Accuracy, Jumps, And Waas

[+shunra]

Today was my first day out caching with my new Map76S, which is a significant upgrade from the Magellan Blazer12, which I used for my first 129 finds.

 

The Blazer12 lacked a final digit, and coordinates had to be enteres as DD MM.MM, rather than in the more accurate DD MM.MMM format, which is used by all contemporary GPSrs. Likewise, when zooming in on a cache, the smallest unit was 0.01 mile, and next was 0.00 - no distance in ft was displayed. When I got to 0.00, I knew I was time to start looking around.

 

With my new Map76S, the accuracy is supposed to be much better - in terms of marking the location itself, as well as in terms of guiding me to that location. However, what do I make of it that when I get to - say - 30 ft from the cache and then stand still, the unit still perceives me as moving (in the best case) or jumping dozens of feet back and forth? This was reflected on all the screens, including the breadcrumbs on the map, butd by the direction of the arrow on the electronic compass, which I switched on every now and then in order to see in which direction I should walk those last few feet. Switching WAAS on or off made no difference. (What's the purpose of switching WAAS on or off anyway? If it's an improvement, why not have it always on?)

 

Does anyone have some good ideas for me about how to use a MODERN GPS?

 

Thanks!

[+Learned Gerbil]

GPS is never accurate to 0 feet. Once it starts jumping arround you are close to the cache, and withing the limits of the system. At that point standing still to improve averaging may help, but on the whole you need to explore your locality (in all directions).

 

You may find that circling the area at about 60 feet will give you a series of pointers allowing you to narrow down the location of the cache by triangulation, but this still won't be very precise.

 

As I understand it, WAAS is all about eliminating atmospheric factors so will not help you get closer than the 20 or 30 feet that most GPSr's can achieve.

[+PDOP's]

(What's the purpose of switching WAAS on or off anyway? If it's an improvement, why not have it always on?)

If you're in a location where your receiver can't pick up the signals from the WAAS satellites in can make sense to turn WAAS off. Having it turned on uses more power and reduces the number of regular GPS satellites that you can receive. For more on this see this web site.

[+Renegade Knight]

On WAAS having it on uses batteries and noticably slows down the update rate on my GPS V. This is especially annoying when you get close to a cache as the unit will tend to jump aroud a bit since as you wait for updates while tying to find ground zero.

[+shunra]

(What's the purpose of switching WAAS on or off anyway? If it's an improvement, why not have it always on?)

If you're in a location where your receiver can't pick up the signals from the WAAS satellites in can make sense to turn WAAS off. Having it turned on uses more power and reduces the number of regular GPS satellites that you can receive. For more on this see this web site.

Thanks, LG, PDOP and RK. I read the information about WAAS you linked to. Would it be correct to summarize and say that (1) WAAS uses batteries, (2) it wastes two channels, (3) doesn't work anyway when in battery saving mode (but still wastes more power and channels?), (4) needs wide open areas, and (5) was not meant to improve accuracy in the first place, so we'd better turn it off, except on the water, perhaps?

[+Sparky-Watts]

It's really interesting to hear the amount of people that think WAAS will help them, regardless of where they are. I'm in the breadbasket of the US, and I don't think I could lock a WAAS satellite if I tried, yet there is a remarkably high number of people that are nowhere near the effective area of WAAS satellites that claim their accuracy is better because of WAAS. Never used it, won't till it is proven to enhance my accuracy.

[+PDOP's]

Thanks, LG, PDOP and RK. I read the information about WAAS you linked to. Would it be correct to summarize and say that  ....

(1) WAAS uses batteries,

 

Yes

 

(2) it wastes two channels

 

It might be more accurate to say it uses two channels. Most of the time you'll be getting a fix with 10 or less GPS satellites anyway.

 

(3) doesn't work anyway when in battery saving mode (but still wastes more power and channels?)

 

Yes

 

(4) needs wide open areas

 

Yes you need an unobscured view to the south.

 

(5) was not meant to improve accuracy in the first place, so we'd better turn it off, except on the water, perhaps?

 

Yes it was designed as an aid to aircraft navigation where a clear view of the WAAS sateillites is not a problem. Under the right circomstances it can improve your accuracy on the ground. I live at 53ºN and have been able to get some good results on benchmarks in Canada. Under normal field conditions it's not much use.

 

Edited for spelling

Edited December 29, 2003 by PDOP's

[+fizzymagic]

It's really interesting to hear the amount of people that think WAAS will help them, regardless of where they are.  I'm in the breadbasket of the US, and I don't think I could lock a WAAS satellite if I tried, yet there is a remarkably high number of people that are nowhere near the effective area of WAAS satellites that claim their accuracy is better because of WAAS.  Never used it, won't till it is proven to enhance my accuracy.

Wow. If this level of ignorance about WAAS is widespread, then I can understand why there is such resistance to its use.

 

You certainly can use WAAS in the central US; it should work quite well. You do not need a continuous link to the WAAS satellite, especially with Magellan receivers. They can continue to apply WAAS corrections for about 10 minutes without any view of the satellite at all.

 

Exactly where do you think the "effective area" of WAAS is? FYI, it covers the contiguous 48 states completely. The midwest is entirely covered. And the WAAS corrections to the ephemeris work globally, not just in the covered areas. Thus, there is no place on Earth where WAAS corrections will not improve accuracy, unless your GPS has a defective WAAS correction algorithm, as is the case for many (especially older) Garmin units.

 

It has been shown many times, by many people, that WAAS improves the accuracy of your position measurement. That improvement may or may not show up on your GPS unit's estimated accuracy, but anyone who trusts that number doesn't understand the word "accuracy" anyway.

 

Unless you are using an older Garmin unit, I recommend using WAAS whenever you care about the accuracy of your readings.

[+fizzymagic]

(1) WAAS uses batteries,

 

In general, no. Only on some Garmin units.

 

(2) it wastes two channels

 

No. The geostationary WAAS satellites can actually be used for position determination as well as correction, by a GPS unit that knows how to do so. My Magellan does.

 

(4) needs wide open areas

 

No, once initialized it can work quite well in areas with only intermittent Southern views.

 

(5) was not meant to improve accuracy in the first place, so we'd better turn it off, except on the water, perhaps?

 

Not true. It was designed to improve accuracy, and it does. The accuracy improvement is best in areas with ground stations, as the continental US, but properly-implemented WAAS code will improve accuracy everywhere.

 

----------------------------------

 

PDOP, your page on WAAS contains a couple of rather serious errors.

 

First, WAAS corrections do not require a continuous view of the Southern horizon. If used in accordance with the standard, they only require about 30 seconds of data every 10 minutes or so. I find that my SporTrak is able to use WAAS corrections effectively more than 90% of the time, once it has had a chance to initialize the WAAS data.

 

Second, WAAS only uses extra power on Garmin units. For Magellan units, power consumption with and without WAAS is the same. I also believe that this is true for the GPS V and other newer Garmin units.

 

I don't think you have this on your page, but there is a widespread misconception that WAAS use can actually reduce accuracy. This perception comes from a defect in Garmin's algorithm for using WAAS corrections; when the corrections for all satellites were not available, the Garmins would only use WAAS-corrected satellites for position determination. I believe that Garmin has fixed this bug in their newest firmware, and this effect never applied to Magellan units anyway. I would suspect that your 76S probably still has the defect.

 

Actual real-world data has shown that WAAS is superior to other DGPS systems. It is terribly useful for many geocaching situations, in which careful coordinates of the cache location were never taken in the first place, but that certainly doesn't mean it doesn't improve accuracy.

[+Renegade Knight]

WAAS does work. My EPE is normally single digit with it on. 15' with it off. I've had one person at one of my caches mention an EPE of 3' with WAAS on.

 

It really does work. It just happens to slow down the refresh rate of my GPS which gets in the way of how I go about caching.

 

I believe my manual for the GPS V said it will use more batteries, but I could be wrong and I doubt I could find the manual to confirm it.

Edited December 30, 2003 by Renegade Knight

[+Sparky-Watts]

It's really interesting to hear the amount of people that think WAAS will help them, regardless of where they are.  I'm in the breadbasket of the US, and I don't think I could lock a WAAS satellite if I tried, yet there is a remarkably high number of people that are nowhere near the effective area of WAAS satellites that claim their accuracy is better because of WAAS.  Never used it, won't till it is proven to enhance my accuracy.

Wow. If this level of ignorance about WAAS is widespread, then I can understand why there is such resistance to its use.

 

You certainly can use WAAS in the central US; it should work quite well. You do not need a continuous link to the WAAS satellite, especially with Magellan receivers. They can continue to apply WAAS corrections for about 10 minutes without any view of the satellite at all.

 

Exactly where do you think the "effective area" of WAAS is? FYI, it covers the contiguous 48 states completely. The midwest is entirely covered. And the WAAS corrections to the ephemeris work globally, not just in the covered areas. Thus, there is no place on Earth where WAAS corrections will not improve accuracy, unless your GPS has a defective WAAS correction algorithm, as is the case for many (especially older) Garmin units.

 

It has been shown many times, by many people, that WAAS improves the accuracy of your position measurement. That improvement may or may not show up on your GPS unit's estimated accuracy, but anyone who trusts that number doesn't understand the word "accuracy" anyway.

 

Unless you are using an older Garmin unit, I recommend using WAAS whenever you care about the accuracy of your readings.

Whatever. I quit reading your drivel after you called me ignorant.

[+PDOP's]

FizzyMagic

 

Thanks for your comments ( and for Geo Calc too )

 

I based most of my page on what I've read on the net and mainly from Dale DePriest's website as well as my own experiences.

 

At 53N I cannot get the WAAS geo sats under any tree cover at all. Dale states that for Garmin receivers "even if the GEO is lost again, differential corrections will continue to be applied for about 2 minutes." So at least for me WAAS isn't much good under normal field conditions.

[+fizzymagic]

Whatever.  I quit reading your drivel after you called me ignorant.

There's nothing wrong with being ignorant; it just means you don't know everything. Everyone is ignorant about something.

 

However, there is something wrong with being ignorant and refusing to learn.

[Kerry.]

.... Thus, there is no place on Earth where WAAS corrections will not improve accuracy ....

 

Fizzy, that is rubbish and talking about learing then it might pay to realize that WAAS used outside the "intended" correction area can/does/will actually make accuarcy worse, in some cases much (much) worse.

 

This is one of the reasons why most manufacturers have now restricted the area where corrections are valid due to the possible cross over between EGNOS and WAAS Geo's.

 

As for this 10 minutes of data every whatever, the "real" WAAS corrections have an error delay of around 6 seconds otherwise I wouldn't like to be on a plane relying on WAAS if it only got an irregular position every so often.

 

One issue is here that very few handhelds actually have the capability to implement WAAS "totally".

 

Cheers, Kerry.

[+fizzymagic]

Really, Kerry? This is rubbish? Can you give an example of a place where a properly-implemented WAAS algorithm would give worse accuracy than none? Don't include Garmin's broken algorithm, please.

 

Remember: there are three WAAS corrections: ionosphere, ephemeris, and clock. The last two do not depend on being anywhere near a ground station. A properly-implemented WAAS correction algorithm will only apply the last two when not near enough to a ionospheric correction point.

 

But if you have some actual evidence that using those corrections out of the WAAS "area" would decrease accuracy, I'd love to see them. Your evidence should include:

• Evidence that forward-corrected ionospheric delay models are worse than uncorrected models over a period of several minutes. (This would mean that solar activity regularly changes by large factors and is reflected in ionospheric changes over short times).
  
• Evidence that corrected ephemeris data is worse than uncorrected ephemeris data over a period of several minutes. (This would imply that either gravity changes or that the density of the upper atmopsphere changes over short periods of time).
  
• Evidence that clock corrections result in decreased accuracy when applied for more than a few seconds. (This would imply that the onboard clocks have short-period fluctuations well outside their design limits).
  or
  
• Evidence that ephemeris or clock data cannot be applied globally. (This would imply that pretty much all of physics is incorrect).
  

If your argument is simply that consumer GPS receivers don't implement WAAS corrections correctly, then please distinguish why this makes WAAS itself useless. Wouldn't it make more sense to blame the receiver than the system?

 

I am certainly willing to admit ignorance if it's appropriate. But nothing I have read about WAAS (and I have read a lot) indicates that it should ever, under any circumstances, lead to a decrease in accuracy unless there is something wrong with the implementation in the receiver. And I consider the problems with Garmin's WAAS implementation "something wrong."

 

In fact, I can come up with a relatively simple implementation concept that illustrates the point nicely. Suppose I have a receiver that implements WAAS corrections properly when the signal is available. That is, it applies all three corrections when in a covered area, but only ephemeris and clock corrections when not. Then, if the signal is unavailable, it applies corrections of the same sign but exponentially-decaying amplitude for a given time, reverting to uncorrected values after that time. That time would be on the order of a few minutes.

 

The only way that such an implementation would give worse accuracy than an uncorrected one would be if during the decay time the corrections changed sign. Given the physical nature of the corrections, such a change is quite unlikely. A fast clock is unlikely to suddenly become slow, a delayed ephemeris unlikely to suddenly become accelerated, and a greater-than-average ionospheric delay is unlikely to suddenly become less-than-average. Thus, this implementation is guaranteed, on average, to have better accuracy than uncorrected measurements.

 

What's wrong with this implementation, in your view?

Edited December 30, 2003 by fizzymagic

[pirlbeck]

I have a Garmin MAP76S......is this the WAAS firmware problem that was referred to above. This is from the Garmin software update site. This is one of the changes made from Vers 3.21 to 3.30

 

" Improved WAAS/EGNOS satellite selection algorithm to select the satellite with the most beneficial corrections given the unit's current position. 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."

 

Does this correct the WAAS problem?

 

Thanks!

[Kerry.]

Fizzy, this example and note that without going into all the little nitty bit and pieces that make it all technical sounding this is what one actually gets in practice, that is everyday use.

 

Haven't really seen a receiver do much different over here, and that includes many different makes and many of these are far and away above recreational receivers.

 

 

But if you've got a receiver that you think will do different then feel free to send it over as Oz is quite a good place to test this type of stuff, probably better reception from POR than even in the US and very much out of the correction area.

 

However one big problem with many manufacturers now is they are shutting the recpetion loophole for units outside the intended ground coverage, guess why?

 

Frankly, if WAAS did it half as well in Oz as you expect it might (and it doesn't) then some certain companies would be pushing there "pin point accuracy stuff" for all it's worth, but they don't, they can't as that's what would be called false advertising and what might even surprise you even more thay actually realize that.

 

Cheers, Kerry.

Edited December 31, 2003 by Kerry.

[+fizzymagic]

What you are seeing here, Kerry, is a well-known problem in which a receiver that is outside the WAAS correction area applies no correction for ionospheric delay, instead of using its normal non-WAAS model. That's a software bug, pure and simple.

 

By the way, the accuracy improvement from the clock and ephemeris corrections is quite modest; I only took issue with your claim that the WAAS system itself was responsible for the decreased accuracy. I am not claiming that WAAS (used properly) will improve position accuracy dramatically in Australia; only that it will improve position accuracy, not degrade it.

 

It turns out that the ionospheric corrections are generated every five minutes; since they are by far the largest component of the WAAS correction, I think a receiver that continues to use WAAS corrections for 10 minutes after the last received WAAS signal is entirely reasonable.

 

What bothers me is that your constant refrain that WAAS hurts accuracy has led many geocachers here in the US to the incorrect belief that the WAAS system itself is flawed. That's simply not true.

 

Given the plot above, I would agree that you should not enable WAAS on your receiver in Australia. And you should complain to the manufacturer about their defective software.

Edited December 31, 2003 by fizzymagic

[+leatherman]

April 2002

I'd like to see an updated graph. The WAAS system wasn't officially activated 'till June or July of 2003.

 

I experienced a dramatic improvement to EPE. Average before was 16'. Now I average as low as 3'.

 

I don't care about the differences between EPE and actual accuracy. My observation was EPE.

[Kerry.]

Fizzy, actually then you'd have to complain to all manufacturers but then apart from any "suspected" issues with software all receivers that come into Oz have WAAS disabled, that simply have to.

 

We've had quite a bit of discussion with some distributors (specifically in the marine field) in Oz about avertising WAAS type systems and their reason? Australian boatbuilders build boats for export, yeah right, so what. Then of course there's they mention MTSAT, yeah sure what about MTSTAT?

 

No really I think people have to take WAAS in their own particular area on face value and base their decisions if it is effective or not on experience. Of course the powers are going to push the virtues of a still yet to be (fully) completed 5-6 billion (US$) system and if it hadn't been at the insistance of the DoT (specifically), it was looking as if the FAA might have kept it in test mode. 5-6 billion is a hell of a lot to justify to congress for a system that only effectively covers CONUS and some fringe areas.

 

Some have to realize that it's not the end and be all of augmentation systems, it has limitations and people do need to realize this.

 

Cheers, Kerry.

Edited December 31, 2003 by Kerry.

[Kerry.]

I'd like to see an updated graph. The WAAS system wasn't officially activated 'till June or July of 2003.

Really about all that changed on July 10, 2003 was a change to message type 2 (normal Geo mode). Apart from including the new GPS launches into the WAAS mask there really wasn't anything done that magically improved operation going from message 0 to 2.

 

Leave the update with me, will have to see who has what available that will fit the purpose.

 

Cheers, Kerry.

[+Sparky-Watts]

Did a side by side test today between my Legend and a friend's Magellan. No noticeable difference in results, both units became incredibly jumpy on accuracy (between 18' and 42') with WAAS on. Turned WAAS off, and both units settled down to between 9' and 13'. Obviously not an inferior software problem with Garmin. Argue all you want, but when I get within 15 to 20 feet of a cache, I want to have a steady reading, and at all points leading up to the cache. With the accuracy jumping all over the place, we couldn't get ourselves within 40 feet of the cache from any direction. Walked the mile back to our vehicles and started over, got within 3 feet of the cache on first attempt. A minute or so of looking and we found it. For me, regardless of any techno-mumbo-jumbo, I'm leaving WAAS off from now on.

 

EDIT: changed distance to direction

Edited December 31, 2003 by Sparky-Watts

[+FarSideX]

I once read an article on the proper use of WAAS. I had it in a file and if I can find it I will make it available.

 

In short it stated the receiver should be left with a constant lock to one of the WAAS sats for 20 mins to 2 hours (I don't recall the exact amount of time) before using it for the 1st time. This did not have to be repeated every time you turned it on. Only if it had been left off for an extended time (a week or month don't remember that either) This allowed it to receive all the longer term data for all the sats.

If this was not done then WAAS could actually degrade the accuracy of the receiver.

 

Before reading and trying this I was not happy with WAAS at all, now I am.

Before

After

 

WAAS does work, just don't turn it on and expect it to start working immediately. This also explains why there is so much disagreement on whether it works or not.

[+Sparky-Watts]

I once read an article on the proper use of WAAS. I had it in a file and if I can find it I will make it available.

 

In short it stated the receiver should be left with a constant lock to one of the WAAS sats for 20 mins to 2 hours (I don't recall the exact amount of time) before using it for the 1st time. This did not have to be repeated every time you turned it on. Only if it had been left off for an extended time (a week or month don't remember that either) This allowed it to receive all the longer term data for all the sats.

If this was not done then WAAS could actually degrade the accuracy of the receiver.

 

Before reading and trying this I was not happy with WAAS at all, now I am.

Before

After

 

WAAS does work, just don't turn it on and expect it to start working immediately. This also explains why there is so much disagreement on whether it works or not.

Hey, I got nothing better to do, I guess I'll try that. Thanks! If it works, it works. If it doesn't, so what, I'm still gonna go caching, right?

[+EraSeek]

Here is the real time WAAS coverage area:

http://www.nstb.tc.faa.gov/vpl.html

 

Fizzymagic is correct that corrections outside the US coverage area can be effectivly applied for better accuracy for those crrections other than the ionospheric corrections. As for ionospheric correction, that is why the modeled corrction area exists. Think of it as a net, that extends from coast to coast. This net is the modeled corrections of ionospheric activity. Your GPS knows where you are and applies the corrections relevent to that section of net regardless of how close to any correction station you are. Basically seen here: http://gpsinformation.net/exe/iono-day.gif

 

(What happens with these ionospheric corrections outside the correction area I assume depends on the firmware in your unit.)

 

First aquisition of WAAS will require patience. About 20 mins. Enable WAAS in an open area with exposure to the SW and SE. After augumentation flags "w's" appear on your sat bars, you may see the accruacy reading go way up, then drop down. This reading does not mean a lot, ever. Mostly just says how it thinks your unit is doing. It is NOT your true accuracy. After you once have acquired WAAS, the next time you use it it will only take a few minutes as long as you have the WAAS sats in view.

 

My 2bits.

[+Sparky-Watts]

)

 

First aquisition of WAAS will require patience. About 20 mins. Enable WAAS in an open area with exposure to the SW and SE. After augumentation flags "w's" appear on your sat bars, you may see the accruacy reading go way up, then drop down. This reading does not mean a lot, ever. Mostly just says how it thinks your unit is doing. It is NOT your true accuracy. After you once have acquired WAAS, the next time you use it it will only take a few minutes as long as you have the WAAS sats in view.

 

My 2bits.

So, after the first initialization, will accuracy reading on the unit still go really high and drop back down each time you use it? Will the accuracy reading ever stay on the lower end after jumping way up, or will it continue to jump up and down?

[+shunra]

First aquisition of WAAS will require patience. About 20 mins. Enable WAAS in an open area with exposure to the SW and SE. After augumentation flags "w's" appear on your sat bars, you may see the accuracy reading go way up, then drop down. This reading does not mean a lot, ever. Mostly just says how it thinks your unit is doing. It is NOT your true accuracy. After you once have acquired WAAS, the next time you use it it will only take a few minutes as long as you have the WAAS sats in view.

Thanks, EraSeek!

Is that the first 20 minutes of using WAAS ever, or the first 20 minutes in a certain area, or the first 20 minutes of WAAS use on a specific trip?

 

Today I cached without WAAS, and I had stable readings, down to one digit number of feet from a cache, and no jumps. I now understand that my use of "uninitialized" WAAS was the reason for the jumpiness last time. On my next trip, I''ll initialize it as you say, and check out the difference.

 

When caching, do you have WAAS on all the time, or only near the cache, where accuracy really matters?

[LowranceTracker1]

WAAS is Inferior to DGPS for geocaching.

 

WAAS is limited by geosyncronous sattelites in orbit around the equator.

 

WAAS was created for airplane use, above 2000 feet, not ground level users.

 

WAAS is affected by Solar Storms, just as regular GPS signals are, whereas DGPS is not and will continue to correct signals.

 

I'm not sold on WAAS. It is in it's infancy, and until it is grown up and a fully operational system, it's being touted to ground level GPS is more or less a scam capitolized by GPS companies to sell more product.

 

Side by side:

 

I went on a geocache with a non-WAAS GPS (My Lowrance GM100) with another geocacher who was using a Garmin 76S with WAAS, and an external antenna. In all cases, my unit was as accurate, or more accurate than his was.

[+EraSeek]

WAAS is Inferior to DGPS for geocaching.

 

WAAS is limited by geosyncronous sattelites in orbit around the equator.

 

WAAS was created for airplane use, above 2000 feet, not ground level users.

 

WAAS is affected by Solar Storms, just as regular GPS signals are, whereas DGPS is not and will continue to correct signals.

 

I'm not sold on WAAS. It is in it's infancy, and until it is grown up and a fully operational system, it's being touted to ground level GPS is more or less a scam capitolized by GPS companies to sell more product.

 

Side by side:

 

I went on a geocache with a non-WAAS GPS (My Lowrance GM100) with another geocacher who was using a Garmin 76S with WAAS, and an external antenna. In all cases, my unit was as accurate, or more accurate than his was.

That is only the first time you initialize it. After that it should come up easily when in view. It does take 12 mins for the full almanac to downloawn from the sats so for best results wait for 12 mins of use before marking a cache. But this is true even when not using WAAS.

 

As for Lowrance tracker, you are simply not correct!

DGPS is inferior because it is highly dependant on how close to a transmitting station you are. The further away, the further off your correction will be. WAAS is the solution to this.

 

So how is WAAS limited by sattelites which cover the US? I'm in Northern Washington state and get both WAAS sat just fine. The only limiting factor is that they need another or two backup sats, and a little higher so they are easier to get. They do have plans to addd more soon.

 

"WAAS was created for airplane use, above 2000 feet, not ground level users" If you read the official sites you will see that WAAS functions for land based users as well just fine. Also WAAS is in use for aviation approuches down to, I believe, 300' now.

 

"WAAS is affected by Solar Storms, just as regular GPS signals are, whereas DGPS is not and will continue to correct signals."

The whole idea of WAAS is to correct for things like a charged ionosphere which causes signal delay. With DGPS it only corrects well if you are very close to the station. The further away and worse the storm, the worse your correction. Not so with WAAS.

 

WAAS is fully operational. Listen, WAAS is not going to make a huge difference to us anyway. If you don't like it, don't use it! Personally, I do like it. Why not take advantage of the technology?

 

When do I use it? Most of the time. When I know i can get the sats. When planting a cache. When I go into thick tree cover or a canyon, I geneally turn it off.

 

My Advice: Go stand on a benchmark, (a known coordinate) in an open location, set the benchmark as your GOTO target. Stand on the benchmark with WAAS on, then with WAAS off. See what you think.

[+PDOP's]

When do I use it? Most of the time. When I know i can get the sats. When planting a cache. When I go into thick tree cover or a canyon, I geneally turn it off.

 

My Advice: Go stand on a benchmark, (a known coordinate) in an open location, set the benchmark as your GOTO target. Stand on the benchmark with WAAS on, then with WAAS off. See what you think.

I think you're right with these two statements. WAAS use should be based on the users individual conditions (topography vs reception of WAAS sats). The only accuracy claims that matter are those for known positions (benchmarks).

[+blindleader]

WAAS is Inferior to DGPS for geocaching.

Who, besides a few who happen to have it for business, and those with way too much money, uses DGPS for geocaching?

 

WAAS is limited by geosyncronous sattelites [sic] in orbit around the equator.

Wish I knew what this means. WAAS is also "limited" by ground reference stations. Are you comparing it to DGPS, which has similar "limitations".

 

WAAS was created for airplane use, above 2000 feet, not ground level users.

I think you misplaced a decimal point there. Navstar itself (most people call it GPS) was not created for a lot of things that it is used for now, including geocaching.

 

Oh, that's enough. What does DGPS have to do with this thread, anyway?

Edited January 1, 2004 by blindleader

[+EraSeek]

By the way, here is the error chart

 

Error Value :

Ionosphere 4.0 meters

Clock 2.1 meters

Ephemeris 2.1 meters

Troposphere 0.7 meters

Receiver 0.5 meters

Multipath 1.0 meter

Total 10.4 meters

 

I believe only the last two are not corrected by WAAS.

[+fizzymagic]

There have been a couple of misconceptions about WAAS that have crept into this discussion.

 

First, the idea that WAAS was designed to be only useful for airplance navigation is nonsense. The system was deigned to meet the stringent requirements of airplane navigation, but those are incredibly demanding requirements; in actual fact, meeting those requirements makes WAAS a broadly useful system.

 

In particular, one feature that WAAS has that DGPS does not is that WAAS is designed to provide not just corrections, but safe corrections. It sends a guarantee of how "good" the corrections are. The design prevents so-called Hazardous or Misleading Information (HMI). For example, if the WAAS system detects an ionospheric storm, it automatically changes the reliability reported for the ionospheric corrections so that receivers can adjust their accuracy estimates accordingly.

 

There are two kinds of WAAS corrections: fast and slow. Fast corrections were originally intended mainly to compensate for Selective Availability (SA), but that was turned off, so the fast corrections don't really do much any more. The slow corrections are updated only every 5 minutes or so (I'm still trying to find the exact details).

 

I've been thinking about the "jumping around" behavior that several people in this thread have attributed to WAAS. The only way that tha WAAS system itself could generate such behavior would be by means of those fast corrections. But those tend to be very small, so I doubt they are the origin of the effect. More likely is that not enough WAAS information has been downloaded to use all the satellites, so the GPS receiver decides to use only a few satellites, with the attendant high position noise.

 

My advice to those who experience this behavior: Make sure your WAAS system is fully initialized (decent view of WAAS satellites for 10 minutes) and that you have installed the newest firmware for your receiver.

[+Stunod]

The only limiting factor is that they need another or two backup sats, and a little higher so they are easier to get. They do have plans to addd more soon.

I think Johann Kepler and Sir Issac Newton proved you can’t put the sats in a higher geosynchronous orbit. In order for them to remain in a constant position in the sky, they must be in orbit over the equator at about 22,250 miles up.

Edited January 2, 2004 by Stunod

[+Lil Devil]

Why do the WAAS sats need to be in geosynchronous orbit?

[+EraSeek]

The only limiting factor is that they need another or two backup sats, and a little higher so they are easier to get. They do have plans to addd more soon.

I think Johann Kepler and Sir Issac Newton proved you can’t put the sats in a higher geosynchronous orbit. In order for them to remain in a constant position in the sky, they must be in orbit over the equator at about 22,250 miles up.

Yes you must be right. Looks like just additional sats.

Here's what they are planning: http://gps.faa.gov/CapHill/geosat.htm

[+PDOP's]

Why do the WAAS sats need to be in geosynchronous orbit?

Good point. Actually when you think about it it would be much better if the corrections were broadcast from the regular GPS sats which would eliminate the reception problems with geostationary orbit. I know that's not possible with the existing sats but maybe with future generations?

 

I think that the geostationary communications satellites were used because of their availability and economics. An interesting fact " A single geostationary satellite can see 42 percent of the earth's surface and a constellation of 3 satellites can see all of the earth's surface between 81° S and 81° N. "

Edited January 2, 2004 by PDOP's

[+W7WT]

Shunra, I live just south of you in Bremerton, Washington and have been using the 76S since it first came out. Before that I used the MAP 330. At first I kept going back and using the 330 because I wasn't that familiar with my new 76S. Once I got familiar with it it is a great GPS. One thing for sure, you are one of the MOST active Geocacher in this area. Welcome Aboard. Dick, W7WT BTW if you ever do the caches at Howe Farm, you can get great WAAS coverage there. (NOT IN THE TREES!!}

[+shunra]

Shunra, I live just south of you in Bremerton, Washington and have been using the 76S since it first came out. Before that I used the MAP 330. At first I kept going back and using the 330 because I wasn't that familiar with my new 76S. Once I got familiar with it it is a great GPS. One thing for sure, you are one of the MOST active Geocacher in this area. Welcome Aboard. Dick, W7WT BTW if you ever do the caches at Howe Farm, you can get great WAAS coverage there. (NOT IN THE TREES!!}

Thanks for that most personal welcome! I look forward to an opportunity for making it down to Bremerton, and I'll keep the Howe Farm caches in mind.

I am well aware of the enormous advantages the 76S has over the Magellan Blazer 12, which I used before. Having started out with my 'career' with a B12, I don't stop marvelling at the versatility of the 76S. I'm still learning about it!

If there is anything between Bremerton and the Hood Canal Bridge that you'd like to do this weekend, let me know. Chances are that I haven't done it yet, and perhaps we can team up. So far, most of my hikes have been solo

Glad to be in touch!

[Kerry.]

.... In particular, one feature that WAAS has that DGPS does not is that WAAS is designed to provide not just corrections, but safe corrections.  It sends a guarantee of how "good" the corrections are ....

Fizzy, one would have thought that's what differential systems are supposed to do, detect the problems, lets face it both are differential systems and both are supposed to eliminate the bad data, that's what they do.

 

Which recreational receivers have the capability of using all the error capabilities and alarms?

 

Cheers, Kerry.

Edited January 2, 2004 by Kerry.

[kmshuey]

I have an eTrex Venture, which I belive was one of the first GPSr to have WAAS. I have noticed I get the same or worse accuracy when WAAS is enabled. Reading over the postings, I conclude the reasons it could be is this:

 

A- I have one of those "early Garmin WAAS defects" or

B- I am not letting the WAAS get enabled corectly by letting it sun tan for an hour and make friends with a WAAS satelite. Can someone tell me if they know for a fact the Venture was bad WAAS?

 

I suppose I will test theory B out myself soon enough.

Can't wait till I get enough $ to upgrade. Thinking Legend or Rhino. Maps is a must, but the communications on the Rhino seems cool too. Topograhical maps would be even better, but can I get all that affordably?

[+GeckoGeek]

Can someone tell me if they know for a fact the Venture was bad WAAS?

Have you tried updating the firmware?

[gilbertf]

I'm located near Paris in France and using WAAS is not very easy especially in urban zones. The satellite that covers most part of Europe is called AOR-E I think, and checking on the map I see that it's located south of Paris and if I orient the GPS to the south, it grabs the WAAS satellites but I lost it pretty soon as I move around. I usually don't get a clear view of the south sky unless I get out of urban areas. I keep it off now, unless I really end up in a rural place with no buildings on south.

[+blindleader]

Why do the WAAS sats need to be in geosynchronous orbit?

 

They don't have to be, but geosynchronous orbit is where you put communications satellites. With just two, eventually three, such transmitters, you cover all of North America. If the Navstar satellites were to provide their own correction data you'd have to redesign them so that every one of them carried the appropriate transmitter. Just in case anyone is fuzzy about the concept of WAAS (can you imagine?), there really isn't such thing as a WAAS satellite. The so-called WAAS satellites are not involved in the measurement/correction process but are simply communications platforms that transmit correction information to the GPS receivers. They were not launched by, nor are they owned by the FAA, which leases the services from their owners. Of course that can change and I'm not sure if the FAA plans on making the third satellite their own.

[LowranceTracker1]

(fizzymagic @ Jan 1 2004, 05:17 PM)

.... In particular, one feature that WAAS has that DGPS does not is that WAAS is designed to provide not just corrections, but safe corrections.  It sends a guarantee of how "good" the corrections are .... 

 

So the DGPS system used for sending accurate signals to our Coast Guard is not accurate eh? Fizzy, I think you're full of yourself dude.

 

As far as someone stating that you have to be "Really close" to a DGPS station to get the corrections, I must say this... 200 miles is really close? I have seen people test their new DGPS antenna on their GPS and receive up to the second corrections from this kind of distance. I think since there are DGPS beacons all over the USA that it's not a problem to get a signal. Land Surveyers use DGPS, Water companies use DGPS, the United States Military uses DGPS.

 

What does DGPS have to do with this thread? It has to do with accuracy and dependability. WAAS is not the only accuracy enhancing feature for GPS, and I wanted to make that clear.

 

I say WAAS is still a bad idea, and I don't buy all the hype.

[Kerry.]

.... Just in case anyone is fuzzy about the concept of WAAS (can you imagine?), there really isn't such thing as a WAAS satellite. The so-called WAAS satellites are not involved in the measurement/correction process but are simply communications platforms that transmit correction information to the GPS receivers.

Actually I can imagine, the WAAS Geo's can in fact be included in the determination of the position solution and can basically mirror the measurement function similar to a GPS satellite but more like a pseudo satellite.

 

This is a WAAS option, does exist but hasn't seen a lot of activation in everyday useage.

 

Cheers, Kerry.

[+EraSeek]

(fizzymagic @ Jan 1 2004, 05:17 PM)

.... In particular, one feature that WAAS has that DGPS does not is that WAAS is designed to provide not just corrections, but safe corrections.  It sends a guarantee of how "good" the corrections are .... 

 

So the DGPS system used for sending accurate signals to our Coast Guard is not accurate eh? Fizzy, I think you're full of yourself dude.

 

As far as someone stating that you have to be "Really close" to a DGPS station to get the corrections, I must say this... 200 miles is really close? I have seen people test their new DGPS antenna on their GPS and receive up to the second corrections from this kind of distance. I think since there are DGPS beacons all over the USA that it's not a problem to get a signal. Land Surveyers use DGPS, Water companies use DGPS, the United States Military uses DGPS.

 

What does DGPS have to do with this thread? It has to do with accuracy and dependability. WAAS is not the only accuracy enhancing feature for GPS, and I wanted to make that clear.

 

I say WAAS is still a bad idea, and I don't buy all the hype.

"Additionally, WAAS provides indications to GPS/WAAS receivers of where the GPS system is unusable due to system errors or other effects. Further, the WAAS system was designed to the strictest of safety standards – users are notified within six seconds of any issuance of hazardously misleading information that would cause an error in the GPS position estimate."

 

It is a safer system.

 

 

"As far as someone stating that you have to be "Really close" to a DGPS station to get the corrections, I must say this... 200 miles is really close? I have seen people test their new DGPS antenna on their GPS and receive up to the second corrections from this kind of distance. I think since there are DGPS beacons all over the USA that it's not a problem to get a signal. Land Surveyers use DGPS, Water companies use DGPS, the United States Military uses DGPS. "

 

The fact is, the further away from a DGPS station you are, the less correct the corrections will be. MUCH less so than with WAAS. The reason is that with DGPS you are getting corrections for the stations location, not the GPS's location. No, in many cases the difference will not be that great, but in harsh conditions, larger ionosphere disturbances it WILL be that great. My guess is that 200 miles here will make a huge difference. WAAS is more accurate and reliable (with the exception of the fact that if they lose a WAAS sat they are up a creek). (AND yes, even they call them WAAS sats.)

 

"WAAS Geostationary Satellites (GEOSAT)

The current WAAS geostationary communications satellite (GEOSAT) constellation consists of two Inmarsat-3 satellites, leased through September 2006. The non-optimal coverage area provided by these satellites result in a potential single thread of failure for the entire WAAS system in the eastern four-fifths of the CONUS. (The 2 Inmarsat satellites are equivalent to one optimally placed satellite between the orbital slots of 119 and 129 degrees West.)"

 

 

"WAAS is not the only accuracy enhancing feature for GPS, and I wanted to make that clear."

 

Quite correct.

Edited January 15, 2004 by EraSeek

[+GeckoGeek]

(fizzymagic @ Jan 1 2004, 05:17 PM)

.... In particular, one feature that WAAS has that DGPS does not is that WAAS is designed to provide not just corrections, but safe corrections.  It sends a guarantee of how "good" the corrections are .... 

 

So the DGPS system used for sending accurate signals to our Coast Guard is not accurate eh?

No, he didn't make any statements of accuracy in that quoteback - he was pointing out that it does come with extra protection against creating problems if things should go wrong. And somewhere, sometime, they DO go wrong. And when that happens, somewhere there will be an airplane trying to land. You want something that will turn on the light and say "error" and not just feed you bad readings causing you to land on the grass strip instead of the runway.

[+fizzymagic]

So the DGPS system used for sending accurate signals to our Coast Guard is not accurate eh? Fizzy, I think you're full of yourself dude.

I may well be full of myself; however, I didn't say that WAAS is more accurate than DGPS; I was simply pointing out the errors in your post that claimed that DGPS is better than WAAS.

 

Do you really take a handheld DGPS system out with you when you go geocaching?

[Kerry.]

.... strictest of safety standards – users are notified within six seconds ....

 

6 seconds Yes, very tight but very few receivers yet have certification to meet this requirement and certainly not any of the recreational handhelds.

 

I suppose one could say with dGPS that erroneous satelitte gets trapped even before transmission.

 

.... the further away from a DGPS station you are, the less correct the corrections will be ....

comes down to about 1 metre per 150 miles (from memory)

 

.... if they lose a WAAS sat they are up a creek ....[/quoute]

 

Up the creek big big time right now and something that is absolutely worrying for a 5-6 billion $$ system, a real bottleneck.

 

Cheers, Kerry.