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WAAS...do You Really Need It?


OKThumper

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I just came across a document published by the Colorado Division of Water Resources, concerning accuracies of GPS data.  Field testing was conducted by the Division using GPSr that used averaging vs. units that used WAAS.  The purpose was to determine whether the division would accept positional data for water well locations derived from GPS as opposed to surveyed from benchmarks.  The following was a quote from this article that summarizes their findings.

 

"Field testing by the Division of Water Resources of inexpensive 'averaging' GPS units has yielded point position data within a few tens of meters of benchmark surveyed positions.  A map plotting and review of data can provide "map corrected" averaged GPS data of good (10-20 meter ranges) quality.  By comparison a WAAS enabled GPS unit with averaged position information can attain accuracies of 1-3 meters of benchmark locations."

 

So this government agency did find accurracies that were an order of magnitude greater with the WAAS enabled then without it.

 

Reference:  Article name: "Why Not GPS?" by Chuck Roberts.  Contact Glenn Graham at the Colorado Division of Water Resourses, for copies of the article or field test or general info at 303-866-3581 x8270

 

As far as I know none of this data is available online.

Did they actually *test* WAAS receivers against non-WAAS?

 

From the way I read that quote, it sounds like they tested non-WAAS receivers. Their "corrected" data of 10-20 meters doesn't sound too far afield from the typical 15 meters cited. So that part sounds legit.

 

But the last sentence sounds just like an FYI that WAAS can improve accuracy. It doesn't seem to imply they actually tested WAAS vs non-WAAS receivers to me.

 

In the test my son and I are currently doing, we're not seeing positioning data more than 3 meters difference between WAAS and non-WAAS. Usually it seems more like 2 meters.

 

The final results aren't in yet, but the simple yellow eTrex (non-WAAS) seems to be holding its own pretty well against its bigger WAAS-enabled brother (a Vista).

 

George

Edited by nincehelser
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The GPS also uses your initial point,when you 1st initialize it to calculate your position on the Earth,If this BM was my Initialization Point and the control that I am using,then the Satts are still using that same position ....

 

Yeah right

 

But like I have heard alot of (Who are you)???What are your credintials?

You don't know what you are talking about.

 

Yeah right

 

Geo, are you going to start all this waffle again :)

 

Cheers, Kerry.

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But the last sentence sounds just like an FYI that WAAS can improve accuracy. It doesn't seem to imply they actually tested WAAS vs non-WAAS receivers to me.

Same here with the "typical" can attain accuracies of 1-3 meters. Especially when inexpensive 'averaging' GPS units actually have some general precision issues displaying less than 3 metres. Again many quote GPS accuracy as X metres but forget the important bit, the type/confidence of those metres.

 

Cheers, Kerry.

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Sorry off topic.

end.

Why haven't you showed that pretty plot in GPS Software forums on WASS Averaging?

That would explain a little more here Kerry.

Geo, Don't think that plot has much to do with WAAS accuracy but more to do with the "affect of WAAS on accuracy" when WAAS is enabled outside the intended ground coverage area.

 

Cheers, Kerry.

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Same here with the "typical" can attain accuracies of 1-3 meters. Especially when inexpensive 'averaging' GPS units actually have some general precision issues displaying less than 3 metres. Again many quote GPS accuracy as X metres but forget the important bit, the type/confidence of those metres.

Here's where I'm getting confused.

 

Do the Garmins do any kind of position averaging if you just let them sit in one location for a while (like I'm doing in this test)? I was under the impression that they don't, but Magellans do. I'm just trying to figure out why the readings are so close to each other...I just expected the non-WAAS readings to be more spread out than I'm getting.

 

And the figure the Garmins display ("Ready to navigate to X meters"). Am I correct in thinking this is like a "confidence" reading, or is it really something else?

 

Elevation is another thing. The Vista seems to vary a lot more than the eTrex yellow. I'm thinking this may have something to do with the Vista's barometer, but any attempts to disable it have met with really strange readings. The between the two units the elevation readings seem to be close most of the time, but the Vista seems prone to wider swings.

 

Thanks

George

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heres a stupid newbe Q,

whats waas? thanks :) TAZ

If memory serves, it stands Wide Area Augmentation Service.

 

It's a system that works over much of North America, and it's intended purpose seems to be to make GPS readings more accurate for aviation use, especially in the elevation readings. It's pretty much standard now in most consumer GPS receivers. The only one that I can think of on the market that doesn't have it is the original yellow eTrex.

 

There have been debates here regarding the utility of WAAS. My son and I are now doing an experiment to see how WAAS really performs with regards to consumer hand-held units.

 

So far I'm just getting more confused. Regular GPS seems to be a lot better than I expected, and WAAS seems to be kind of touchy...even out in the open where it should have no problems. It could be the firmware in my Vista is still buggy with regards to WAAS. I'm still trying to figure that one out.

 

George

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Do the Garmins do any kind of position averaging if you just let them sit in one location for a while (like I'm doing in this test)?  I was under the impression that they don't, but Magellans do.  I'm just trying to figure out why the readings are so close to each other...I just expected the non-WAAS readings to be more spread out than I'm getting.

 

And the figure the Garmins display ("Ready to navigate to X meters").  Am I correct in thinking this is like a "confidence" reading, or is it really something else?

George, some Garmin models can/do average but it's not like the fixed auto-averaging that Magellan uses.

 

The Yellow and Vista I don't think has averaging but this might depend on software upgrades as I am aware of some Garmins that in recent time have been burdened with Auto type averaging. Units like the GPS48 has a manual averaging function prior to saving.

 

This "confidence" reading, just an estimate, simply can't be anything more than that.

 

As for the "closeness" of the readings? you might find some differences (if one could call them that) if you were recording the output from each unit, which might havve better precision than what is displayed on the screen. However doing that is not really meeting the practical side of everyday use, is it.

 

Cheers, Kerry.

Edited by Kerry.
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The issues with using WAAS have much more to do with hiding a cache than with finding it. When I hide a cache, I feel obligated to provide the best coordinates I can. So I do several things to maximize my accuracy. Using WAAS properly is one of those things.

 

I don't think WAAS is necessary to find most caches. There are some exceptions for which it has been helpful, but for the most part it doesn't make a huge difference in my ability to locate the cache container.

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WAAS is not 'necessary' but is nice to have. Those that claim the accuracy is not improved have not taken the time to use it properly. (It takes at least 20 minutes for the receiver to collect all the data required)

 

How close your receiver gets you to a cache is not a good test of it's accuracy unless you believe everyone else's receiver is more accurate than yours.

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Do you need it? No.

 

Do you want it? Yes, see Eraseek’s post.

 

This is how I understand it works: The ground station, being attached firmly to the earth, knows it is located at N XX° XX.XXX W YYY° YY.YYY. It is equipped with a GPS receiver, the satellite tells it, “No, you’re over there next to the little hill.”

 

The station doesn’t believe this though, “I know where I am, so screw you.” The ground station then sends a signal back to the satellite, either #35 or #47, that contains the correction difference. The station tells the satellite, “OK listen, we have to work out our differences for the betterment of our creators. You think I’m over there, but I cannot move. So please adjust your signal to show me over here instead of over there.”

 

The satellite responds, “Oh you’re such a b1tch! The power company called and wants you to turn down the flame just a bit. And by the way, who dressed you this morning? That color is simply awful on you. It’s the atmosphere honey; it’s totally delaying my signal. If you would clean up some of that dust down there maybe this wouldn’t happen. OK, OK, I’ll make the adjustment.”

 

You and I don’t see this electronic bickering, but the same correction that was applied to show the ground station in the correct position is also applied to your position. Thus, you are probably closer to the true lat/long with WAAS on than off.

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Hey Thumper,

 

I noticed you kind of breathing a sigh of 'Why did I start this topic?'

Down at the bottom left of the webpage, you can choose from your moderator's

drop down menu to close the topic.

(Not that I'm saying you should or anything.)

It's what the forum calls 'self moderation'.

You can close any topic you open.

Just so you know.

:)

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Did they actually *test* WAAS receivers against non-WAAS? 

 

From the way I read that quote, it sounds like they tested non-WAAS receivers.  Their "corrected" data of 10-20 meters doesn't sound too far afield from the typical 15 meters cited.  So that part sounds legit.

 

But the last sentence sounds just like an FYI that WAAS can improve accuracy.  It doesn't seem to imply they actually tested WAAS vs non-WAAS receivers to me.

 

I don't know if they tested both units. I am assuming that they did based on information that division has released during classes, seminars, and presentations about using GPS. However, you are correct that the wording in the quote I posted could be interpreted as not having actually tested a WAAS unit.

 

I found this: Board Bullitin 2000-1, which is an older version of the document that I quoted. In this linked version there is no mention of WAAS, but it does reference the test of "inexpensive 'averaging' units". I would infer from that that your presumption is correct and WAAS units were not tested.

Edited by jfegel
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The Theory is based on the Universe as a Mathmatical Whole,held together in a precise order and time,

which in turn creates the 360 degrees in a Circle,Year(Biblical) not (Julian),24 divisions of the 360,then the 7 divisions,notes,colors,scale,techtonic plates..............Well the more you look the more you find how this is done Which goes back to Einstiens E=MC2 the Energy inherent in all matter....are all linked to Electricity and magnetism,and all types of radiation are the same things just a diffrent frequency and vibration,which in turn goes back to the Ancient Philosophers.

:D Wow. I thought this was the "Getting Started" forum. :D

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crzycrzy: thanks for the option. But I have gleaned a little bit of knowledge by reading the posts. I have applied a small amount of "huh" to some of it and a lot of "huh" to a lot of it, but still have picked up some good points. Besides as I said in another post I am not the only person that is reading these post, maybe they are also getting a little out of it. If it remains friendly and informitive I will let it run its course. I appreciate all those that have put effort into answering this for me......and others.

 

Thumper :blink::):)

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Just to reiterate FizzyMagic's comment, 'cause to me it's the most important...

 

WAAS is most useful for hiding caches, NOT finding caches.

 

If the hider wasn't using a WAAS enabled unit properly, someone searching with such a GPS could be drawn to an inaccurate location!

 

All my finds are via a basic eTrex. All my hides have coords averaged over multiple days. My couple pending not-founds were not due to coord problems but red-herring or lack of information issues.

 

That said, my night-caching buddy has WAAS enabled and we split the first finds 50/50. (Amusingly, often the one who finds most the stages of a multi first isn't the one to find the final stage first.)

 

As for George's experiment/test, remember the probability of being off is not linearly distributed! (More like a bell curve.) Hence the reason averaging is so useful. If one in ten readings are aberrant, it effectively dissappears. So WAAS only truely makes a difference a very tiny percentage of the time. (Careful, or I'll provide the link to the thread with all my charts and graphs! Heh..)

 

Enjoy,

 

Randy

 

PS: After enquiring of several WAAS users at an event last Summer, I found most weren't even sure if it was enabled!

 

PPS: At the same event, we held an accuracy test at a GPS-verified benchmark--only a basic eTrex nailed it.

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Well, my laptop literally burned up doing the calculations, but I think it had more to do with the fan going out.

 

Long story short...we took 20 readings at the same, very open location at various times over three days. WAAS and non-WAAS readings had an average difference of 1.6 meters, or roughly 5 feet.

 

The most extreme difference was 3.6 meters, which happened twice. However, 5 times there was no difference measured at all.

 

My interpretation is that regular GPS service worked a lot better than I expected. Granted, it's a small sampling, but 25% of the time WAAS and non-WAAS measured the same, 10% of the time they differed by about 11 feet. On average they only differed by 5 feet. That doesn't seem like a huge difference to me, especially for something like hiking or geocaching.

 

We measured elevation, but I haven't much confidence in that data. I think the Vista's barometer impacted the measurements.

 

Please realize that we just measured the differences between the readings of a WAAS and non-WAAS receivers. We didn't compare them to a measured point like a benchmark.

 

George

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nincehelser: Call me simple if you want but I understood all of your post, and it seems to confirm what most if not all of the math whizes and research guys have said. Which is a GPSr with or without WAAS will work just fine for or hobby/sport. Therefore, if you have a GPSr without WAAS you will be about as likly to be within the "put your GPSr away and use your eyes" range as you would be if it did have WAAS. In addition, you do not need to sell your GPSr and upgrade to one with WAAS, unless you are ready for an upgrade due to the age or useablility of your present GPSr, and just want a GPSr with other goodies and just happens to have WAAS. I better quit now before I confuse myself again, beside here comes the guys with my white jacket and medications.

 

Thumper :ph34r::P:ph34r:

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GPS was originally designed to work without WAAS. WAAS corrects for situations that may or may be present at the time you are using your receiver. Comparing a WAAS enabled receiver to a non-WAAS one should give little or no difference most of the time. The WAAS enabled receiver should show a better EPE as it has more information then the other to base that on, but if there are no corrections or very little correction being made both should show you are in the same location.

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nincehelser: Call me simple if you want but I understood all of your post, and it seems to confirm what most if not all of the math whizes and research guys have said. Which is a GPSr with or without WAAS will work just fine for or hobby/sport. Therefore, if you have a GPSr without WAAS you will be about as likly to be within the "put your GPSr away and use your eyes" range as you would be if it did have WAAS. In addition, you do not need to sell your GPSr and upgrade to one with WAAS, unless you are ready for an upgrade due to the age or useablility of your present GPSr, and just want a GPSr with other goodies and just happens to have WAAS. I better quit now before I confuse myself again, beside here comes the guys with my white jacket and medications.

 

Thumper :ph34r::P:ph34r:

Yes, that's in line with what I'm thinking.

 

DOH! I just noticed an error in the spreadsheet! Forget what I said. I'm going to have to recalculate.

 

George

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OK. Fixed the spreadsheet.

 

Average difference between readings: 1.9 meters, or about 6 feet.

 

Most extreme difference: 3.6 meters, which happened twice, 10% of the time.

 

They only measured *exactly* the same once, or 5% of the time.

 

Looking at it another way:

 

0.0 meter difference: 5%

1.0 meter difference: 15%

1.4 meter difference: 20%

2.0 meter difference: 25%

2.2 meter difference: 20%

2.8 meter difference: 5%

3.6 meter difference: 10%

 

I still stand by my original conclusion, but obviously the receivers didn't measure exactly the same as often as I originally calculated.

 

Another way to look at is the receivers were in agreement within 7 feet 85% of the time.

 

George

Edited by nincehelser
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Looking at it another way:

 

0.0 meter difference: 5%

1.0 meter difference: 15%

1.4 meter difference: 20%

2.0 meter difference: 25%

2.2 meter difference: 20%

2.8 meter difference: 5%

3.6 meter difference: 10%

How did you measure such small distances? My understanding is that the Lat/Lon reading of handhelp GPS units only goes down to about 6 feet or so. Did you input a coordinate and then see how far away it said you were?

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I use WAAS when using my V in the car but when it is combined with heavy treee cover and bad reception, it seems to throw my reciever off more. It is at least useful in open areas or cars, mine does great with external antenna in thte car. Sometimes I use it caching, but it seems to work better in the woods without it.

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Just the difference the #'s were making.

 

O.K.

 

Try using a Control Grid.

A point to point measure to,or go to from a controlled reading or point within the grid.

 

If you watch closely when you get 2 GPS recievers real close together the readings fluctuate more..observation.

Try it with 1 unit at different times from same points.(Less battery useage)

 

You will be truly amazed at your outcome and it will boost your confidence in the systems more.

 

Or that may be too much work fur ya...Whatever u think.

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Science

1.The state or fact of Knowledge,2. systematized knowledge derived from observation or study,and experimentation carried out in order to determine the nature or principals of what is being studied. 3. a branch of knowledge or study,esp. one concerned with establishing and systemizing facts,principals,and methods,as by experiments and hypotheses [the science of mathmatics].

 

Algebra and Boolean expressions

 

Variables

click on update

 

Engineer

1.[NOW RARE] a person who makes engines.

 

ENGINEERING

the science concerned with putting scientific knowledge to practical use,divided into the various branches.

 

How do you calculate the true trajectory :D of your rocket there without some kind of control.

as big as it is :lol: you better know where it is going :P and where to find it. :rolleyes:

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At one point there I was in the Top 10% of the Entire U.S in Mathmatics I think I am still up there somewhere,and I have had several years of Formal Education since then.

 

I am just looking for the practical applications of your data.

 

and something to base it on.

 

If you look at my caches you will see some intriguing Mathmatics, Science and Engineering that went int them.To most they are just another plot of caches.

 

I have been working at several aspects of this for well over 20 years now,I am no rocket scientist,but I do have a good handle on the technology, as I have updated it from the very beginnings of this all.

 

I did not want to stir anything up it is just that greater things could be realized if correctly and scientifically done.

 

I am REALLY into Engineering and Science and Art and Math and Anything that has to do with the Mere existance of us humans here on this Planet and in the Universe.

 

Gee I watch NASA TV just about every day.dosen't that count fur sumpin.

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At one point there I was in the Top 10% of the Entire U.S in Mathmatics I think I am still up there somewhere,and I have had several years of Formal Education since then.

That just goes to show..."the top 10% of the Entire U.S. in Mathmatics" is a group of about 30 million people. Wow. Incredibly impressive.

 

George

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I was wondering the same thing about WAAS capabilities (I also have the eTrex). Last week, I went geocaching with a buddy of mine (he has the SporTrak Map - WAAS capable). I found that the readings were almost exactly the same, and it seems that either a) WAAS isn't great or :P the eTrex has something like WAAS that isn't. Either way, I hope that helps - I would save your money and wait until you upgrade for lots of new features.

 

~Jared

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This is so cool, a boxing match with no blood. Just kidding. I agree that it seems we have determined the WAAS is not now at it's full potential, maybe in the future it will be there. Then most of this will just be academic (dang it you guys made me look up a big word).

 

Thumper :P;):P

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I have an etrex Venture and today I had a good lock on all 12 of the satellites visible (which had never happened before!). I had an EPE of 9 feet under a tree! It zeroed out with this 9 ft EPE and WAAS enabled. I didn't find the cache though! It's there. Someone found it a few days ago and there is a spoiler picture of it on the web page. I'll have to go back and get it.

Edited by Wacka
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Sorry. It wasn't necessary for the purposes of this test.

 

I'll stick with real science and engineering if you don't mind.

 

George

I will just ask very simple then.

 

1.What is the scientific use of your test?

 

2.What is it's practical use.?

 

3.What is it based on?

 

4.And where is the RUBBISH ?

 

Here is your life jacket.

Is there anything else?

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Sorry.  It wasn't necessary for the purposes of this test. 

 

I'll stick with real science and engineering if you don't mind.

 

George

I will just ask very simple then.

 

1.What is the scientific use of your test?

 

2.What is it's practical use.?

 

3.What is it based on?

 

4.And where is the RUBBISH ?

 

Here is your life jacket.

Is there anything else?

>1. What is the scientific use of your test?

Compare the readings of two instruments that calculate their results in different ways.

 

>2. What is its practical use?

Calibrating instruments comes to mind.

 

>3. What is it based on?

Observations of measurements taken over time on a single spot.

 

>4. Where is the RUBBISH?

 

Your posts, primarily. Just a stream of mathmatical psuedo-babble. You name-drop mathmatical terms, but don't seem to have any clue how they are used. Then you cite definitions for no apparent reason with poorly done links.

 

The real kicker was when you made a big deal about your being in the to 10% in mathmatics in the USA. I hate to break your bubble, but I'm in the top half of the top 1% as far as math is concerned. That puts me in a group of about 1.5 million people, many of them professional mathemeticians who could easily kick my butt in this area.

 

So, no. No one was impressed with your 10% play. All it did was make us was put a glaring spotlight on your tenuous grasp on numbers.

 

I'm sorry if the experiment didn't meet your demanding "standards", but this was set up for a 6-th grader's science fair project, not a doctoral thesis. It met Intel's guidelines for how a display of this sort should be set up and presented.

 

Case closed. Bye, Bye.

 

Any further discussion will have to be off-line.

 

George

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Geo your attitude and senseless questions, mumbo gumbo about things you have absolutely no idea about are absolute rubbish. And if you want some links to some of your other senseless rubbish then I will gladly oblige.

 

Here is you lifejacket, anyone else? have some manners, I'll take you task anytime and there's already plenty of links without wasting more time with your pathetic rubbish.

 

Cheers, Kerry.

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