WAAS...do You Really Need It?

[+Cache Viking]

I had a Garmin III+ and replaced it with a V. With the V I have had the WAAS on since I bought it. When I go hiking I tend to leave the GPSr on since my family likes to look at the track logs. I guess I need to go out and time how long it takes to get a WAAS lock and as to the accuracy and then again without WAAS. Will try to do that this weekend and post a followup. I also use lithium batteries and seem to get plenty of life out of them so I can't say I have had a battery drain problem like I did with alkaline batteries. I would go to rechargables but remembering to charge them is a problem so I continue to use lithium.

[+OKThumper]

So I get two guys punching each other out over crud and I feel like closing the thread just to stop the abuse, then somebody comes along with a positive post that makes me want to keep it open. We all (including the lurkers) are trying to glean little bits of knowledge out of the reading of these boards, threads, and posts. In that light lets see if we can share our collective knowledge without being abusive or for that matter so defencesive. My boss, and good friend, once told me to look at the importance in ten years of the issue at hand, then treat it accordingly at this time. I think that may be good advice. So keep the good applicable information coming, and a little humor does not hurt either.

 

Thumper

 

PLAY NICE

Edited February 10, 2004 by OKThumper

[+gbod]

Like the energizer bunny, this thread keeps going and going...

 

Actually I do have a legitimate question that I have not seen an answer to...

 

On this webpage about WAAS, it has a map of the WAAS ground stations:

 

with this statement below the map:

WAAS coverage is approximately 200nm around these stations

 

So, my question is a two part question:

# 1: Where exactly are the WAAS ground stations? (I mean I can see on the map where they are, but does anyone know exactly the cities or coordinates for the stations?)

 

And #2 It says the coverage area is 200nm around these stations. Can I assume then that if I am beyond 200nm from any of these stations (which I think I am in southwest Idaho) that having your WAAS enabled really does not improve GPSr accuracy?

[+PDOP's]

So, my question is a two part question:

# 1: Where exactly are the WAAS ground stations? (I mean I can see on the map where they are, but does anyone know exactly the cities or coordinates for the stations?)

 

And #2 It says the coverage area is 200nm around these stations.  Can I assume then that if I am beyond 200nm from any of these stations (which I think I am in southwest Idaho) that having your WAAS enabled really does not improve GPSr accuracy?

#1 The only place I've ever seen these listed was in a posting to the GPS Newsgroup

 

#2 The Stanford Uninversity site also states that the nominal separation of reference staions is between 500 and 1000(km) implying that 500(km) radius might be the distance beyond which system is unable to generate corrections. However if you look at this display of FAA Vertical Protection Limits which includes most of Canada in the service area indicating that the limiting distance might be fairly generous. Note that the vertical accuracy of a GPS fix is

commonly stated as half the horizontal (vertical error is double)

 

Edit : The Stanford University link appears to be dead at the moment. I'll try and update it when i can find it.

Edited February 10, 2004 by PDOP's

[+GEO*Trailblazer 1]

Here is what I have found so far.

 

Master Control Station is here

 

5 Monitor Stations are here

 

Scroll down to Ground Control Stations

Edited February 11, 2004 by GEO*Trailblazer 1

[+ifconfig]

Here is what I have found so far.

 

Master Control Station is here

 

5 Monitor Stations are here

 

Scroll down to Ground Control Stations

What do those links have to do with WAAS ground stations?

[+EraSeek]

"The WAAS provides augmentation information to GPS/WAAS receivers to enhance the accuracy and reliability of GPS position estimates. The signals from GPS satellites are received across the NAS at many widely-spaced wide area reference stations. Each reference station relays the information, via a terrestrial communication network, to WAAS wide area master stations. The master stations use the information collected by the reference stations to develop corrections to the GPS position information. These corrections are sent to a ground uplink station where they are transmitted in the form of a WAAS correction message to a Geostationary Earth Orbit (GEO) satellite. These GEOs broadcast the WAAS message to users across the U.S., and portions of Alaska, on the same frequency as GPS. The WAAS broadcast message improves GPS signal accuracy from 20 meters to approximately 1.5 - 2 meters in both the horizontal and vertical dimensions"

 

If you want to understand WAAS, think of it as a net cast across the whole of the US. It is not dependent to any great degree on how far you are from a ground station. If you are in the US you are covered. Ground station, as stated above, collect signals from the GPS sats. The errors in the signals are analized and 'modeled' as a whole across the whole coverage (US) area. It turns single data points into a blanket of data points and fills in the logical blanks in between. It 'models' the coverage area. These delays in signals and timing errors are turned into a correction net. This correction almanac is sent from the master stations to the GEO sats. Your GPS gathers the almanac, figures out where you are in that net by triangulating the nearest correction points in that virtual net, and applies the apropriate corrections. Your GPS is an intrigal part of this system. Being closer to a ground station will only have a very, very, slight benefit, unlike regular DGPS. The important thing is that you are in the correction coverage area. That being the US and a bit more (some of Canada).

 

I've seen another site that show the location of ground stations. I'll see if I can find it. Not that it matters that much.

[+GEO*Trailblazer 1]

WASS this it?

 

Scroll down to WASS

 

link is

www.garmin.com/aboutGPS/wass.html

 

but it will not link through this site.

Edited February 11, 2004 by GEO*Trailblazer 1

[+EraSeek]

No. Can't find it right now. I'll look some more tomorrow. This was a map which showed which and what type of station was where. I remeber on uplink station was in Brewster Washington.

[+GEO*Trailblazer 1]

I hope this is not one of them as some would say a .a.a.a.a well here is another cool link.

 

Trimble tutorial

 

then in the same place under CIVILIAN COMPANIES IS A DISCLAIMER THAT WE WOULD HAVE TO KILL YA IF WE TOLD YA.

HERE

[+gbod]

...It is not dependent to any great degree on how far you are from a ground station...

...The errors in the signals are analized and 'modeled' as a whole across the whole coverage (US) area. It turns single data points into a blanket of data points and fills in the logical blanks in between. It 'models' the coverage area...

...Being closer to a ground station will only have a very, very, slight benefit, unlike regular DGPS. The important thing is that you are in the correction coverage area. That being the US and a bit more (some of Canada).

Thanks for your response. You answered my question quite well.

[+OKThumper]

Just the right kind of stuff, and the reason I have not closed this thread, thank you EraSeek for your post.

 

GEO what the hell are you on now what does a.a.a.a. and civilian company disclaimers have to do with the subject of this thread? I guess I missed the point or the humor in it. Next you will want to quote the price of tea in China, or something. Just bustin your chops GEO. Go for it.

 

Thumper

[+OKThumper]

Geo: I went through the Trimble Tutorial thing, lots of good info to be had in there, it finally mentioned WAAS WAAY into the show, but did not mention much about its usefullness in our application. Thanks for the link.

 

Thumper

 

 

 

This is a Pseudo Random Post, I just loved the Pseudo Random Code thing.

[+EraSeek]

Actually, I thought the Trimble tutorial was on of the best and most complete I've seen. The other link about dual frequency, as I understand it, is the newest idea that uses satellite (2 frequency) signals directly to determine errors and make corrections, by passing the whole ground station thing (I think). Kerry know a lot more about this stuff.

 

This is how I think it works. By broadcasting two differing frequencies you can determine the errors caused by ionospheric disturbances by the differences in the receipt of those signals. If conditions were perfect those signals should be received at the same time, but because of the difference in frequencies, they know that one frequncy will pass through the disturances less effected than the other type of frequency. You just need two check the error in the two and apply the correction which would already be in your firmware. No huge exspensive WAAS system nessecary, just a GPS unit that can handle this type of signal. Just conjecture, a guess on my part, but I think it is something like that.

Edited February 12, 2004 by EraSeek

[+EraSeek]

By the way, I suspect the ground station map I was looking for may have been in the old Trimble tutorial.

Also by the way, HERE is a ball cap from Trimble that has a pocket in it so you can put your attachable antennea in it and get a good signal whils irraditating your head.

[Kerry.]

EraSeek, dual frequency isn't really the same thing as Wide Area Differential GPS (WADGPS). For sure the second freq allows some of the errors to be resolved in real-time but one still needs some form of accurate reference mark to get a similar accurate position within some reasonable distance and the distance basically dictates the time required and/or accuracy achievable from real-time differential or static differential.

 

Actually the commercial Satellite Based Wide Area systems, which do use dual frequency gets much better accuracy than say WAAS but at the cost of no integrity. WAAS uses a lot of bandwidth applying integrity and monitoring to the position, which basically then restricts remaining bandwidth to using L1 but at a cost.

 

Really every thing is a compromise, cost, distance, accuracy, integrity, coverage, simplicity etc etc.

 

Many in fact often wonder if the dollar cost per each additional metre from WAAS is actually good accounting. Many countries are implementing other augmentation type systems as simply the cost of WAAS/EGNOS type systems is extremely prohibitive.

 

Give things a few years when enough Block IIR-M's and IIF's are in orbit a new handheld (of course) and around 1.5 metres will be the accuracy of the day, un-augmented, stand-alone.

 

Cheers, Kerry.

Edited February 12, 2004 by Kerry.

[+EraSeek]

OOps. Hey Kerry, I just edited my above post guessing at how the Duel Frequency works. Was I right about one signal having more delay than the other?

[+GEO*Trailblazer 1]

CONTROL POINT, *ACCURATE REFERENCE POINT*

VECTOR ANALYSIS *THE POINTS IN BETWEEN *.

 

NOW IF YOU HAVE A (GEOID)*TRIANGLE* PLACED ON THE GROUND ,WITH CONTROL POINTS OF 1ST DEGREE ORDER AND YOU THEN NAVIGATE WITHIN THAT PERIMETER YOUR READING ARE VERY ACCURATE.

MY EXPERIENCE PINPOINT..........

 

THAT IS BY CALCULATING THE DISTANCES FROM THE SEVERAL POINTS,WHICH YOUR GPS IS DOING AS WELL.AND YOU CAN USE A COMPUTER TO GET IT EVEN CLOSER.

IT IS NOT JUST THE GPS IN ACCURACY,LIKE STATED THERE ARE MANY NUMEROUS FACTORS USED TO CALCULATE.

 

I GUESS LINKS WILL NOT SUFFICE THE STUDY, SO I WILL JUST PUT IT INTO MY OWN WORDS OF WHAT HAS ALREADY BEEN COVERED IN ALL THE PREVIOUS POSTS.

 

I AM NOT YELLING JUST SPEAKING UP.

 

I DO NOT LIKE TO BE CRITICIZED OR CRITIQED BY THOSE WHO WILL NOT POST WHO THEY ARE AND WHAT THEIR AUTHORITY IS!

I HAVE AND AM A DISABLED MEASURMENT TECH.

 

WHAT ARE YOU HIDING?

[Kerry.]

EraSeek, yeah basically that's what dual freq allows, determination of atmospheric issues in real-time rather than using a modelled type atmosphere as is applied if one is only using L1. L1 C/A (Course Acquisition code) is available to all users and has a very long wavelength (~300 metres), which a very short sequence (fraction of a second) and continues to repeat itself over and over again. The P (precise) code, which is carried on both L1 & L2 has a wavelength of only about 30 metres but the code sequence lasts something like nearly 300 days before it repeats itself. Until recently L1 C/A (the one we use) was required to resolve/initialize the P code but now they've apparently found a way to shutdown L1 and use L2 Pcode by itself.

 

Basically we (the public) don't currently have full access to a compete second frequency but that is about to change. Survey type receivers achieve accuracy using differential positioning (requires more than 1 receiver) and squeezes millimetres into the measurements using carrier wave phase measurements.

 

So with the new second civil frequency accuracy will improve and with that there is also some new additional military frequencies.

 

Basically the above has little to do with WAAS as WAAS only uses L1 simply because it requires the remaining bandwidth to carry the integrity information/messages and doesn't have time (time being the critical factor in WAAS error messages) to also do things with phase measurements. For the purpose of WAAS the integrity/monitoring and timely transmission of error messages takes precendence over the accuracy, with accuracy basically not being the primary function.

 

Cheers, Kerry.

Edited February 12, 2004 by Kerry.

[Keystone]

So I get two guys punching each other out over crud and I feel like closing the thread just to stop the abuse, then somebody comes along with a positive post that makes me want to keep it open. We all (including the lurkers) are trying to glean little bits of knowledge out of the reading of these boards, threads, and posts. In that light lets see if we can share our collective knowledge without being abusive or for that matter so defencesive. My boss, and good friend, once told me to look at the importance in ten years of the issue at hand, then treat it accordingly at this time. I think that may be good advice. So keep the good applicable information coming, and a little humor does not hurt either.

 

Thumper

 

PLAY NICE

OKThumper has done a fine job of moderating his own thread, so I haven't jumped into this one previously.

 

This topic long ago surpassed the usual scope of what is discussed in the "Getting Started" forum. It is fine for the discussion to continue for so long as it remains positive, on-topic, and free of interpersonal debates. Otherwise, either OKThumper or I will close it.

[+beckerbuns]

I DO NOT LIKE TO BE CRITICIZED OR CRITIQED BY THOSE WHO WILL NOT POST WHO THEY ARE AND WHAT THEIR AUTHORITY IS!

I HAVE AND AM A DISABLED MEASURMENT TECH.

 

WHAT ARE YOU HIDING?

 

What are you on about?

 

[+tsiya]

Just think of it, I joined this group because I was confused! Good Golly, Miss Molly! Let's put it this way, if You guys see Me running around in the woods with no WAAS on, are You going to point and snicker? If You are lost, will You say on Your radio, "don't send Bob to find Me, He has no WAAS, will never find Me before My Right Guard stops working"? I just wanna be socially acceptable, will My crummy old Ebay units (Old Yeller and a Magellan 2000) make the grade? I can't see Your crummy micro containers most of the time, anyway. Just want to get close enough to say I tried.

 

PAINT THOSE COTTON PICKERS ORANGE!!!

Edited February 13, 2004 by tsiya

[+Go JayBee]

Mmmmmmmmmmmmm........WAAS

[+GEO*Trailblazer 1]

I WASS wrong,

I apologize for the venting.

You know what you know,

and let the rest go.

[Keystone]

I meant what I said,

and I said what I meant.

And because you behaved,

you're at zero percent.

[+Cache Viking]

I had a Garmin III+ and replaced it with a V. With the V I have had the WAAS on since I bought it. When I go hiking I tend to leave the GPSr on since my family likes to look at the track logs. I guess I need to go out and time how long it takes to get a WAAS lock and as to the accuracy and then again without WAAS. Will try to do that this weekend and post a followup. I also use lithium batteries and seem to get plenty of life out of them so I can't say I have had a battery drain problem like I did with alkaline batteries. I would go to rechargables but remembering to charge them is a problem so I continue to use lithium.

I went out in my backyard this morning with my Garmin V to compare acquisition times with WAAS enabled and disabled. I found little to no change with WAAS enabled or disabled for acquisition times for satellite numbers below 33. There were only two satellites numbers listed on the screen from 33 and higher which according to the Garmin V manual are WAAS satellites which carry the WAAS correction signals. After 15 minutes I gave up and turned the unit off as the indicator reflecting WAAS corrections never came on.

 

As for ground stations used for correction I believe you are referring to DGPS which requires extra equipment. The WAAS signal is using certain satellites along with extra calculations to refine your position. Maybe someone else can clarify this part.

[Kerry.]

Viking, allowance for only 32 GPS satellites, above 32 they will be something else. There's allowance for 19 WAAS Geo's and even though some manufacturers use the next 19 slots as identifiers 33 thru 51 the WAAS geo's do have proper PRN numbers. The 2 WAAS geo's are PRN 122 & PRN 134, which Garmin ID as 35 & 47.

 

WAAS has and requires physical ground stations just as dGPS requires ground stations but WAAS uses some of the GPS channels for reception whereas dGPS requires a beacon receiver (if not built-in).

 

The satellites that the WAAS corrections are being transmitted through are simply communication satellites leased for the purpose and a WAAS geo may also be used in determining the position solution if activated as part of the navigation message.

 

Cheers, Kerry.

[+Cache Viking]

Viking, allowance for only 32 GPS satellites, above 32 they will be something else. There's allowance for 19 WAAS Geo's and even though some manufacturers use the next 19 slots as identifiers 33 thru 51 the WAAS geo's do have proper PRN numbers. The 2 WAAS geo's are PRN 122 & PRN 134, which Garmin ID as 35 & 47.

 

WAAS has and requires physical ground stations just as dGPS requires ground stations but WAAS uses some of the GPS channels for reception whereas dGPS requires a beacon receiver (if not built-in).

 

The satellites that the WAAS corrections are being transmitted through are simply communication satellites leased for the purpose and a WAAS geo may also be used in determining the position solution if activated as part of the navigation message.

 

Cheers, Kerry.

Thanks. I figured there must be more to what the owners manual said. I went through all my Surveying books but this GPS stuff has come into the surveying arena well after most of them were purchased.

 

Again thank you.

[+Cache Viking]

Viking, allowance for only 32 GPS satellites, above 32 they will be something else. There's allowance for 19 WAAS Geo's and even though some manufacturers use the next 19 slots as identifiers 33 thru 51 the WAAS geo's do have proper PRN numbers. The 2 WAAS geo's are PRN 122 & PRN 134, which Garmin ID as 35 & 47.

 

WAAS has and requires physical ground stations just as dGPS requires ground stations but WAAS uses some of the GPS channels for reception whereas dGPS requires a beacon receiver (if not built-in).

 

The satellites that the WAAS corrections are being transmitted through are simply communication satellites leased for the purpose and a WAAS geo may also be used in determining the position solution if activated as part of the navigation message.

 

Cheers, Kerry.

Thanks. I figured there must be more to what the owners manual said. I went through all my Surveying books but this GPS stuff has come into the surveying arena well after most of them were purchased.

 

Again thank you.

Went out in back yard again today to try again and see if acqusition times were any different. Only change was no cloud layer.

 

I got a Differential Lock accross the screen within 2 minutes. Accuracy improvement was 8-10 vs 15-20. Without WAAS on accuracy was 12-20.

 

Enough for me. I am going to continue to leave it in WAAS setting.

[+GeckoGeek]

Accuracy improvement was 8-10 vs 15-20. Without WAAS on accuracy was 12-20.

At the risk of prolonging a sometimes painful subject, could you repeat that test at a known point such as a triangulation station and report that the actual accuracy is instead of what the unit claims it's accuracy is?

 

Also take a reading over some period of time. The other complaint about WAAS is that some people feel that it leads to more "motion" even though the unit is siting at a fixed point.

 

I suspect that most people would feel more comfortable with a stable point that was accurate to 15-20 feet then with one that kept wondering around, but was always within 8-10 feet.

[+EraSeek]

Accuracy improvement was 8-10 vs 15-20.  Without WAAS on accuracy was 12-20.

At the risk of prolonging a sometimes painful subject, could you repeat that test at a known point such as a triangulation station and report that the actual accuracy is instead of what the unit claims it's accuracy is?

 

Also take a reading over some period of time. The other complaint about WAAS is that some people feel that it leads to more "motion" even though the unit is siting at a fixed point.

 

I suspect that most people would feel more comfortable with a stable point that was accurate to 15-20 feet then with one that kept wondering around, but was always within 8-10 feet.

"some people feel that it leads to more "motion" even though the unit is siting at a fixed point."

 

Now this is an interesting NEW myth. Where are people getting this from? This is the second time I've seen this (and lately). It is simply bunk.

 

Your first point about a fix point (benchmark) is a good one, and I would recommend it too.

[Kerry.]

Maybe accuracy needs to be defined as to exactly what accuracy is.

 

Cheers, Kerry.

[+GEO*Trailblazer 1]

Acurracy, Precision and Errors

 

To Keep us all on the same page.

 

In dealing with measurements it is important to distinguish betwenn accuracy and precision.

as stated by Kerry.

 

As defined by the American Society of Civil Engineers,accuracyis "absolute nearness to the truth" whereas precision is "relative or apparent nearness to truth."(Formerly ASCE defined precision as "degree of fineness to reading in a measurement,or,the number of places to which a computation is carried.")

As defined by the U S Coast and Geodetic Survey,accuracyis "degree of conformity with a standard" whereas precisionis "degree of refinement in the performance of an operation or in the statement of a result."From these mutually consistant definitions it follows that a measurement may be accurate without being precise,and visa versa.

This was quoted out of the

5th edition of

SURVEYING,

Theory and Practice,

Davis

Foote

Kelly

 

McGraw- Hill

[+Cache Viking]

Acurracy, Precision and Errors

 

To Keep us all on the same page.

 

In dealing with measurements it is important to distinguish betwenn accuracy and precision.

as stated by Kerry.

 

As defined by the American Society of Civil Engineers,accuracyis "absolute nearness to the truth" whereas precision is "relative or apparent nearness to truth."(Formerly ASCE defined precision as "degree of fineness to reading in a measurement,or,the number of places to which a computation is carried.")

As defined by the U S Coast and Geodetic Survey,accuracyis "degree of conformity with a standard" whereas precisionis "degree of refinement in the performance of an operation or in the statement of a result."From these mutually consistant definitions it follows that a measurement may be accurate without being precise,and visa versa.

This was quoted out of the

5th edition of

SURVEYING,

Theory and Practice,

Davis

Foote

Kelly

 

McGraw- Hill

Great book. Mine is like the 3rd or 4th edition and missing from my office shelf.

 

The comment about benchmarking in a previous post too is good and I should have done more. All I did so far was to use the exact same spot in the yard at the same time for the same amount of time on different days.

 

The City I live in has just recorded a new Record of Survey updating the Survey Grid that controls our GIS data. This is the grid all work done within our City Limits by City Ordinance has to be tied to. The control points that it is built from are USGS Control Points. Therefore I can use one of the points, list it and then the results of subsequent measurments. Not sure when I will get the time to do this or if it is worth all the trouble since there are a number of factors involved for each GPSr.

 

Until then the following reading may help. GPS WAAS ACCURACY

 

This is one of those questions where there may be no perfect answer for each person, their equipment and location.

Edited February 15, 2004 by Cache Viking

[+GeckoGeek]

"some people feel that it leads to more "motion" even though the unit is siting at a fixed point."

 

Now this is an interesting NEW myth. Where are people getting this from? This is the second time I've seen this (and lately). It is simply bunk.

It was something I picked up in a prior technical decussion on WAAS. And having tried both WAAS on and off, I think I'm seeing the same thing. Everything is fine until you try monitoring a reading over a period of a few minutes or try getting within that last 10 feet of "ground zero" and end feeling like you're chasing a moving object.

 

Before condeming something as a "myth" I would suggest finding out not just WAAS theory, but just how WAAS is actually implemented in popular handheld units. After all, there is no idea so good that a bad implementation can't mess it up.

 

It's been suggested that Garmin doesn't have the best implementation of WAAS. It may not be applying default atmospheric correction if it's not able to get that correction factor. (WAAS has several corrections in it. Some are global, some require that you be within a given distance of an observation station.)

[+NightPilot]

link is

www.garmin.com/aboutGPS/wass.html

 

but it will not link through this site.

 

Maybe it won't link because you're misspelling WAAS. The URL you did post won't work, either, because of the misspelling.

[+EraSeek]

Everything is fine until you try monitoring a reading over a period of a few minutes or try getting within that last 10 feet of "ground zero" and end feeling like you're chasing a moving object.

 

With or without WAAS, when you begin expecting consistant accuracy and stability within the last 10 feet, you are expecting too much, unless it is a professional grade unit. And these units depend on optimal times.

 

However, perhaps "Bunk" was a bit strong. There is a simple way to test this. I took my first stab at it tonight but conditions were too good and little or no correction was being applied. I had 7.2' - 7.4' accuracy reading with WAAS both on and off and virtually no static movement either way.

 

Likewise, I have tested WAAS on my own while standing on known points before and noticed no significant wander over non-Waas. But then again I wasn't really looking for that at the time.

[+EraSeek]

It may not be applying default atmospheric correction if it's not able to get that correction factor.

It will not apply the default corrections, but this os only for the first few minutes. This is why you see the accuracy reading jump way up for a bit, while it is loading the almanac, bit then it soon does and the reading drops significantly when corrections are needed.

[+EraSeek]

(WAAS has several corrections in it.  Some are global, some require that you be within a given distance of an observation station.)

I think I discussed this above earlier. Yes, some of the errors require the input of the observation stations and some don't, but you are over-emphisising the part about the distance from a ground station. There is coverage enough as long as you are in the modeled area. (Most of the US).

 

By the way, I see you are in Hawaii (or seems so) and from what I understand there is a single reference station there, and a bit of a different situation. I assume it works a bit more like regular DGPS, which should do you well at any rate.

Edited February 16, 2004 by EraSeek

[+EraSeek]

Actually I do have a legitimate question that I have not seen an answer to...

 

On this webpage about WAAS, it has a map of the WAAS ground stations:

 

with this statement below the map:

WAAS coverage is approximately 200nm around these stations

 

So, my question is a two part question:

# 1: Where exactly are the WAAS ground stations? (I mean I can see on the map where they are, but does anyone know exactly the cities or coordinates for the stations?)

 

And #2 It says the coverage area is 200nm around these stations. Can I assume then that if I am beyond 200nm from any of these stations (which I think I am in southwest Idaho) that having your WAAS enabled really does not improve GPSr accuracy?

Sometimes the technical info you find on the web can seem to conflict. Here is a quote that points out the independence of the modeled coverage from ground stations distance.

 

"Ionospheric Corrections:

The IONO information transmitted by the WAAS system is much more accurate than the basic GPS IONO model. Also, the WAAS system will generally be more accurate than beacon based DGPS because of the way the corrections are rendered by the WAAS system and applied by the GPS receiver. The primary factor is spatial decorrelation, which is the degradation of corrections due to separation from the reference station. RTCM based DGPS corrections suffer from spatial decorrelation, but WAAS corrections do not.

 

This Iono data (and other corrections) are constantly uploaded to the Geo Sats for re-transmission to GPS navigation receivers. There is no interpolation between ground stations by the receiver. This is because the WAAS master system computes a "grid of Iono corrections" which are location dependent based on the user's position. There is an interpolation/extrapolation process to determine the iono correction, but it is not specifically related to the location of ground stations that collect the information. The Iono-corrections grid offered by WAAS are interpolated and applied by the receiver.

 

GPS receivers must then apply the data for corrections appropriate at their location. This may take five or ten minutes to complete in a typical receiver. "

[+GEO*Trailblazer 1]

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.

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

 

Just some of the model that is well over 20 years in the making now.

sometime math is frustrating to explain in emperical formulas

 

eraseek you said a bunch there thanks