With waas on it takes @5 minutes to find my position. So,in Gloucestershire uk,it seems that,for me, waas off is the way to go.

[+ecanderson]

Having read all of the above, Fizzy's comments are of the few that consistently make any sense. To those unfamiliar with the methods and reasoning behind WAAS (or EGNOS), you'd best listen to what he's telling you. He seems to have a far better understanding of propagation and correction issues than most of those here who are producing only anecdotal information or pure conjecture. Trust me -- they didn't throw up all of those ground stations and use satellite bandwidth just for the fun of it. It serves a very definite purpose in significantly reducing one of the error sources in using GPS to determine receiver location.

[jholly]

Trust me -- they didn't throw up all of those ground stations and use satellite bandwidth just for the fun of it. It serves a very definite purpose in significantly reducing one of the error sources in using GPS to determine receiver location.

 

Agreed, if you're an aeroplane flying above ground level. For us mere mortals dipping in and out of valleys etc where getting an EGNOS lock is nigh impossible I find no benefit in it whatsoever.

But for those mere mortals traveling on the desert or large plains it makes perfect sense to have it on. Actually it makes perfect sense to have it on all the time. It certainly does not degrade the performance.

[+Team CowboyPapa]

Having read all of the above, Fizzy's comments are of the few that consistently make any sense. To those unfamiliar with the methods and reasoning behind WAAS (or EGNOS), you'd best listen to what he's telling you. He seems to have a far better understanding of propagation and correction issues than most of those here who are producing only anecdotal information or pure conjecture. .....

Huge Roger That!

[+Team CowboyPapa]

Trust me -- they didn't throw up all of those ground stations and use satellite bandwidth just for the fun of it. It serves a very definite purpose in significantly reducing one of the error sources in using GPS to determine receiver location.

 

Agreed, if you're an aeroplane flying above ground level. For us mere mortals dipping in and out of valleys etc where getting an EGNOS lock is nigh impossible I find no benefit in it whatsoever.

But for those mere mortals traveling on the desert or large plains it makes perfect sense to have it on. Actually it makes perfect sense to have it on all the time. It certainly does not degrade the performance.

10-4, now that you mention desert, I will be travelling through the Mojave Desert at N35.00, W117.55 next Friday and WAAS will be on. I see no reason not to have it on, it is always and advantage when there is WAAS(W)aquisition and never a detriment when not.

[+Team CowboyPapa]

Trust me -- they didn't throw up all of those ground stations and use satellite bandwidth just for the fun of it. It serves a very definite purpose in significantly reducing one of the error sources in using GPS to determine receiver location.

... For us mere mortals dipping in and out of valleys etc ....

How coincidentally applicable timewise, next weekend I will traveling up out of the Mojave Desert at 2600 ft to 7300 feet to the High Sierras on Nine Mile Canyon Road. I'll have WAAS functionality enabled and the GPSr fixed to my windshield mount and periodically check acquisition through canyons, valleys and high meadows.

[+Team CowboyPapa]

.... most of those here who are producing only anecdotal information or pure conjecture. ....

Now that you mention anecdotal and conjectural pontifications, I would like to mention my current studies regarding the EPE characteristic provided on most GPSrs. As has often been noted, correctly, the GPSr manufacturers consider the definition of exactly the quantitative nature of the EPE to be proprietary and therefore unrevealable. (Note that similarly neither will GM reveal the failure rate of ignition switches nor will Toyota disclose the frequency of carpeting to accelerator interference.) Consequently, I am engaged in gathering the applicable data with which I may determine the accuracy characteristics defining the EPE displayed on my GPSr.

[+ecanderson]

Trust me -- they didn't throw up all of those ground stations and use satellite bandwidth just for the fun of it. It serves a very definite purpose in significantly reducing one of the error sources in using GPS to determine receiver location.

 

Agreed, if you're an aeroplane flying above ground level. For us mere mortals dipping in and out of valleys etc where getting an EGNOS lock is nigh impossible I find no benefit in it whatsoever.

Geez, Suss -- you might want to consider checking the location in my profile before saying something like that. We don't have 'valleys', we have 'canyons'. Anyplace you could possibly live in the UK, no matter how 'hilly', we'd still call you a flatlander.

 

Still, where a WAAS bird is available, you can bet I'm locked onto it. Enabled 100% of the time.

[+andyakashrek]

You might get a WAAS lock where you are ... but I'm much further north than you. It's not that often my GPS can see an EGNOS satellite, hence my comment. As I said, 'where getting an EGNOS lock is nigh impossible I find it no benefit whatsoever'. If you can consistently get a good WAAS lock then great, if I could I might use it too

And I think I may be further north still.

[RamblinBear]

In my experience (having it enabled on my old Foretrex 101, GPSMap 60CSx, and now Etrex 30), having WAAS/EGNOS enabled makes no detriment to the performance of the receiver, and it can be a benefit. Living in the UK, it sometimes surprises me in which situations I do pick up EGNOS and in which I don't - and it doesn't always follow expectations. Recently, in a fairly deep valley in the Lake District, I got an EGNOS fix pretty quickly, and yet sometimes up on the top of the Black Mountains (a dissected high moorland/mountain plateau) I don't get an EGNOS signal that quickly. I work on the basis that the performance/battery hit from having it enabled is negligible so I have it enabled. Certainly, having GLONASS enabled makes a big difference in terms of reliability of getting a position fix at the outset - but that's a different issue.

 

In my working life, I have the pleasure of regularly using a professional-grade GNSS receiver (for public rights of way work), which picks up GPS, GLONASS, and WAAS/EGNOS, and will report statistics on its position quality (HDOP, age of correction signals and standard deviations of Lat., Long., and Height). The manufacturer's specifications give an accuracy of generally better than 0.5m RMS under good conditions with WAAS/EGNOS enabled (and I routinely see better than that out in the field). What I can tell you is that on that machine, the difference between having EGNOS on and not is like night and day - if the receiver is of sufficient quality, you will see a big improvement in accuracy with EGNOS/WAAS enabled. What I can also say from using that machine is that EGNOS (which has satellites in the southern sky - as seen from the UK) can be somewhat sensitive to obstruction from the south - i.e. from high land-masses, tall buildings, deep forest, and this is something which I have to be mindful of when conducting surveys. I suspect it is this feature which may give rise to Sussamb's observations and reservations about it.

 

To be brutally honest, with the consumer-grade chipsets which Garmin will be using in our devices, WAAS/EGNOS may make a bit of a difference, but in most situations, it's not going to be as apparent as on the pro-grade equipment. The question is do you want an Etrex 30 for about £150 (and 140 grammes), or a Spectra Precision MobileMapper 120 for about £3500 (and 620 grammes)?

Edited August 2, 2014 by RamblinBear