To WASS or not to WAAS

[+Barbarnero]

Why should or shouldnt I enable WAAS on my GPSr. what are some of the benefits and or disadvantages to using WAAS for geocaching purposes?

 

Thanks

Barbarnero

[+hogrod]

More accuracy if you can actually get WAAS near the cache hide, but some people claim worse battery life. I've never really noticed a significant difference in battery life so who knows.

[lewis82]

Pros: Way better accuracy when you receive WAAS signals. It can be as low as 2 m.

 

Cons: Slightly lower battery life (however, unless you have a Colorado, battery life shouldn't be a worry).

 

Use it

[sbfireman]

WAAS takes advantage of ground based signals to provide increased accuracy. Although designed for aviation, there are benefits to all GPS users. Here's some info that may help you in your decision:

 

http://www.faa.gov/about/office_org/headqu.../gnss/faq/waas/

 

I'd say enable it on your GPS unit, try and see for yourself.

 

Cheers,

 

Michael

[+LifeOnEdge!]

...

Cons: Slightly lower battery life (however, unless you have a Colorado, battery life shouldn't be a worry).

...

 

I love the continued Colorado bashing. It's uncalled for.

 

WAAS does not significantly affect battery life in either the Garmin Colorado or most newer GPS units.

 

While you may not get a significant improvement in accuracy, I believe the effective accuracy is better. It can't hurt to have it turned on and since it doesn't greatly degrade battery life, I would turn it on and leave it on.

 

The easiest way to test it out would be on a stationary landmark on or near your property. Take a one minute reading, record the coordinates, and compare that with various satellite configurations with and without WAAS enabled. I would alternate which is tested first. This also reduces the number of times you turn on and off WAAS by 50%. A quick sketch in a data book of the satellite pattern/configuration will give you a handy reference for future comparisons.

Edited February 18, 2008 by LifeOnEdge!

[+victorymike]

If you don't know where the ground stations are around you, don't use it. If you are more than 200 miles from a ground station, don't use it either.

 

WAAS is a series of geo-synchronous satellites with ground based stations that transmit position corrections based on changing weather patterns. Your GPS works on the principle of transmitting signals at the speed of light in a vacuum...which works great in outer space. But we all know that the Earth has an atmosphere. And in that atmosphere changing weather patterns also effect the speed that those signals are transmitted from the satellites. It is critical that the speed correction factor is accurate to the nano-second. So ground based stations monitor the weather and can send correction factors to the geosynchronous satellites which, in turn, send them to your GPS...just like a GPS satellite does. It is a form of differential GPS.

 

The ground based stations are typically found near major airports. Makes sense, since it is the airport industry that developed WAAS for use in their planes anyway.

 

If you are not in that weather pattern (basically over 200 miles from the ground station) and WAAS is enabled then you are getting correction signals even though your weather pattern is different. So you are getting ERRORs incorporated into your GPS position. That is why you need to know the answers to the question that I posed up top.

 

In Michigan I am always around 180 miles from the nearest ground station so I leave WAAS off.

[shivia]

...The ground based stations are typically found near major airports. Makes sense, since it is the airport industry that developed WAAS for use in their planes anyway...

- hello. do you know some website showing these ground stations locations? I just curious to know the closest ground station from Quebec, Canada. thanks.

[+gpsblake]

It doesn't matter, either having WAAS on or off will get you to 99 percent of geocaches. Most Garmins by default have it turned off while most Magellans have it turned on by default. I've done several measurements using WAAS on and off using adjusted USGS benchmarks and found it doesn't make a lick of difference, I'm always within 10 feet and quite often within 6 feet which is the margin of error in the DD MM.xxx system.

[+victorymike]

From Wikipedia: As of October 2007 there are 38 WRS's, twenty in the contiguous United States (CONUS), seven in Alaska, one in Hawaii, one in Puerto Rico, five in Mexico, and four in Canada.

 

Now: To find the locations...

 

Unfortunately this doesn't list the location by specific state/city...that is hard to find.

Edited February 18, 2008 by victorymike

[+victorymike]

The thing about using WAAS...it ONLY works if the person who placed the cache used it too. And since most don't...what does WAAS really do for you? No matter what you will be close enough to locate any cache.

[+Red90]

It does not matter whether you are near a station or not. The GPS is smart enough to determine the type and amount of corrections to use based on your actual location.

 

It is always helpful to use. In my experience, with the new WAAS birds, it is easy to hold a WAAS lock pretty much all of the time and the improvements in accuracy are worth having for Geocaching use.

[+victorymike]

There are only 2 WAAS Satellites...Pacific and Atlantic. Multiple ground stations.

[+JohnnyVegas]

I have always enabled WAAS in my GPS. I have never read anything that would give me reason to disable WAAS in my GPS. In the early days people would say it would drain batteries in a GPS, I have never seen any added drain in any GPS I have ever used from leaving WAAS enabled. As far a proximity to a ground station, this is the first time I heard that one. My guess there is nothing to this claim.

 

While I have seen claims in forums re. battry drain using WAAS, no one has mentioned anything about the exact increase in current from using WAAS.

Edited February 19, 2008 by JohnnyVegas

[+EraSeek]

Yes, use WAAS and beware of people who don't know what they are talking about.

Weather is not a factor. Distance from a ground station is not a factor with WAAS. WAAS does not track weather. It tracks Space weather. The Ionosphere. An active ionosphere can slow a signal and cause an inaccurate position, but the GPS signal is a frequency that was chosen because it is largely unaffected by terrestrial weather. The idea that distance from ground stations holds true with DGPS ground transmitted corrections, but not for the WAAS system which builds a model of corrections and uses your GPS's position to implement those corrections. As long as you are within the WAAS correction area (basically all of North America) you will get equal benefit from the system and be able to apply the needed corrections for your position.

 

WAAS realtime correction area http://www.nstb.tc.faa.gov/RT_VerticalProtectionLevel.htm

Does weather affect GPS: http://www.gpsinformation.net/gpsclouds.htm

 

"WAAS improves accuracy by correcting for errors in the satellite's clock and orbit, and for ionospheric (upper atmosphere) errors." One nano-second (one billionth of a second) of error equals one foot of position error. What WAAS does is collect data at stations, which sends this data to a master station which uses this data to make a universal model of corrections, a net of corrections, send this data to the WAAS sats which sends these corrections to your GPS, which figures out where it is in the net of corrections and uses the nearest data to correct your time and position. The position of the stations at this point are irrelavant.

[+JohnnyVegas]

The thing about using WAAS...it ONLY works if the person who placed the cache used it too. And since most don't...what does WAAS really do for you? No matter what you will be close enough to locate any cache.

 

And since most don't

That is an interesting claim

I have never seen a box to check asking if I used WAAS when placing a cache. I have never seen a study to determine which caches had been placed using WAAS.

[+GPSlug]

The thing about using WAAS...it ONLY works if the person who placed the cache used it too. And since most don't...what does WAAS really do for you? No matter what you will be close enough to locate any cache.

 

And since most don't

That is an interesting claim

I have never seen a box to check asking if I used WAAS when placing a cache. I have never seen a study to determine which caches had been placed using WAAS.

 

If the cache was placed on a day with a quiet ionosphere, and you're searching on a day with an active ionosphere, WAAS will certainly help you whether the placer was using it or not.

 

Even if the cache was placed on a bad day, how would compounding the error by having your position be worse not hurt you? It's not like you're going to be wrong in exactly the same direction. That's like saying, "the placer powered up their receiver at the cache site and recorded the first position it calculated, so I should do that too."

[+JohnnyVegas]

The main point in my reply was the statement that most caches are placed without the aid of WAAS

 

 

As far as WAAS, leave it on, those the say turn it off really do not know what they are talking about.

[+doingitoldschool]

I bought a used Visat that started to go blank, with a single vertical bold line, regardless of battery life. I was pointed to a thread in here that blamed a glitch in the software when the Garmin has WAAS enabled. I turned WAAS off, and it hasn't happened since.

I have also heard that forest cover interferes with WAAS, (and of course regualr signals as well) and most caches around me are in or near heavy forest.

So I do not go a'WAASling with my GPS.

[+victorymike]

Okay, I accept defeat. Upon further research I see where you pro-WAAS-ers are coming from. But I swear that I didn't just pull that 200 mile radius from a ground station thing out of my...you know. Then again, I haven't further researched WAAS since 2003. A lot has changed and websites have been updated. As far as WAAS satellites go I know there are more than 2...but just 2 for the U.S...at least until this information was passed on to me...

 

Your post #12 in http://forums.Groundspeak.com/GC/index.php?showtopic=185697 is not strictly true. In the USA only 2 can be seen, but if you have a Magellan that's been reset only 1 will ever be seen (it's still going to look for the long gone PRN122). There are actually 7 WAAS/EGNOS/Japanese satellites in the series now. see http://celestrak.com/NORAD/elements/sbas.txt

AOR-E (EGNOS/PRN 120) 1 24307U 96053A 08048.66246862 -.00000137 00000-0 10000-3 0 20662 24307 0.0746 311.0861 0007010 7.9258 50.9474 1.00271084 41922IOR-W (EGNOS/PRN 126) 1 25153U 98006B 08048.71146378 .00000127 00000-0 10000-3 0 90802 25153 0.4165 8.5083 0004594 318.7703 100.8276 1.00269931 36801

ARTEMIS (EGNOS/PRN 124) 1 26863U 01029A 08045.09162414 .00000125 00000-0 10000-3 0 41122 26863 6.2300 76.1018 0004363 263.3958 218.3866 1.00275320 25240

MTSAT-1R (MSAS/PRN 129) 1 28622U 05006A 08048.36110413 -.00000293 00000-0 10000-3 0 51202 28622 0.0321 36.4712 0001621 108.3819 271.8687 1.00268724 10887

ANIK F1R (WAAS/PRN 138) 1 28868U 05036A 08048.41477119 -.00000087 00000-0 00000+0 0 45292 28868 0.0526 109.7006 0002620 208.9801 230.0925 1.00272272 9023

GALAXY 15 (WAAS/PRN 135)1 28884U 05041A 08048.56002566 .00000065 00000-0 10000-3 0 39882 28884 0.0177 297.6256 0002273 23.2580 254.6140 1.00272870 8612

MTSAT-2 (MSAS/PRN 137) 1 28937U 06004A 08048.61768639 -.00000257 00000-0 10000-3 0 37742 28937 0.0197 356.9208 0003276 349.2430 168.0908 1.00268512 7367

Now, in my GPSr, a 12 channel receiver, if WAAS is ON, 2 of the channels are dedicated to WAAS and therefore only 10 are left for the regular GPS sats. If WAAS is OFF all 12 channels are available. I've seen mention of 14 channel receivers to give you every possible chance to receive every possible satellite. But actually with 30 satellites up there (skip PRN07 and PRN32 right now) you still can't see ALL.

 

But I still say that people enabling or disabling WAAS at will you may be closer or further from the cache placer's coordinate. In then end it does not matter. WAAS enabled or WAAS disabled...your GPS will still put you close enough to find the cache.

 

Although I have WAAS disabled I average my coordinates for 5 minutes when placing a cache. And have had nothing but compliments on accuracy.

[+JohnnyVegas]

I have also heard that forest cover interferes with WAAS, (and of course regualr signals as well) and most caches around me are in or near heavy forest.

So I do not go a'WAASling with my GPS.

If that is an older Vista, the problem is with the GPS chipset, not WAAS. The early versions of the e-trex line do not have very sensitive chip sets.

Edited February 20, 2008 by JohnnyVegas

[tomc61]

Here is a good web page about WAAS

http://gpsinformation.net/waasgps.htm

[GPS-Hermit]

I was hiking this weekend and I finally reached the top of a mountain and a gas pipeline right of way. With blue clear skys I looked at my GPS and I almost all the satelite bars were tall and black and all had 'D's in them. Is this 'D' I am seeing and tall black bars mean I am getting a WAAS signal. My accuracy came down to 8 ft which almost never happens.

Edited February 20, 2008 by GPS-Hermit

[+EraSeek]

Yes, the D's are the WAAS corrected satellites.

[+julianh]

Yes, the D's are the WAAS corrected satellites.

Note that if you are outside the valid coverage region of the ground stations (i.e. outside North America, and possibly Europe - I don't know the status of WAAS in Europe), and you turn WAAS on, you will still see the "D" on the satellite bars if your GPSr can "see" one of the WAAS satellites. (On east coast Australia, I can see one of them almost all of the time, if I turn WAAS on.) I suspect this is why many people erroneously believe that they get better accuracy with WAAS on - because the unit implies this is the case. However, the GPSr apparently has no way of knowing whether the WAAS corrections it is receiving are valid at your current location. They are definitely NOT valid in Australia at present, and can actually degrade the accuracy of your location fix, whatever the unit thinks.

 

If you are outside North America / Europe - TURN WAAS OFF!!!!

[+Mudfrog]

The main point in my reply was the statement that most caches are placed without the aid of WAAS

 

 

As far as WAAS, leave it on, those the say turn it off really do not know what they are talking about.

Well, i certainly don't know all the ins and outs of WAAS but i do know first hand that it doesn't help me in finding or hiding caches. I started out caching in 02 with an old Garmin unit that didn't have WAAS and found quite a few caches with it. I later decided to upgrade to a newer unit in 03 and made sure that it incorporated WAAS because i thought it was a feature that would really help. What can i say, i gave it good college try and found that it made no difference at all whether it was enabled or not. The one thing i did notice is that it had alot of trouble keeping the differential lock under tree cover (which is where alot of the caches i find are). For Christmas 04, my Wife bought me another GPSR that had mapping capabilities. As with the previous unit, i used this one with WAAS enabled for several days and found that it just didn't seem to make any difference when finding caches.

 

As far as battery life goes, it did seem to shorten it a little bit on both units...

 

Btw, i cache with 4 other cachers routinely that all use their units with WAAS enabled. Enabled or not, we almost always (i would say at least 99% of the time) end up looking in the same exact spot. That in itself is proof enough for me that i don't need it!

[+EraSeek]

Yes, the D's are the WAAS corrected satellites.

Note that if you are outside the valid coverage region of the ground stations (i.e. outside North America, and possibly Europe - I don't know the status of WAAS in Europe), and you turn WAAS on, you will still see the "D" on the satellite bars if your GPSr can "see" one of the WAAS satellites. (On east coast Australia, I can see one of them almost all of the time, if I turn WAAS on.) I suspect this is why many people erroneously believe that they get better accuracy with WAAS on - because the unit implies this is the case. However, the GPSr apparently has no way of knowing whether the WAAS corrections it is receiving are valid at your current location. They are definitely NOT valid in Australia at present, and can actually degrade the accuracy of your location fix, whatever the unit thinks.

 

If you are outside North America / Europe - TURN WAAS OFF!!!!

 

From pdops:

("To quote Garmin's software update page " A unit will not use a WAAS/EGNOS satellite if the unit's current position is outside of a given WAAS/EGNOS satellite's service volume." In Dale DePriest's DGPS and WAAS Information Page he states "If you receive a satellite but do not have any ionospheric data for your area the Garmin receivers with the latest firmware do detect this condition. They will not lock on a WAAS SV outside its coverage area. I think they should lock if no other WAAS capable SV covers the area and use the corrections for clock and ephemeris available while applying the internal ionospheric correction algorithm in this case but they don't seem to be this sophisticated." This means that when iono corrections are not available the clock and ephemeris corrections are also not applied. )

 

The corrections from the WAAS system comes in two forms. Corrections for clock and ephemeris, which are not location dependant, and Ionospheric corrections which are location dependant (your GPS's location).

If applied independant of the ionospheric corrections, (which are only valid within North America), then clock and emphemeris corrections will help outside the area because they are satellite specific not location specific. However, if you try to apply the ionospheric corrections outside the correction area I can see how it can make things worse. Inside the correction area your GPS know what is valid corrections for you.

 

This is the area we are talking about for "all" corrections including ionospheric: http://www.nstb.tc.faa.gov/RT_VerticalProtectionLevel.htm

 

I don't see the plot anymore for the WAAS area without ionospheric corrections, but it covers much more of the western hemsphere.

Edited February 20, 2008 by EraSeek

[+julianh]

From pdops:

("To quote Garmin's software update page " A unit will not use a WAAS/EGNOS satellite if the unit's current position is outside of a given WAAS/EGNOS satellite's service volume." In Dale DePriest's DGPS and WAAS Information Page he states "If you receive a satellite but do not have any ionospheric data for your area the Garmin receivers with the latest firmware do detect this condition. They will not lock on a WAAS SV outside its coverage area. I think they should lock if no other WAAS capable SV covers the area and use the corrections for clock and ephemeris available while applying the internal ionospheric correction algorithm in this case but they don't seem to be this sophisticated." This means that when iono corrections are not available the clock and ephemeris corrections are also not applied. )

 

The corrections from the WAAS system comes in two forms. Corrections for clock and ephemeris, which are not location dependant, and Ionospheric corrections which are location dependant (your GPS's location).

If applied independant of the ionospheric corrections, (which are only valid within North America), then clock and emphemeris corrections will help outside the area because they are satellite specific not location specific. However, if you try to apply the ionospheric corrections outside the correction area I can see how it can make things worse. Inside the correction area your GPS know what is valid corrections for you.

 

This is the area we are talking about for "all" corrections including ionospheric: http://www.nstb.tc.faa.gov/RT_VerticalProtectionLevel.htm

 

I don't see the plot anymore for the WAAS area without ionospheric corrections, but it covers much more of the western hemsphere.

As Dale DePriest says at the start of his article ( http://www.gpsinformation.org/dale/dgps.htm ):

The information in this section is strictly conjecture based on study and observation. Garmin considers the inner-workings of their GPS receivers to be trade secrets so this information is not published.

 

In the web article he suggests that:

 

If you receive a satellite but do not have any ionospheric data for your area the Garmin receivers with the latest firmware do detect this condition. They will not lock on a WAAS SV outside its coverage area. I think they should lock if no other WAAS capable SV covers the area and use the corrections for clock and ephemeris available while applying the internal ionospheric correction algorithm in this case but they don't seem to be this sophisticated. [My emphasis]

 

However, in the equivalent section of his downloadable PDF e-book "A GPS User Manual - Working With Garmin Receivers", he says:

 

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. 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. [My emphasis]

 

I don't know which of these two opinions is more up to date. I DO know that the description in the PDF e-book is more like what I actually see with my Summit HC (latest software version 2.50 GPS software version 2.60) in Eastern Australia - it WILL generate a WAAS lock, it WILL indicate differential corrections with a "D" on most satellite bars, and the reported accuracy is USUALLY slightly worse than with WAAS off (in clear sky conditions, I routinely get 3 metres reported accuracy with WAAS off, blowing out to 5 metres reported accuracy with WAAS on - not that I necessarily believe EITHER of these figures, nor do I necessarily consider the small reported difference to be significant!), and the ACTUAL accuracy in terms of finding geocaches or other waypoints does not seem to be significantly different either way.

 

The only people who REALLY know what a Garmin does with the WAAS signal when you are out of range of the ground-stations are Garmin themselves - and they ain't saying!

Edited February 20, 2008 by julianh

[+EraSeek]

Yes. I agree. It is a confused situation. You could try locating a known coordinate like a benchmark and compare your gps coordinates with that with WAAS on and then off, but also keep in mind that half of the corrections will be for clock and ephemeris and the other half will be for ionospheric delay in North America so you will only benefit from the clock and ephemeris corrections at best anyway. It will not help you all that much to have it on, especially with this question of how ionospheric errors are handled.

 

Ionosphere errors: 4m

Clock: 2.1m

Ephemeris: 2.1m

Edited February 20, 2008 by EraSeek

[+JohnnyVegas]

Yes, the D's are the WAAS corrected satellites.

Note that if you are outside the valid coverage region of the ground stations (i.e. outside North America, and possibly Europe - I don't know the status of WAAS in Europe), and you turn WAAS on, you will still see the "D" on the satellite bars if your GPSr can "see" one of the WAAS satellites. (On east coast Australia, I can see one of them almost all of the time, if I turn WAAS on.) I suspect this is why many people erroneously believe that they get better accuracy with WAAS on - because the unit implies this is the case. However, the GPSr apparently has no way of knowing whether the WAAS corrections it is receiving are valid at your current location. They are definitely NOT valid in Australia at present, and can actually degrade the accuracy of your location fix, whatever the unit thinks.

 

If you are outside North America / Europe - TURN WAAS OFF!!!!

and can actually degrade the accuracy of your location

Prove it

[+julianh]

Prove it

Well, I couldn’t let that challenge go unanswered, could I?!

 

Here are some web references on WAAS accuracy outside the coverage of the ground-stations:

 

1. GPSOZ – one of the biggest GPS specialists in Australia: http://www.gpsoz.com.au/WAAS.htm

 

First quote:

 

Here are some observations from GPSOZ's location. They are 4 samples taken over 12 hours each. Two receivers, Garmin GPSmap76 and a Magellan Meridian GPS, with and without WAAS enabled. Basically when using a WAAS capable GPS in Australia, turn OFF WAAS.

Garmin GPSMap 76 - WAAS Enabled http://www.gpsoz.com.au/images/Garmin_WAAS_On.jpg

Garmin GPSMap 76 - WAAS Disabled http://www.gpsoz.com.au/images/Garmin_WAAS_Off.jpg

Magellan Meridian GPS - WAAS Enabled http://www.gpsoz.com.au/images/Magellan_WAAS_On.jpg

Magellan Meridian GPS - WAAS Disabled http://www.gpsoz.com.au/images/Magellan_WAAS_Off.jpg

 

Second quote:

 

I am in Townsville S19.45 E146.15 and have been performing WAAS observations for some time. Satellite 47 is approx 45deg above horizon and azimuth of approximately 45 deg. Depending upon current satellite geometry, accuracy is improved or diminished. EPE of 1.5 metres have been achieved and also blow outs to 60 metres have been observed.

 

2. Johnny Appleseed – another of the biggest GPS specialist suppliers in Australia: http://www.ja-gps.com.au/dgpsprod.html

 

It is possible to "augment" these signals from other satellites or ground transmitters of known position, thereby increasing either reliability, or accuracy, or both. WAAS is currently available over US, some northern Pacific areas, and Europe (EGNOS). WAAS is still in Beta (test) mode. WAAS does NOT work in Australia.

 

3. GPSinformation.net – one of the best sources of GPS information on the internet: http://www.gpsinformation.net/waasgps.htm

 

This does NOT mean that you can be in England, Mexico, Canada or any other location very distant from the WAAS correction stations and expect the USA WAAS corrections to be useful even if you can receive the WAAS satellites. In fact, if you are in Europe, Africa, Australia or anywhere more than perhaps 500 miles away from the shores of the USA, the use of WAAS signals may well REDUCE the accuracy of your GPS fixes.

 

4. A typical Google search: http://sci.tech-archive.net/Archive/sci.ge...4/msg00299.html

 

The other day I had around 6 satellites all receiving WAAS corrections [in Sydney, Australia], but the position accuracy it calculated was about 35 meters, as opposed to 4-5 meters when WAAS was turned off with the same satellites.

 

I could go on, but that will do for now. These comments absolutely reflect my own observations and measurements with WAAS on and off here in east coast Australia. I figure that the above specialists PROBABLY have some idea what they are talking about. In particular – check out the plots from GPSOZ, and tell me that WAAS is ALWAYS beneficial when you are out of the range of the ground-station network!

[shivia]

On my 60csx, how do i know (or see) the iono and/or clock corrections? Is there the signs, icons or something else telling me there are corrections? thanks.

[+Red90]

On my 60csx, how do i know (or see) the iono and/or clock corrections? Is there the signs, icons or something else telling me there are corrections? thanks.

 

On the satellite page, it shows the letter "D" in the bars.

 

[+julianh]

On my 60csx, how do i know (or see) the iono and/or clock corrections? Is there the signs, icons or something else telling me there are corrections? thanks.

On all Garmin units, with WAAS turned on, you either get the "D" or you don't. Without the "D", you are not getting any WAAS corrections. If you get the "D" and you are in the ground-station coverage area (e.g. North America), you are presumably getting the full benefit of all WAAS corrections. As far as I know, if you get the "D" but you are outside the ground-station coverage area, there is no way of knowing which corrections the unit is applying, and which it is ignoring - because Garmin don't say.

[+JohnnyVegas]

Prove it

Well, I couldn’t let that challenge go unanswered, could I?!

 

Here are some web references on WAAS accuracy outside the coverage of the ground-stations:

 

1. GPSOZ – one of the biggest GPS specialists in Australia: http://www.gpsoz.com.au/WAAS.htm

 

First quote:

 

Here are some observations from GPSOZ's location. They are 4 samples taken over 12 hours each. Two receivers, Garmin GPSmap76 and a Magellan Meridian GPS, with and without WAAS enabled. Basically when using a WAAS capable GPS in Australia, turn OFF WAAS.

Garmin GPSMap 76 - WAAS Enabled http://www.gpsoz.com.au/images/Garmin_WAAS_On.jpg

Garmin GPSMap 76 - WAAS Disabled http://www.gpsoz.com.au/images/Garmin_WAAS_Off.jpg

Magellan Meridian GPS - WAAS Enabled http://www.gpsoz.com.au/images/Magellan_WAAS_On.jpg

Magellan Meridian GPS - WAAS Disabled http://www.gpsoz.com.au/images/Magellan_WAAS_Off.jpg

 

Second quote:

 

I am in Townsville S19.45 E146.15 and have been performing WAAS observations for some time. Satellite 47 is approx 45deg above horizon and azimuth of approximately 45 deg. Depending upon current satellite geometry, accuracy is improved or diminished. EPE of 1.5 metres have been achieved and also blow outs to 60 metres have been observed.

 

2. Johnny Appleseed – another of the biggest GPS specialist suppliers in Australia: http://www.ja-gps.com.au/dgpsprod.html

 

It is possible to "augment" these signals from other satellites or ground transmitters of known position, thereby increasing either reliability, or accuracy, or both. WAAS is currently available over US, some northern Pacific areas, and Europe (EGNOS). WAAS is still in Beta (test) mode. WAAS does NOT work in Australia.

 

3. GPSinformation.net – one of the best sources of GPS information on the internet: http://www.gpsinformation.net/waasgps.htm

 

This does NOT mean that you can be in England, Mexico, Canada or any other location very distant from the WAAS correction stations and expect the USA WAAS corrections to be useful even if you can receive the WAAS satellites. In fact, if you are in Europe, Africa, Australia or anywhere more than perhaps 500 miles away from the shores of the USA, the use of WAAS signals may well REDUCE the accuracy of your GPS fixes.

 

4. A typical Google search: http://sci.tech-archive.net/Archive/sci.ge...4/msg00299.html

 

The other day I had around 6 satellites all receiving WAAS corrections [in Sydney, Australia], but the position accuracy it calculated was about 35 meters, as opposed to 4-5 meters when WAAS was turned off with the same satellites.

 

I could go on, but that will do for now. These comments absolutely reflect my own observations and measurements with WAAS on and off here in east coast Australia. I figure that the above specialists PROBABLY have some idea what they are talking about. In particular – check out the plots from GPSOZ, and tell me that WAAS is ALWAYS beneficial when you are out of the range of the ground-station network!

 

In the articles you posted mention is made that there in not WAAS service in Australia, utill Australia spends the money on ground stations to support WAAS there will be no WAAS service in Australia, it takes more than a WAAS sattelite to get accurate WAAS corections. Unless there is a Ground station set up supply the data you cannot expect WAAS to work.

 

One writer says The other day I had around 6 satellites all receiving WAAS corrections [in Sydney, Australia Unless there are WAAS ground staitons working in Australia, there are no correstions for that area.

BTW---- DGPS is not the same as WAAS, DGPS requires that the GPS being used is connected t DGPS reciever.

 

and can actually degrade the accuracy of your location there is not real WAAS service in Australia.

 

The one article you linked was pulished in 2002 that is old in the world of technology, that article evan states that at the time the WAAS system was just being testing

Edited February 21, 2008 by JohnnyVegas

[+Red90]

I travel all over the world (including Australia) and never bother to turn WAAS off. I've never seen any strange accuracy problems.

[+julianh]

[in the articles you posted mention is made that there in not WAAS service in Australia, utill Australia spends the money on ground stations to support WAAS there will be no WAAS service in Australia, it takes more than a WAAS sattelite to get accurate WAAS corections. Unless there is a Ground station set up supply the data you cannot expect WAAS to work.

 

One writer says The other day I had around 6 satellites all receiving WAAS corrections [in Sydney, Australia Unless there are WAAS ground staitons working in Australia, there are no correstions for that area.

BTW---- DGPS is not the same as WAAS, DGPS requires that the GPS being used is connected t DGPS reciever.

 

and can actually degrade the accuracy of your location there is not real WAAS service in Australia.

 

The one article you linked was pulished in 2002 that is old in the world of technology, that article evan states that at the time the WAAS system was just being testing

So, JohnnyVegas - are you agreeing with me, or disagreeing?

 

In all of my posts on this thread, I think I have been 100% consistent in saying that if you are out of the region of coverage of the ground-stations, then WAAS is not fully functional, and can actually degrade accuracy somewhat. You challenged me to prove it, so I gave some evidence.

 

Yes, one of the articles I linked to was published in 2002 - but the status in Australia has not changed. There are no working ground-stations in Australia, and no current plans to develop them. I can't speak for the rest of the world - each country will have its own plans. (But I understand that current WAAS / EGNOS coverage is basically limited to North America and Europe.)

 

The point of the Sydney example I gave was that the GPSr unit suggests that you ARE getting WAAS corrections if you turn WAAS on and can see a WAAS satellite, because you get the little “D” symbols. Many users therefore assume that their accuracy is improved – and this is not necessarily the case. Granted, MOST of the time, the reduction of accuracy (if any) is negligible, but SOMETIMES, the error can be much more significant. Returning to the quote:

 

The other day I had around 6 satellites all receiving WAAS corrections [in Sydney, Australia], but the position accuracy it calculated was about 35 meters, as opposed to 4-5 meters when WAAS was turned off with the same satellites.

 

I don't think I ever suggested that DGPS and WAAS are the same thing. (By the way - DGPS can be used in Australia - if you have the necessary hardware etc.)

 

Let me be succinct:

 

If you are in the region of coverage of the ground-stations (e.g. North America) - by all means turn WAAS on - I don't imagine that it will make your accuracy any worse (although I could be wrong), and if you get a WAAS signal, it will improve your accuracy marginally. If I visit North America, I will certainly turn it on.

 

If you are out of the region of coverage of the ground-stations (e.g. Australia) – you might as well turn WAAS off - it will NOT correct for the ionosphere errors (which is the biggest single component of error that WAAS can address), and it can DEFINITELY degrade your accuracy from time to time (on at least some units - but I don't know for a fact whether this applies to ALL units - because Garmin don't say.)

 

Either way – WAAS on / WAAS off, regardless of your location, the accuracy of modern GPSrs is typically of the order of 3 to 6 metres most of the time, which will certainly be good enough to navigate down a road or find a geocache. This is all really an academic argument because – bottom line – it really doesn’t matter whether you have WAAS on or off (most of the time!), unless you need survey-precision, in which case you shouldn’t be using a consumer model GPSr anyway!

Edited February 22, 2008 by julianh

[+Red90]

Either way – WAAS on / WAAS off, regardless of your location, the accuracy of modern GPSrs is typically of the order of 3 to 6 metres most of the time, which will certainly be good enough to navigate down a road or find a geocache. This is all really an academic argument because – bottom line – it really doesn’t matter whether you have WAAS on or off (most of the time!), unless you need survey-precision, in which case you shouldn’t be using a consumer model GPSr anyway!

 

Actually I don't agree. Since the WAAS satellites were changed so that we can easily see them up here in the north, cache finding and placement accuracy has improved substantially.

 

Finding caches in Australia is always harder as the accuracy of the placements and when finding is not nearly as good. I'm serious, I see a big difference.

[+julianh]

Either way – WAAS on / WAAS off, regardless of your location, the accuracy of modern GPSrs is typically of the order of 3 to 6 metres most of the time, which will certainly be good enough to navigate down a road or find a geocache. This is all really an academic argument because – bottom line – it really doesn’t matter whether you have WAAS on or off (most of the time!), unless you need survey-precision, in which case you shouldn’t be using a consumer model GPSr anyway!

 

Actually I don't agree. Since the WAAS satellites were changed so that we can easily see them up here in the north, cache finding and placement accuracy has improved substantially.

 

Finding caches in Australia is always harder as the accuracy of the placements and when finding is not nearly as good. I'm serious, I see a big difference.

Have you tried turning WAAS off when you are in Australia? Maybe you ARE seeing "strange accuracy problems" when you have WAAS turned on in Australia, as you said in your earlier post!

 

Seriously, I agree that accuracy in Australia without WAAS generally won't be quite as good as in North America with WAAS. The point I am trying to make is that in Australia (and other regions outside the zone of coverage of the ground-stations), accuracy with WAAS on can be worse than with WAAS off.

Edited February 21, 2008 by julianh

[+Red90]

Have you tried turning WAAS off when you are in Australia? Maybe you ARE seeing "strange accuracy problems" when you have WAAS turned on in Australia, as you said in your earlier post!

 

Seriously, I agree that accuracy in Australia without WAAS generally won't be quite as good as in North America with WAAS. The point I am trying to make is that in Australia (and other regions outside the zone of coverage of the ground-stations), accuracy with WAAS on can be worse than with WAAS off.

 

Before 48 and 51 were in service, you would rarely have a WAAS lock at my location (N51 W114) and the accuracy was as you would expect with WAAS off and the same as what I found in Aussyland. Since those sats became live, you can maintain a WAAS lock 90% of the time. Cache placement accuracy and finding accuracy has improved a lot since that time.

 

What I'm saying is that I notice NO DIFFERENCE in accuracy with WAAS on or off when outside of the WAAS area. Like I say, I travel around the world a fair bit. I'm also interested in mapping and GPS accuracy so it is something I pay attention to all of the time.

[+EraSeek]

Quite awhile back there used to be a poster on these forums named Kerry. He lived in aussieland and was a bit of an expert on gps's and how averaging was not advantagous after SA was put to rest, and also how WAAS degraded your position if used outside the coverage area such as Australia. Things have changed since then and what those changes are leaves me a bit up in the air on the issue. Those changes as I understand it mostly include Garmin's onetime statement that if outside the coverage area WAAS will not be used. Before that there were statement I recieved from Raytheon I believe that WAAS would be helpful because of the non-ionospheric corrections. However it seems from Kerry ionospheric corrections will cause degradation in position.

 

Here really is the argument. If you are recieving ionospheric corrections outside the coverage area one of two things are happening. Bogus corrections (perhaps the nearest data points which may be thousands of miles away) may be applied causing a worse position, or two, ionospheric corrections will be zero, overriding the pre-programed base correction in the unit and every unit software (or is it firmware?) causing a worse position because now there is no compensation at all.

 

However, if Garmin was clever enough to allow corrections blocking ionospheric corrections outside the correction area, then that would benefit all.

 

With the coming duel citizen band gps in around 2013, ionospheric corrections will be had without WAAS and availible to all....but there will be no satellite and clock correction with that system.

 

Just my layman's understanding of the issue.

[+julianh]

Have you tried turning WAAS off when you are in Australia? Maybe you ARE seeing "strange accuracy problems" when you have WAAS turned on in Australia, as you said in your earlier post!

 

Seriously, I agree that accuracy in Australia without WAAS generally won't be quite as good as in North America with WAAS. The point I am trying to make is that in Australia (and other regions outside the zone of coverage of the ground-stations), accuracy with WAAS on can be worse than with WAAS off.

 

Before 48 and 51 were in service, you would rarely have a WAAS lock at my location (N51 W114) and the accuracy was as you would expect with WAAS off and the same as what I found in Aussyland. Since those sats became live, you can maintain a WAAS lock 90% of the time. Cache placement accuracy and finding accuracy has improved a lot since that time.

 

What I'm saying is that I notice NO DIFFERENCE in accuracy with WAAS on or off when outside of the WAAS area. Like I say, I travel around the world a fair bit. I'm also interested in mapping and GPS accuracy so it is something I pay attention to all of the time.

OK - I'm going to have to eat some "humble pie"!

 

My old yellow eTrex and Vista (B&W) used to DEFINITELY show degraded accuracy from time to time with WAAS turned on in Australia. (Both units are now "retired", but were still being used in late 2007.) Most of the time, the effect was small (usually not even noticeable), but occasionally I would see large excursions in reported accuracy with WAAS on, and these would disappear immediately I turned WAAS off. Accordingly, after a bit of experimentation, I just left WAAS off. The links I have given above convinced me that the issue was that the Garmin firmware / software for these units was receiving a WAAS signal, and was incorrectly applying the ionosphere corrections in Australia, outside the range of the ground-stations.

 

I now have a Summit HC, running the latest software (version 2.70). I have just run a couple of 12-hour static tests. Each test was run over the same 12-hour period on consecutive nights, so that they would see pretty much the same constellation of satellites, and at the same fixed location with good (but not perfect) view of the sky. In both cases, I let the unit "bake" for half an hour before starting logging, to make sure both tests had a full complement of signals at the start of the test. Weather on both nights was clear and fine (although that shouldn't matter much). Here is what I found:

 

WAAS on: Mean radial error over the 12-hour test was 2.04 metres; maximum radial error was 5.40 metres; Standard Deviation of radial error was 1.30 metres. This means that the reported location should be within about 2 * 1.30 = 2.60 metres of true position, 95% of the time (under similar operating conditions).

 

WAAS off: Mean radial error over the 12-hour test was 2.35 metres; maximum radial error was 7.47 metres; Standard Deviation of radial error was 1.24 metres. This means that the reported location should be within about 2 * 1.24 = 2.48 metres of true position, 95% of the time (under similar operating conditions). (Yes, that's right - the measured statistical variation was actually slightly LOWER with WAAS off, but I don't believe this is a statistically significant difference.)

 

In both cases, the accuracy I have analysed is consistent with what the unit was reporting - showing an accuracy of 3 m to 4 m most of the time, occasionally down to 2 m, occasionally up to 5 or 6 m. In the "real world", where you are moving around, sometimes going under trees or between tall buildings, and your satellite reception is coming and going, you wouldn't achieve this degree of accuracy.

 

I therefore tentatively conclude that there is no statistically significant difference between WAAS on and WAAS off for this particular unit in Australia. I am guessing that the latest Garmin software MAY be using the clock and ephemeris corrections, but MAY be ignoring the ionosphere corrections, when you are out of range of the ground stations (but this is just speculation on my part). I do not believe this was the case for the older units, which CERTAINLY showed large errors from time to time with WAAS on. (It is also possible that the two 12-hour test windows happened to not show the issues which MAY still arise from time to time - again, pure speculation on my part!)

 

In summary:

 

If you have a late model Garmin, with current software, there MAY be no disadvantage to having WAAS turned on when out of the range of the ground-station network. However, there is also no demonstrated advantage.

 

With some older units (and possibly some newer units?) you WILL sometimes see reduced accuracy with WAAS turned on when out of range of the ground stations. Most of the time, the accuracy will PROBABLY be pretty much the same either way.

 

Now, where is my knife and fork .....

Edited February 22, 2008 by julianh

[+Klemmer]

I don't think you need to eat crow. That was some interesting testing you did. I've done quite a bit of reading recently on WAAS, and just finished writing an article on DGPS and WAAS for an on-line mag. It's really quite simple: IF YOU ARE NOT IN A WAAS COVERAGE AREA, TURN OF YOUR WAAS.

 

Sure, it is possible your newer unit may ignore WAAS when it should. But from my reading (and not just forums), and talking with knowledgeable industry folks, there will not be any significant improvement outside a WAAS covered area. Why risk it? Just turn it off.

 

Or, if you need more precision, learn about DGPS, and buy the 300 KHz band receiver for it, if you are within about 300 miles of one of the 200 or so stations in the world. Or, learn about the various "soon to come" GPS Augmentations that might be implemented in your area of the world, such as Airservices Australia's Ground-based Regional Augmentation System (GRAS), currently under development. Those particular augmentation signals are planned to be broadcast on VHF aviation radio frequencies, so unfortunately they might not be much use to geoacachers in Australia.

 

On a slightly different note, since you East Aussies do have a decent look at the Pacific WAAS satellite, possibly Australia could join the "WAAS club", kick-in with the US, and build some WAAS ground stations. Canada & Mexico did do exactly that. Maybe write your Parliamentary representative?

Edited February 22, 2008 by Klemmer & TeddyBearMama

[+EraSeek]

Just a couple of notes.

 

The "accuracy reading" or "EPE" on GPS's is just a guestimate and should not be taken as gospel. My older unit would display a much higher number when you first turn WAAS on and take some time to drop down. My newer unit shows no real difference on or off.

 

You mentioned that you did your tests at night. At night there is basically very little ionospheric activity, and thus very little correction or difference on or off. You might try again during mid day when things are most active.