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Sonic_7

Should I have WAAS/EGNOS enabled on my GPS ?

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I'm a newbie to the world of GPS so forgive me if I ask some very basic questions.

 

I have the option to enable/disable WAAS/EGNOS on my new GPS but have no idea what it will give me so can't decide what to do.

 

Any advice/comments appreciated.

Edited by Sonic_7

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SBAS (as the whole system is really called) On is better than having it Off.

It should improve your position fix by 2-4 times.

But I'm not sure if EGNOS is fully On yet.

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It improves your accuracy of the reading. Does it help to find caches?? - probably not but what could it hurt to be more accurate overall??

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I guess it won't harm to turn it on then.

 

Thanks for taking the time to reply to my post.

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I guess it won't harm to turn it on then.

 

Thanks for taking the time to reply to my post.

 

I have not found any advantage in the UK .it also runs the battery down faster as it frantically searches for the elusive waas/egnos birds!

Dave

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I have not found any advantage in the UK .it also runs the battery down faster as it frantically searches for the elusive waas/egnos birds!

perhaps why I said what I said in sentence #3 of my post.

But as for it 'using' up more battery power, that's an urban myth. If you actually have emperical data for that claim please provide it here, everyone here would love to know the truth about that.

Does your TV use up twice as much power when you have PIP (Picture In Picture) running?

Does your GPSr use up lots less power when it's 12 channel receiver is only seeing 3 satellites? If all 12 channles are being used is the miniscule difference in power consumption even detectable? WAAS is just one of those 12 channels, or two sometimes.

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Answer from garmin on the same question;

IF you don't have a Egnos reception in your area, you better turn it it off, because you have a better fix and the location will be more accurate.

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...SBAS (as the whole system is really called)...
Um... no.

 

SBAS is an acronym for "Satellite Based Augmentation Systems." This is a generic term -- it doesn't refer to "the whole system" or any one system specifically. WAAS is one implementation of an SBAS, EGNOS is another, and there are several more.

 

See also: http://en.wikipedia.org/wiki/GNSS_Augmenta...entation_System

 

People who think they know everything are really annoying to those of us who do :)

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...it also runs the battery down faster...
... that's an urban myth. If you actually have emperical data for that claim please provide it here, everyone here would love to know the truth about that.

Actually, some of Garmin's own product manuals specifically state that turning on WAAS can shorten battery life. See page 11 of the Garmin Map 60 manual, for example.

 

Does your TV use up twice as much power when you have PIP (Picture In Picture) running?

Does your GPSr use up lots less power when it's 12 channel receiver is only seeing 3 satellites? If all 12 channles are being used is the miniscule difference in power consumption even detectable? WAAS is just one of those 12 channels, or two sometimes.

Bad analogy. Number of satellites in view doesn't drain more or less battery, it's extra calculations and processor being worked harder. Garmin's power saving modes work mainly by reducing processor load - less frequent sampling, not doing WAAS calculations, etc.

 

That said, impact of WAAS on battery life is significantly less on newer models (due to better processor design) and I would guess WAAS always been less of a factor for battery life than things like backlighting.

 

Now, to really get back to the OP question -- if you're within a few hundred miles of a WAAS ground station...

 

http://maps.google.com/maps?q=http://bbs.k...mp;t=k&om=1

 

... your fixes will generally be better with WAAS enabled.

Edited by lee_rimar

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if you're within a few hundred miles of a WAAS ground station...

 

... your fixes will generally be better with WAAS enabled.

 

Distance from ground stations are not an issue at all. As long as you are within the WAAS coverage area. Once data from the ground stations are sent to the master stations the entire WAAS coverage area is modeled into a correction grid and any reference to the ground station are thenceforth irrelevant.

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Answer from garmin on the same question;

IF you don't have a Egnos reception in your area, you better turn it it off, because you have a better fix and the location will be more accurate.

Is there any way to tell from the GPS unit if it's receiving Egnos/waas signal? Being on the coverage area does not automatically imply that the signal is being received.

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Answer from garmin on the same question;

IF you don't have a Egnos reception in your area, you better turn it it off, because you have a better fix and the location will be more accurate.

Is that a recent answer, or an old one?

 

Early Garmin WAAS implementations were very, very broken such that enabling WAAS could actually decrease your accuracy. It is NOT the fault of the WAAS system; the fault lay entirely with Garmin.

 

But I thought they fixed the problem five or six years ago, so I would be very surprised if they were still giving the same advice.

 

Correct answer: for a correct WAAS implementation, WAAS corrections will only make the fix more accurate, and never less accurate. That is true whether you are in the WAAS coverage area or not.

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And being within a few hundred miles of a station will only impact your IONO corrections, you still can get FAST and LONG corrections, no matter where you are, and those can help improve position accuracy.

I wonder if anyone has a reference of the contributions of those individual 3 kinds of WAAS corrections (vs no corrections) to ones PDOP, HDOP or VDOP?

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Is there any way to tell from the GPS unit if it's receiving Egnos/waas signal? Being on the coverage area does not automatically imply that the signal is being received.

If I were you, I'd use it. The GIVE is currently looking pretty good in Southern Finland.

 

On your unit, go to

Main Menu

Setup

System

WAAS/EGNOS (set to Enabled)

 

Then

Main Menu

Satellite

 

The unit will show the NMEA numbers of the birds it is getting signal for.

EGNOS numbers are:

NMEA #33

NMEA #37

NMEA #39

 

You will get a hollow bar as the data is being downloaded. Wait and get a good set. After it is complete, the bar will turn solid color and you should see the letter D on the signal bars for the birds that are being corrected.

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I notice that my Garmin Legend (2 years old)doesn't hold a fix very good in the woods. I get a message that I need to find open sky, though in my opinion I'm not in really thick woods. If that were the case, why can I fix on satellites in my living room with out any problem? After reading the manual am I to understand that having WAAS enabled and my location might be the problem? I didn't have this problem in the same areas with my bargain basement Lowrance unit.

Edited by pretzelmandan

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I notice that my Garmin Legend (2 years old)doesn't hold a fix very good in the woods.

What version GPS software/firmware is in the unit?

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1. On later model Garmins, the impact of WAAS on battery life is negligible, as my own current consumption tests on a Summit HC show. (No measurable difference in battery current whether WAAS was turned on or off.)

 

2. Older model Garmins had a "Battery Save" mode, which was incompatible with WAAS, because it effectively turned the receiver off intermittently, whereas WAAS requires a continual lock to be effective. This mode does not even exist on some of the new models (e.g. Summit HC - don't know about Oregon, Colorado, etc).

 

3. Older Garmins used to have the problem that having WAAS turned on when outside the WAAS ground station coverage could actually decrease accuracy. This seems to have been fixed on later models, and later software releases: http://forums.Groundspeak.com/GC/index.php...185697&hl=# It seems that when you are outside the ground station coverage area, the newer units will still use the clock and ephemeris corrections (which are valid world-wide), but will ignore the ionosphere corrections (which are only valid locally). However, the ionosphere errors are the biggest of the three, so the benefit of using WAAS when you are outside the ground station coverage area is not all that significant.

 

Bottom line - if you have a late model Garmin, with current software, you might as well leave WAAS on all the time - the downsides are negligible. You probably won't see any great improvement in accuracy, but you almost certainly won't see any degradation in accuracy or battery life either.

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I notice that my Garmin Legend (2 years old)doesn't hold a fix very good in the woods. I get a message that

If you have done a master reset then you would need to re-acquire the whole satellite almanac, minimum of 12.5 minutes in open sky.

From then on, your GPSr should be able to maintain a fix, with snipets of signal from different satellites, some obscurred by trees and so on, while traipsing through the woods. But with a patch antenna, your Legend has half the sky blocked by your body if you hold it right in front of your chest.

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And being within a few hundred miles of a station will only impact your IONO corrections, you still can get FAST and LONG corrections, no matter where you are, and those can help improve position accuracy.
Like EraSeek said, as long as you are inside the iono grid, the distance to the nearest station doesn't really matter. Local affects get washed out in the network.

 

I wonder if anyone has a reference of the contributions of those individual 3 kinds of WAAS corrections (vs no corrections) to ones PDOP, HDOP or VDOP?
It's zero, zero, and zero. Errors are not a part of the DOP calculation.

 

1. On later model Garmins, the impact of WAAS on battery life is negligible, as my own current consumption tests on a Summit HC show. (No measurable difference in battery current whether WAAS was turned on or off.)
I think the difference from older models is that the error correction algorithm went from being done in software to being done on the tracking chip. FEC is a CPU hog.

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I notice that my Garmin Legend (2 years old)doesn't hold a fix very good in the woods.

What version GPS software/firmware is in the unit?

It is version 3.70. Are there updates available?

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I notice that my Garmin Legend (2 years old)doesn't hold a fix very good in the woods.

What version GPS software/firmware is in the unit?

It is version 3.70. Are there updates available?

I think it up to v3.9, you might run the webupdater and see where you stand.

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Hi,

in the last year i have experience, other geocachers also in my area, that when you are there, you are over there, and moved again.

Silly but, we do not have sometimes a steady poi. It is like it is moving.

However, disabling WASS/Egnos we do have a steady poi, and still the 3m accurassy.

 

I am using 60CSX

 

I hear WASS still is not reliable.

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I wonder if anyone has a reference of the contributions of those individual 3 kinds of WAAS corrections (vs no corrections) to ones PDOP, HDOP or VDOP?
It's zero, zero, and zero. Errors are not a part of the DOP calculation.

OK, I really said, I wonder if anyone has a reference of the contributions of those three kinds of SBAS corrections to the precision of ones position FIX.

I.E. With 1 satellite having it's signal corrected with LONG, is the precision still 95% within 10 meter radius?

How about 10 of them being LONG corrected?

How about 1 through 12 of them being FAST corrected? Necessarily having some LONG corrections too.

Or 1-12 of them being IONO corrected? And by necessity you must have LONG and FAST corrections in order to get IONO corrections.

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The unit will show the NMEA numbers of the birds it is getting signal for.

EGNOS numbers are:

NMEA #33

NMEA #37

NMEA #39

 

You will get a hollow bar as the data is being downloaded. Wait and get a good set. After it is complete, the bar will turn solid color and you should see the letter D on the signal bars for the birds that are being corrected.

 

After two days of casual observation, those satellites tend to stay very low on my horizon (I live in Finland). Best what I've seen has been about half way between the horizon and 45 degree circle on the GPSr display. I have to be on very open place to get signal on those and wait for several minutes for a lock.

Do these satellites have different technology as "recycling" the GPS unit to reset possible accumulated drift will not result to instant lock, but again the long wait? Other satellites are instant lock when recycling.

 

Is there a site where one could see the flight paths/schedules of those satellites? I could alter my mapping expeditions if there is good satellite reception to be expected by waiting one or two hours..

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Is there a site where one could see the flight paths/schedules of those satellites? I could alter my mapping expeditions if there is good satellite reception to be expected by waiting one or two hours..

Those birds are geosynchronous/geostationary, they do not move, much.

Picking them up should be similar to a warm start.

Actually having their signals used to correct the signals from the GPS semi-synchronous birds might take a while for the full correction transmission to be acquired, and for the corrections to get calculated. But once they are being used, they should continue to work, somewhat, when you move about and lose lock on those signals temporarily.

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After two days of casual observation, those satellites tend to stay very low on my horizon (I live in Finland). Best what I've seen has been about half way between the horizon and 45 degree circle on the GPSr display. I have to be on very open place to get signal on those and wait for several minutes for a lock.

Do these satellites have different technology as "recycling" the GPS unit to reset possible accumulated drift will not result to instant lock, but again the long wait? Other satellites are instant lock when recycling.

The purpose of any SBAS system is to provide data that will allow your GPS to correct the GPS satellite triangulations for things like ionospheric distortion and other factors that will affect its accuracy. In order to do this, your GPS receiver must find a satellite (WAAS or EGNOS) that is broadcasting the necessary correction data. Then it must collect all of the data into an "almanac" (fancy word for a database) before it can use it. There is a lot of data and the transmission speed is quite slow.

 

When you do the reset ("recycling" as you called it), you empty the almanac and so it must be completely collected again the next time the receiver finds a satellite transmitting the data. On Garmin GPS receivers, the signal strength bar on the WAAS/EGNOS satellite will stay outlined rather than solid until the complete almanac has been captured again. As someone else mentioned a few messages back, that takes 12 minutes or more. How long it takes depends upon where in the transmission stream the GPS receiver starts collecting the data and how good the reception is. If the receiver encounters data errors when receiving, it can't simply ask for a retransmission of the errored data. It must wait until the transmission cycles all the way back to that data in the next iteration.

 

In simple terms, even in perfect conditions it will take far more time to capture the correction data from the WAAS/EGNOS transmission than it will to get a lock on the other satellites.

 

It has also been mentioned in here, and in many other discussion threads on the subject, that the value of WAAS/EGNOS corrections in consumer-grade GPS receivers is minimal for most practical uses. I have an eTrex Legend HCx. With a full 3D Differential lock on 10 satellites (all visible satellites locked and corrected) I generally get an accuracy report of 2 metres in the best conditions. With WAAS disable in those same conditions I get an accuracy report of 3 metres. (The accuracy report is another discussion because most people misunderstand what it really means.)

 

It's fun to play with this stuff and see how it works, and it's interesting to learn more about it. But in normal use it provides little practical value for most of us, in my experience.

 

...ken...

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Both my old blue Etrex, and the GPSMAP60CX indicate which WAAS satellites they are receiving. In my case, in my area, the two satellites are sketchy to nil most times. This tends to make the units lock up on mapping, updates, and compass. I have discovered that turning off the WAAS capability increases speed of acquisition, accuracy .

 

I leave it off, and have better accuracy and battery life that way, but I am in an area where the signals are unreliable.

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I notice that my Garmin Legend (2 years old)doesn't hold a fix very good in the woods.

What version GPS software/firmware is in the unit?

It is version 3.70. Are there updates available?

I think it up to v3.9, you might run the webupdater and see where you stand.

Thanks, I was able to update to 3.9 and then set it out side for a half hour to recharge the almanac. I notice some improvement but it isn't quite what I had hoped.

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Is there a site where one could see the flight paths/schedules of those satellites? I could alter my mapping expeditions if there is good satellite reception to be expected by waiting one or two hours..

There is actually a software package that allows you to estimate DOP based on satellite positions.

You can plan for times with good satellite placement using that program.

http://www.trimble.com/planningsoftware.shtml

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....

You will get a hollow bar as the data is being downloaded. Wait and get a good set. After it is complete, the bar will turn solid color and you should see the letter D on the signal bars for the birds that are being corrected.

 

Are you sure about the hollow bar significance? I thought the unit displayed hollow bars for units that it had almanac data for (rough information about all satellites available from any satellite) whilst it was downloading enough ephemeris data (specific to that satellite and available only from that satellite) to get a more accurate fix on its orbit - after that the bar turns solid. Then, if the unit can see the EGNOS satellites the unit applies correction data received from them and D appears on all satellites that it is receiving EGNOS data for - this information having been calculated from information received through the ground network grid and sent up to the 3 EGNOS satellites.

 

So, strictly you only need to receive data from one of those satellites to provide corrected data for all GPS or GLONASS satellites in that area.

 

This is as far as I can determine anyway.

 

-Andy

Edited by iamasmith

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....

You will get a hollow bar as the data is being downloaded. Wait and get a good set. After it is complete, the bar will turn solid color and you should see the letter D on the signal bars for the birds that are being corrected.

 

Are you sure about the hollow bar significance? I thought the unit displayed hollow bars for units that it had almanac data for (rough information about all satellites available from any satellite) whilst it was downloading enough ephemeris data (specific to that satellite and available only from that satellite) to get a more accurate fix on its orbit - after that the bar turns solid. Then, if the unit can see the EGNOS satellites the unit applies correction data received from them and D appears on all satellites that it is receiving EGNOS data for - this information having been calculated from information received through the ground network grid and sent up to the 3 EGNOS satellites.

 

So, strictly you only need to receive data from one of those satellites to provide corrected data for all GPS or GLONASS satellites in that area.

 

This is as far as I can determine anyway.

 

-Andy

What you've described is true for the normal GPS satellites. What coggins was referring to is the bar for the WAAS/EGNOS satellite. That bar will be hollow while it's downloading correction data for the normal GPS satellites. Once it's completed its initial download, the bar will turn solid and you will see "D" on the bars for the normal GPS satellites for which it has correction data.

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I'm a newbie to the world of GPS so forgive me if I ask some very basic questions.

 

I have the option to enable/disable WAAS/EGNOS on my new GPS but have no idea what it will give me so can't decide what to do.

 

Any advice/comments appreciated.

 

in my case i keep it off - when it is on i get 30 feet of error - with it off i get 3 to 6 feet of error :wub:

 

errors could be from a faulty precessor who knows :D

 

etrex legend :D

 

when i go caching without waas i find caches like crazy - when waas is on when caching i get huge number of no finds :D

Edited by KD7MXI

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The unit will show the NMEA numbers of the birds it is getting signal for.

EGNOS numbers are:

NMEA #33

NMEA #37

NMEA #39

 

You will get a hollow bar as the data is being downloaded. Wait and get a good set. After it is complete, the bar will turn solid color and you should see the letter D on the signal bars for the birds that are being corrected.

 

After two days of casual observation, those satellites tend to stay very low on my horizon (I live in Finland). Best what I've seen has been about half way between the horizon and 45 degree circle on the GPSr display. I have to be on very open place to get signal on those and wait for several minutes for a lock.

Do these satellites have different technology as "recycling" the GPS unit to reset possible accumulated drift will not result to instant lock, but again the long wait? Other satellites are instant lock when recycling.

 

Is there a site where one could see the flight paths/schedules of those satellites? I could alter my mapping expeditions if there is good satellite reception to be expected by waiting one or two hours..

 

Couldn't find a site to track EGNOS satelittes but this link will take you to FAA web site to track WAAS

satelittes. On the left side click on WAAS Satellite Status.

 

Hope this is useful.

 

http://www.nstb.tc.faa.gov/index.htm

Edited by Fixman1

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Couldn't find a site to track EGNOS satelittes but this link will take you to FAA web site to track WAAS

satelittes. On the left side click on WAAS Satellite Status.

My post in http://forums.Groundspeak.com/GC/index.php...t&p=3711393 has the exact orbital elements of the EGNOS and WAAS and MSAS satellites that are just aobut as current as you can get.

 

Plug those into any satellite tracking program, or the Trimble GPS planning software that I mention in this thread and you will see exactly where those stationary satellites are all the time.

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