Got A Question About Waas

[+russell_53040]

I just got my gpsr yesterday and it says something about WAAS. Do you recomend using WAAS or Not using it? Oh I got the Garmin eTrex Legend.

[+briansnat]

I've found little difference with it on or off, so I have it off. Your experiences may differ, so try it each way and decided for yourself.

[+russell_53040]

What is it suppose to do?

[+globalgirl]

Well I dunno about Garmin, but on my Magellan Sportrak Map, WAAS is automatically enabled, with no means of turning it off (nor can I imagine why you'd want to.)

 

And yes, yes, in my expereince WAAS greatly increases the accuracy of the unit - often cutting my EPE (error rate) in half.

 

And while I don't presume to know precisely how it works, suffice that my user guide states it thusly:

 

"WAAS is a means of improving the accuracy of GPS beyond the standard civilian signal. WAAS was developed by the FAA to provide the accuracy needed for aircraft to perform approaches for landings. WAAS improves the accuracy of GPS by calculating the errors in the GPS signal at several monitoring stations around the country and then transmitting the error corrections to special WAAS satellites. In turn, these satellites broadcast the error corrections to WAAS-capable GPS receivers around the world."

 

I also understand that these corrections are of errors in atmospheric conditions, etc. (and thus the land based statiions down here in the soup vs. satts above the atmosphere), and it seems those special WAAS birds aren't always available. But when they are - I've seen my accuracy on a micro jump from 60 ft. away from the actual hide to RIGHT ON TOP of the bison tube - simply via the WAAS satts kicking in.

[+Marietta Moose]

Try this link for a good explanation of Waas:

 

WAAS Explanation

 

I have found my GPS is much more accurate with it on if the GPS can see Sat #35 which is the WAAS satellite in my area (Georgia).

 

You gotta love technology.

 

MM

[+StarBrand]

Not always but as a general rule WAAS improves the accuracy and reduces the jumping sometimes seen as you near a cache. I am able to get the WAAS corrections about 75% of the time - need a clear view to the Southeast Horizon -generally (from here anyway). On your legend - watch for the little D on your sat page indicating that you are receiving corrections. There are a lot of varibles with WAAS including your distance to the nearest ground station, atmospherics, etc. But when you can get sat 35 - it works great!!

[Stony2008]

I have a etrex legend also. I just leave mine on I dont notice a difference either but it doesnt hurt to leave it on.

[+StarBrand]

I have a etrex legend also. I just leave mine on I dont notice a difference either but it doesnt hurt to leave it on.

You do lose 10 - 20% of battery life with it on.

[+Marcie/Eric]

Why would you even turn it off? Bettery consumption is the only possible reason, and theoretically, WAAS should be just like recieving another sat signal, right? Wouldn't it be the same as the difference between you locking onto 4 sats, and 5 or 6 sats?

 

Not that I know what i'm talking about.

 

-E

Edited March 22, 2005 by Marcie/Eric

[+Cardinal Red]

I can clearly see the difference in estimated "Accuracy" with WAAS on (Garmin MAP 76S) .

[+JohnnyVegas]

A better WAAS link

 

WAAS

[+VirginiaJim]

Under certrain conditions-say, when weak WAAS satellite signals are being received or the GPS receiver is a long way from a ground station-accuracy can actually worsen when WASS is enabled.

 

I found this information in Geocaching for Dummies by Joel McNamara

[+robert]

I just leave it off. Doesn't give me any benefit that I've found.

 

edit: gps is a 60CS

Edited March 24, 2005 by robert

[+mantis7]

Granted Ive only had my WAAS enabled GPSr for a few hours...(Just long enough to do the updates, download my maps & waypoints, and find two caches before dinner) BUT...

 

My GPSr came with WAAS disabled as a default, and as soon as I turned it on I noticed an increase in the accuracy and the "jumpiness" of the distance from cache....

 

Like I said this is only after a few hours of playing with it, but it seemed to make a difference to me.

 

Edit: 76 CS

Edited March 24, 2005 by mantis7

[+robert]

was your increase in accuracy noticed while out in the open? it may not be the same situation when in the woods. go to the satellite screen and look at the bars. how many do you see with a "D" in them? if you want to test out the WAAS reception where you go, look for those "D"s on the sat bars.

[reidster]

Under certrain conditions-say, when weak WAAS satellite signals are being received or the GPS receiver is a long way from a ground station-accuracy can actually worsen when WASS is enabled.

 

I found this information in Geocaching for Dummies by Joel McNamara

In my humble opinion, the author's statement is boooooooooooooogus!

 

WAAS signals, like all other GPS signals, are highly sophisticated digitally encoded messages. Included in the WAAS message stream is the Iono-Grid correction information.

 

The two Master Stations, with data collected from the 25 ground reference stations, generate ionospheric corrections for points on a grid covering most of North America. This information is then sent up to the WAAS satellites, which are re-broadcast to your GPSr. A WAAS enabled GPS receiver receives this data and interpolates the appropriate correction based on its location in relation to the nearest three or four grid points. Corrections are accurate within the grid area regardless of how far it is from a ground reference station.

 

Therefore if a GPSr indicates WAAS reception, accuracy should only improve. If it doesn't, I would have serious doubts about the unit's firmware and reliability. If I'm wrong about this, I'll happily accept any correction to the contrary and appreciate the education.

[+WalruZ]

If I'm hunting for a cache and I can't find the darn thing, I'll turn WAAS off if it's on, and on if it's off. It makes me feel better...

[+gnbrotz]

At first, I had spotty results with WAAS (etrex Legend), then I read somewhere that in order to work at it's peak, it needs to build almanac data, similar to what you'd do after a hard reset or long distance travel with your unit off. I found a place where I could get a good WAAS signal and left the unit for 20-30 minutes. Ever since I've done that, I routinely get an excellent corrected signal quickly, and have seen a significant decrease in my reported EPE.

[+Thot]

My experience is with a Magellan 315 which I started geocaching with, and my current SporTrack Pro. The 315 is not WAAS capable, the SporTrack is. In Houston and surrounds I have found the SporTrack gets me much nearer the cache than the 311 did. I also tested both models against high accuracy USGS benchmarks. The SporTrack would typically get me 8-15 feet from the benchmark, whereas the 311 was more like 25-40 feet. Of course, since the error is random within a certain size circle, both units would sometimes get me right on top of a cache, but that’s simply random chance.

 

I really think the only way to assess this is to use the same unit and make multiple trys at different times of the day and on different days using WAAS for half of the trials, but not every other trial. Whether the trial is WAAS or not should be randomly selected. Here is a pattern of 24 trials that should work:

 

WAAS WAAS WAAS WAAS WAAS not WAAS not not not WAAS not WAAS WAAS WAAS not not WAAS not not not WAAS not not

 

Or, here’s a set of 12 if you’re unwilling to do 24:

 

not not WAAS not not WAAS not not WAAS WAAS WAAS WAAS

 

Twelve trials won't get the answer unless the pattern is very obvious, such as every trial of one kind is larger than every trial of the other kind. But, it should be suggestive.

 

Edited typos

Edited March 25, 2005 by Thot

[Stony2008]

I have a etrex legend also. I just leave mine on I dont notice a difference either but it doesnt hurt to leave it on.

 

You do lose 10 - 20% of battery life with it on.

 

I forgot to tell you I have rechargeable. another good investment in owning a gps .

[+Team Cotati]

Under certrain conditions-say, when weak WAAS satellite signals are being received or the GPS receiver is a long way from a ground station-accuracy can actually worsen when WASS is enabled.

 

I found this information in Geocaching for Dummies by Joel McNamara

In my humble opinion, the author's statement is boooooooooooooogus!

 

WAAS signals, like all other GPS signals, are highly sophisticated digitally encoded messages. Included in the WAAS message stream is the Iono-Grid correction information.

 

The two Master Stations, with data collected from the 25 ground reference stations, generate ionospheric corrections for points on a grid covering most of North America. This information is then sent up to the WAAS satellites, which are re-broadcast to your GPSr. A WAAS enabled GPS receiver receives this data and interpolates the appropriate correction based on its location in relation to the nearest three or four grid points. Corrections are accurate within the grid area regardless of how far it is from a ground reference station.

 

Therefore if a GPSr indicates WAAS reception, accuracy should only improve. If it doesn't, I would have serious doubts about the unit's firmware and reliability. If I'm wrong about this, I'll happily accept any correction to the contrary and appreciate the education.

You're right on dude!! Thanks for the contribution.

[+VirginiaJim]

In my humble opinion, the author's statement is boooooooooooooogus!

 

 

.

You will find in multiple discussions about WAAS that poor reception can in some cases reduce the accuracy of your GPS.

 

  We have observed that MOST OF THE TIME WAAS appears to improve averaged accuracy at a fixed location for maybe 5 minutes averaging from about 7 meters to perhaps 3 meters.  Sometimes there has been no improvement and a few times (when WAAS signals were not of good quality or when we were far from a WAAS correction station) the measurements have actually had more error with WAAS than without.

 

WAAS is a tool for casual GPS users.  It is not guaranteed to work,  it is not guaranteed to increase accuracy,  it is not really able to tell you when it will improve accuracy,  when it will have no effect,  or when it will make for less accuracy than the normal GPS signal. Under good conditions when YOU ARE OUT IN THE CLEAR AND RECEIVING A GOOD SIGNAL FROM THE WAAS SATELLITE,  you should get both improved accuracy and improved position stability.  YOU must insure that you have the proper conditions so as to experience the improvement at YOUR location.

 

Joe Mehaffey gspinformation.net

 

In many cache locations you are obviously not out in the open. You are often in mountainous terrain and shielded by trees. Both of these situations interfere with all satellite singals, including WAAS. It appears that there are many sources of GPS information that are "boooooooooooooogus!" in your opinion.

[+tands]

A local hider uses an E-Trex yellow. His caches are great and lots of fun. Since I know his unit doesn't have WAAS I turn it off on his hides and that helps a lot. But on all others the WAAS seems to help. My $.02.

 

- T of TandS

[+Team Cotati]

WAAS gives more accurate coordinate tracking period. If you are not interested in that, don't use it.

 

"You've heard the term WAAS, seen it on packaging and ads for Garmin® products, and maybe even know it stands for Wide Area Augmentation System. Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS."

 

Perhaps the folk over at Garmin are lying. Personally, I think that that is highly unlikely. Nor do I think that they are ignorant gubmint shills.

 

Carry on dudes!!

[+Team Cotati]

WAAS gives more accurate coordinate tracking period. If you are not interested in that, don't use it.

 

"You've heard the term WAAS, seen it on packaging and ads for Garmin® products, and maybe even know it stands for Wide Area Augmentation System. Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS."

 

Perhaps the folk over at Garmin are lying. Personally, I think that that is highly unlikely. Nor do I think that they are ignorant gubmint shills.

 

Carry on dudes!!

 

P.S. I recommend using it at all times.

Edited March 26, 2005 by Team cotati697

[+EraSeek]

In my humble opinion, the author's statement is boooooooooooooogus!

 

 

.

You will find in multiple discussions about WAAS that poor reception can in some cases reduce the accuracy of your GPS.

 

  We have observed that MOST OF THE TIME WAAS appears to improve averaged accuracy at a fixed location for maybe 5 minutes averaging from about 7 meters to perhaps 3 meters.  Sometimes there has been no improvement and a few times (when WAAS signals were not of good quality or when we were far from a WAAS correction station) the measurements have actually had more error with WAAS than without.

 

WAAS is a tool for casual GPS users.  It is not guaranteed to work,  it is not guaranteed to increase accuracy,  it is not really able to tell you when it will improve accuracy,  when it will have no effect,  or when it will make for less accuracy than the normal GPS signal. Under good conditions when YOU ARE OUT IN THE CLEAR AND RECEIVING A GOOD SIGNAL FROM THE WAAS SATELLITE,  you should get both improved accuracy and improved position stability.  YOU must insure that you have the proper conditions so as to experience the improvement at YOUR location.

 

Joe Mehaffey gspinformation.net

 

In many cache locations you are obviously not out in the open. You are often in mountainous terrain and shielded by trees. Both of these situations interfere with all satellite singals, including WAAS. It appears that there are many sources of GPS information that are "boooooooooooooogus!" in your opinion.

You are using a very old link:

 

GPS WAAS Operation: Your questions Answered.

by Joe Mehaffey

(revised: 28 July 2002)

 

Reidster is correct. Joe Mehaffey has fresher links. If you look at all of Joes info you will find a lot of contradictions. Fact is WAAS has improved since then and so has the GPS hardware and firmware. Fact is the distance from ground station make VERY little difference as to accuracy. THAT IS the beauty of WAAS over regular DGPS. WAAS is a model grid and your GPS is an essential active part of the system. Try the link next to the one you found. It has better info.

[+Team Cotati]

In my humble opinion, the author's statement is boooooooooooooogus!

 

 

.

You will find in multiple discussions about WAAS that poor reception can in some cases reduce the accuracy of your GPS.

 

  We have observed that MOST OF THE TIME WAAS appears to improve averaged accuracy at a fixed location for maybe 5 minutes averaging from about 7 meters to perhaps 3 meters.  Sometimes there has been no improvement and a few times (when WAAS signals were not of good quality or when we were far from a WAAS correction station) the measurements have actually had more error with WAAS than without.

 

WAAS is a tool for casual GPS users.  It is not guaranteed to work,  it is not guaranteed to increase accuracy,  it is not really able to tell you when it will improve accuracy,  when it will have no effect,  or when it will make for less accuracy than the normal GPS signal. Under good conditions when YOU ARE OUT IN THE CLEAR AND RECEIVING A GOOD SIGNAL FROM THE WAAS SATELLITE,  you should get both improved accuracy and improved position stability.  YOU must insure that you have the proper conditions so as to experience the improvement at YOUR location.

 

Joe Mehaffey gspinformation.net

 

In many cache locations you are obviously not out in the open. You are often in mountainous terrain and shielded by trees. Both of these situations interfere with all satellite singals, including WAAS. It appears that there are many sources of GPS information that are "boooooooooooooogus!" in your opinion.

You are using a very old link:

 

GPS WAAS Operation: Your questions Answered.

by Joe Mehaffey

(revised: 28 July 2002)

 

Reidster is correct. Joe Mehaffey has fresher links. If you look at all of Joes info you will find a lot of contradictions. Fact is WAAS has improved since then and so has the GPS hardware and firmware. Fact is the distance from ground station make VERY little difference as to accuracy. THAT IS the beauty of WAAS over regular DGPS. WAAS is a model grid and your GPS is an essential active part of the system. Try the link next to the one you found. It has better info.

What happens to the system if you turn your GPSr off?

[+EraSeek]

Then you can not take advatage of it.

 

Your GPS is part of the WAAS system because it has downloaded the almanac. Thus the system relies on your GPS to determine its position in the modeled grid so it can apply the proper correction for that particular spot in the grid.

 

If you turn your GPS (or WAAS) off you don't get to take part in the system. Only your lose, not the systems.

[+JohnnyVegas]

Not usng WAAS makes about as much sense as trying to build a house without a tape measure, sure you can do,it, but not very well. WAAS is a tool used for navigation, it makes no sense to not use it.

 

Maybe Joe Mehaffey should move all the old out dated information into a new area of his web site and call it Usless out dated data

[+VirginiaJim]

Not usng WAAS makes about as much sense as trying to build a house without a tape measure, sure you can do,it,  but not very well. WAAS is a  tool used for navigation, it makes no sense to not use it.

 

WASS is a wonderful tool. I use it often. I'm not saying don't use WAAS. Of course, it improves the accuracy of your GPS in many cases. However, like any tool, including tape measures, it has its limitations and there are multiple sources of imformation (old and new) that confirm that. If you do not take into account the limitations you can not use any tool effectively.

 

How has WASS improved over the last few years? Are there more ground stations? Are there still not only two WAAS satellites that cover the US? Is the signal of a better quality? What about funding for GPS and WAAS satellites during the Bush administration?

 

It is great to have a place to discuss things associated with geocaching. I appreciate those who sincerely wish to share there input in a positive manner. Because of this forum topic, I'm researching and learning much more about WAAS.

 

A thought as I head out with my WAAS enabled GPS to go geocaching for the afternoon. I feel that everyone should consider being a premium member and help support the site that we all enjoy.

[+Kai Team]

I have an eTrex Vista and always use WAAS. I use rechargable NiMH batteries and always carry two spare pairs so I'm not worried about the drain on the batteries, which is the ONLY downside to using WAAS (and the only reason Garmin provides a means to turn it off!).

 

Considering that WAAS was developed to aid aircraft landings, it's illogical to believe that it degrades accuracy (if there are any IFR pilots reading this - do you ever turn WAAS off when approaching an airport in thick fog?).

 

There are far too many variables for the average cacher to conduct a valid test of WAAS: logically, WAAS either improves accuracy or it has no effect (when the WAAS signal is intermittent or unavailable due to terrain). Of course, people have a right to believe whatever they want to believe - that's what makes this Country great!

[+VirginiaJim]

Perhaps the folk over at Garmin are lying. Personally, I think that that is highly unlikely. Nor do I think that they are ignorant gubmint shills.

 

Carry on dudes!!

For the most part, I agree with your assessment of Garmin. I do not think they are shills. I do not think they are lying. However, corporate America has often proved itself untrustworthy.

 

In addition, I think they understand that their units do have limitations. If you read the "Warnings and Cautions" in their manuals for the hand held units you see this in CAPITAL letters,

 

THIS PRODUCT IS INTENDED TO BE USED ONLY AS A TRAVEL AID AND MUST NOT BE USED FOR ANY PURPOSE REQUIRING PRECISE MEASUREMENT OF DIRECTION, DISTANCE, LOCATION, OR TOPOGRPHY.

 

It appears Garmin realizes there are limitations to the technology as well. It appears that their lawyers want to make it clear that their handhelds have limitations to avoid lawsuits.

 

As I said, off to go geocaching. One more question as I go, does any one have any "FACTS" from reliable up to date sources that claim their are no limitations to WAAS?

[+EraSeek]

Not usng WAAS makes about as much sense as trying to build a house without a tape measure, sure you can do,it,  but not very well. WAAS is a  tool used for navigation, it makes no sense to not use it.

 

WASS is a wonderful tool. I use it often. I'm not saying don't use WAAS. Of course, it improves the accuracy of your GPS in many cases. However, like any tool, including tape measures, it has its limitations and there are multiple sources of imformation (old and new) that confirm that. If you do not take into account the limitations you can not use any tool effectively.

 

How has WASS improved over the last few years? Are there more ground stations? Are there still not only two WAAS satellites that cover the US? Is the signal of a better quality? What about funding for GPS and WAAS satellites during the Bush administration?

 

It is great to have a place to discuss things associated with geocaching. I appreciate those who sincerely wish to share there input in a positive manner. Because of this forum topic, I'm researching and learning much more about WAAS.

 

A thought as I head out with my WAAS enabled GPS to go geocaching for the afternoon. I feel that everyone should consider being a premium member and help support the site that we all enjoy.

Of coarse anything has limitations. Everything does.

(I am doing this from memory without refering back to various sites...) WAAS was orginally in "Test" phase for quite awhile, yet still availible to the public to use. It is now instituted as "usable" (or whatever their term is) for everyday reliable use. Yes, there are still only 2 WAAS sats that relay information for the coverage area (the US and a bit more) and if one of these sats fails some of the US will not have WAAS coverage. They do have more sats planned which will provide better access to the signal in more places (say if your sat is blocked by a canyon wall) and as backup to the other 2. There may also be a boost of power on the signal to improve reception. There is also a duel-band civilian system in the works. The point is, right now, if you are in line of sight of a WAAS sat in or near the US you will have improved accuracy IF there are corrections needed. Sometime the ionosphere causes havoc with you sat signals, slows them down and throws your coods off. WAAS DOES improve this with corrections. Sometimes corrections will not be much, sometimes they will. WAAS also corrects other errors as well, but the ionosphere is the biggest correction.

There have also been improvments in hardware and firmware. Used to be the unit would try and use a WAAS sat for a fix no matter what. WAAS sat relay the almanac but they can also be use fro a postion fix. Now they are only used if it makes sense for improved postion fixes. This is why in the past a WAAS sat could make your postion worse.

Joe has some great info and also a ton of links. Some time you just need to look at the date o the info and question the older stuff.

[+VirginiaJim]

Considering that WAAS was developed to aid aircraft landings, it's illogical to believe that it degrades accuracy (if there are any IFR pilots reading this - do you ever turn WAAS off when approaching an airport in thick fog?).

 

A point well made. I know of now pilots that turn it off as they approach a landing. It is a system that was designed to be used for this. A system that works well in areas of open terrian such as airports. I also know of no pilots that rely exclusively on the technology as they land. In fact, I was amazed at its accuracy when I took a couple of introductory flying lessons. Some day I would like to take up flying as a hobby, but my wife does have her limits with my hobbies and the price of fuel! She might understand another GPS unit, but she might get upset over a plane.

 

Your conclusion that it is illogcial that the system could not degrade performance in other conditions is where I have to disagree.

 

Navigation tools all the way back to the discovery of the compass have had their limitations. Navigators have always used mutliple tools to verify their locations. I think WAAS is great! I use it often, but it is only a technology that has its limitations.

 

While in the Navy I was aboard several submarines, including the USS Francis Scott Key SSBN 657. We used multiple navigation systems for navigation and weapons control. Radar, sonar, gyros, compasses, even the periscope while entering the Mediterranean Sea. Everyone new the limitations associated with each of the technologies. It would have been dangerous and illogical to believe that one technology didn't have limitations or degraded performance in certain situations.

 

Yes America is great! However, it has its imperfections, as does WAAS.

 

I better get going geocaching before the day is over.

[+JohnnyVegas]

In addition, I think they understand that their units do have limitations. If you read the "Warnings and Cautions" in their manuals for the hand held units you see this in CAPITAL letters,

 

It appears Garmin realizes there are limitations to the technology as well. It appears that their lawyers want to make it clear that their handhelds have limitations to avoid lawsuits.

 

It appears that their lawyers want to make it clear that their handhelds have limitations to avoid lawsuits.

 

You can bet all the warnings are place at the request of the Legal dept at Garmin, Not because of any problems in the GPSr or system, they are more than likely there because of the person that thinks they can check a property line with a consumer grade GPS and end gettng sued , or the person that just follows a navigation arrow as the crow flies and winds up gettie hurt when they take a fall , or how about those we read about the get lost with there GPS because they have not read the directions and do not know how to run a back track with a GPS or how to set a route as they enter a area they are not familiar with.

 

There are lots of people that are going to sue a company because of there own stupidity, and there are lots of attournies that will file a suit if they think there is even a small chance of collecting. Even if a company wins a suit they still have to pay a ton of money to defend themselves.

 

Or how about new caches that have bad coordinates that are in the medium strip of a highway, or the cacher that enter bad coordinates, who do you think there family would look to sue if they were run over trying to cross a highway to get to a spot were they think there is a cache.

 

Just read any cache page an you will see a warning posted to protect grounspeak from idiots that get into trouble while geocaching. I don't what it is like outside the USA but we are a society full of people that want to sue someone else for their own stupidity. i am sure a large part of the problem has to do with the over population of attournies

 

Edit to add: from groudspeak Disclaimer link

Geocaching Disclaimer

Geocaching.com is owned and operated by Groundspeak Inc. Information in the Geocaching.com database is updated regularly. Neither Groundspeak Inc., nor any agent, officer, employee or volunteer administrator of Groundspeak Inc. warrants the accuracy, reliability, or timeliness of any information and shall not be liable for any losses caused by such reliance on the accuracy, reliability, or timeliness of such information. While every effort is made to ensure the accuracy of this information, portions may be incorrect or not current. Any person or entity that relies on information obtained from Geocaching.com does so at his or her own risk.

 

Geocaching, hiking, backpacking and other outdoor activities involve risk to both persons and property. There are many variables including, but not limited to, weather, fitness level, terrain features and outdoor experience, that must be considered prior to seeking or placing a Cache. Be prepared for your journey and be sure to check the current weather and conditions before heading outdoors. Always exercise common sense and caution.

 

In no way shall Groundspeak Inc. nor any agent, officer, employee or volunteer administrator of Groundspeak Inc., be liable for any direct, indirect, punitive, or consequential damages arising out of, or in any way connected with the use of this website or use of the information contained within.

Edited March 26, 2005 by JohnnyVegas

[+EraSeek]

Here is a look a what the daily ionosphere would look like. Also it would be simular to what the modeled correction grid would look like. Notice how it is worse mid - day and less so at night

 

http://gpsinformation.net/exe/iono-day.gif

[+EraSeek]

A good discussion on errors.

http://www.edu-observatory.org/gps/gps_accuracy.html

Note the sandard corrections w/o SA goes from 10. something to 3 meters with DGPS(WAAS)

Edited March 26, 2005 by EraSeek

[+EraSeek]

More links: http://www.gpsy.com/gpsinfo/index.html

[+EraSeek]

Realtime WAAS coverage area: http://www.nstb.tc.faa.gov/vpl.html

[+philthebottle]

What is it suppose to do?

To get back to what WAAS is and how it works, here's the easiest to understand link that I've found:

 

http://www.trimble.com/gps/index.html

 

It's even got pictures for those of us who don't care for all that "reading the directions" garbage!

[Grumpy Grampy]

I just bought the bare-bones basic Etrex Personal Navigator which does not even have WAAS as a feature. In a dual cache hunt with my son using his Magellan Meridian with WAAS, my Etrex matched it in directional/distance accuracy, although it was a bit slower picking up on those changes. However, in our final plots to find a cache, the two units were identical. ....FWIW

[+EraSeek]

I just bought the bare-bones basic Etrex Personal Navigator which does not even have WAAS as a feature. In a dual cache hunt with my son using his Magellan Meridian with WAAS, my Etrex matched it in directional/distance accuracy, although it was a bit slower picking up on those changes. However, in our final plots to find a cache, the two units were identical. ....FWIW

The yellow Etrex is a fine unit. No bells and whistles but does the job. Unless you are caching during a red bar (maybe yellow bar) period I would expect your coordinates to be close togther:

http://solar.sec.noaa.gov/rt_plots/kp_3d.html

[+Kai Team]

One more question as I go, does any one have any "FACTS" from reliable up to date sources that claim their are no limitations to WAAS?

Your conclusion that it is illogcial that the system could not degrade performance in other conditions is where I have to disagree.

 

Navigation tools all the way back to the discovery of the compass have had their limitations.  Navigators have always used mutliple tools to verify their locations.  I think WAAS is great!  I use it often, but it is only a technology that has its limitations.

 

Yes America is great!  However, it has its imperfections, as does WAAS. 

Whoa Nelly - I never said WAAS with perfect or "without limitations" - in fact, I pointed out the main one - intermittent or non-existent reception of the WAAS signal. I also never said that you should rely on a single tool to navigate (I still carry a magnetic compass), or that pilots or submariners rely soley on WAAS.

 

However, it is illogical to assume that WAAS will degrade your accuracy - you either receive it and it ehances accuracy, or you don't receive it and it has no effect. I'm assuming, of course, that your GPSr uses WAAS intelligently - it's possible that the major GPS manufacturers install bonehead firmware that causes WAAS to degrade accuracy, but it hasn't been my experience with the eTrex Vista!

[+EraSeek]

It is my understanding that most or all of the problems with how and when WAAS is applied by manufacturer's units (Garmin) has been fixed. Who knows about third rate units? It was not the fault of WAAS but a matter of prioritizing WAAS sats, and putting the units resources an empty hole before it is usable.

 

The limitation include: Inability to get a signal from the WAAS sat as they are somewhat low in the sky or you are in the woods; Need to have WAAS initially enabled (user's fault, they must know to do this); Length of time to download and apply the WAAS almanac before it is usable (what is it? 5 to 12 minutes before the full almanac is downloaded, this is why you will see the EPE or Accuracy reading jump up before dropping back down again).

 

By the way, EPE or Accuracy Readings are ONLY a programed guesstimate. Not Gospel.

[+VirginiaJim]

Back from a wet soggy afternoon of geocaching in central Virginia. Yes, I had WAAS on the whole time!

 

I was able to do a micro, regular, virtual and part of a multi. Monticello, Thomas Jefferson's home, is a great place to visit if you are ever near Charlottesville VA. At present, it has several caches in and around it.

 

If you are ever visiting the area, let me know. I'll buy you lunch, go on a geocaching tour of your choice, and discuss interesting topics like WAAS accuracy. The area code is 22968 if you want to do a search for the area.

 

I wonder if there are any companies that do geocaching vacations? Another topic to explore.

 

Thank you Eraseek and philthebottle for the links. I look forward to checking them out. I appreciate your constructive input and the time you spent looking the links up.

Edited March 26, 2005 by VirginiaJim

[+NightPilot]

Yes, I'm an IFR pilot, and I do it for a living. The GPS units in our aircraft aren't WAAS capable, so no, I don't turn it off because it has never been turned on. I wouldn't turn it off if it were being used, because an aircraft in flight can always receive it.

 

The FAA developed WAAS for a specific reason - vertical accuracy is much less than horizontal accuracy, and they wanted to be able to use GPS for precision instrument approaches, which by definition require vertical guidance. GPS without WAAS has an altitude accuracy that is far too low for this, so WAAS was devised, specifically to improve altitude information to 50' or less so that aircraft equipped with WAAS-capable certified GPS receivers could fly approaches down to 250' above the runway, which is still 50' higher than a standard instrument landing system allows. Any improvement in horizontal accuracy is purely a byproduct, and is minimal, because the standard GPS is more than precise enough for approaches in the horizontal plane, more accurate than even an ILS localizer. The FAA has no interest in geocachers being able to use WAAS, so reception on the ground is not a priority at all. WAAS was never intended to aid any ground systems at all. As long as aircraft in flight can receive it, that's all that is required. Geosynchronous satellites work, then, and are even preferable because far fewer are required, and they're already there. It just requires leasing some bandwidth on a couple of satellites.

 

I hope to see a WAAS-capable GPS installed in my aircraft before I retire, but I'm very pessimistic about that. They cost too much (~$10,000 for an IFR-certified installation) and provide too little advantage to make it worth spending the money to put new ones in all our helicopters. There just aren't enough precision GPS approaches available in places where we need to land to make it economically viable.

 

You may or may not see improved accuracy with WAAS on or off. It depends on too many factors. In thick woods, you're not likely to be able to pick up the WAAS birds, and often lucky to get even a few GPS signals, so it's pretty useless under those circumstances. If you're hunting a micro in a parking lot, then it may help.

[+NightPilot]

Well, I hit the Post button, got a blank page, refreshed, and got a double post, undeletable.

Edited March 27, 2005 by NightPilot

[+EraSeek]

Yes WAAS was developed for aircraft use, but as with many things it has expanded into other fields. Marine traffic comes to mind, perhaps agriculture as well. At any rate it is not just for aircraft anymore.

 

Here is the accuracy for verticle and horizontal. The first column is non-DGPS and the second is DGPS in meters:

 

"Table 2 Standard error model - L1 C/A (no SA)

 

Vertical one-sigma errors--VDOP= 2.5 12.8 3.9

Horizontal one-sigma errors--HDOP= 2.0 10.2 3.1

 

 

*This is the statistical ranging error (one-sigma) that represents the total of all contributing sources. The dominant error is usually the ionosphere. A horizontal error of 10 m (one-sigma) is the expected performance for the temperate latitudes using civilian (C/A-code) receivers. "

 

So 42' non and 12.8' corrected. 33.46' and 10.17' for horizontal. Not that far off. I found the following statement interesting...something I didn't know before... as I read it these are the usual errors alway in the ionosphere. In other words, even when the ionosphere is calm these are the errors you will see. Of course they can be greater with disturbances.

[+VirginiaJim]

However, it is illogical to assume that WAAS will degrade your accuracy - you either receive it and it ehances accuracy, or you don't receive it and it has no effect.

 

I am not assuming anything. I have merely quoted two sources, and there are others, that state that WAAS can degrade performance in some circumstances. As I have said, I had personal experience with navagation equipment while in the Navy that cost millions of dollars to install and operate. It had limitations and we often experienced system degradation in certain environments. That is part of any technology. We are talking about realtively inexpensive GPS units. WAAS is not a "holy grail." However it is a wonderful technology that will hopefully continue to improve and decrease in cost as our GPS units continue to improve and decrease in cost.

 

We are using a technology that I use often myself. We are using a technology that is improving. However, we are using it in a way which it was not orginally designed for. Most of us are using GPS units that do not come close to the quality or design necessary to take full advantage of the WAAS signal and we are often not in an enviroment that is conducive to its use. We are often not at the end of an airprot runway. We are often not in the middle of an open agricultural field were it is used to control equipment. My brother-in-law has a large farm near Plains GA. He uses WAAS enabled GPS units there.

 

Under these circumstances it is not illogical to assertain the possiblity this technology has limitations and may degrade performance as we use it. Attacking the sources as "boooooooooooooogus!" and "useless outdated data" is not productive and certainly serves no purpose. Yelling the word "FACT" before each statement....

 

Talking, intelligently about the details, such as NightPilot, Eraseek, and philthebottle is productive. Considering the sources and their time frame is helpful. Posting other sources and discusssing them is helpful. I often learn something new about WAAS from their post. I learned many things from NighPilot's post. That is the kind of post that should fill the forums. Intelligent answers and discussions. Not irrational name calling and rude responses.

 

NightPilot, I envy your flying and especially enjoy your avatar. Thank you for your perspective and information.

 

I trust everyone reading or particiapting in this thread will have a good day. I'm going Easter geocaching on another rainy day in central VA. I look forward to learning more.

[+EraSeek]

Under certrain conditions-say, when weak WAAS satellite signals are being received or the GPS receiver is a long way from a ground station-accuracy can actually worsen when WASS is enabled.

 

I found this information in Geocaching for Dummies by Joel McNamara

I'm sorry, but this statement IS boogus and never was true. If you you recieve the WAAS signal weak or not you get the data. Distance from ground stastion is NOT a factor with WAAS, only with regular DGPS.