EGNOS, please do tell.
- Thread starter shedracer
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Dutchman
Registered user
shedracer said:
Everything you ever wanted to know about EGNOS is here:
http://www.esa.int/esaNA/GGG63950NDC_index_0.html
Cheers
Dutch
Hey Dutch, I read that when I did a search on the web. It says, "EGNOS will become fully operational in 2005. In the meantime, a test signal broadcast by the Inmarsat IOR satellite allows potential users to acquaint themselves with the facility and test its usefulness".
But it doesn`t realy say whether we should be using it now. I guess I`ll just turn it on and see how it goes.
But it doesn`t realy say whether we should be using it now. I guess I`ll just turn it on and see how it goes.
Dutchman
Registered user
shedracer said:
Mmmm.....yes I saw that too.....it's a link I've had on BMW Riders Scotland for a couple of years now....and I just remembered it when you posted.....
On my BMW NavII/2610 I have the latest firmware but it still shows the WAAS rather than EGNOS....
Real big question is, 'how will you know it's working............?'
I'd be interested to hear how you get on.....
Where's Pan European when you need him...........?
Cheers
Dutch
IIRC Pan European said don't bother. Why do you need millimetre accuracy when the mapping isn't that good. Also the WAAS satellite was (is?) too low to be any use unless you're in Pakistan and therefore you'd get better value out of having 12 possible satellites rather than 11.
Plus, the Garmin GPSR's rubber band you to the roads. Makes it interesting if you down load the track afterwards, which is the raw data AFAIK.
YMMV IMHO etc etc
Plus, the Garmin GPSR's rubber band you to the roads. Makes it interesting if you down load the track afterwards, which is the raw data AFAIK.
YMMV IMHO etc etc
PRR
Guest
Please remember that Pan European is echoing Garmin messages and you will have to filter his opinions to have the truth. For a long time Garmin didn't receive the ESTB (EGNOS System Test Bed) signals when other manufacturers did and of course Garmin wouldn't promote enabling EGNOS at that point.John Armstrong said:
First of all EGNOS doesn't give millimeter accuracy. It will get you to about 2 meter accuracy. Normal position errors are larger than most mapping errors and taking one error away is of course always an improvement.
Incorrect again. I received the signal a few hours ago in Sweden far north (thus worse for EGNOS-reception) of the UK. A clear view to the south is all that's needed.
Really, please explain why you need 12 channels? The argument for a high number of channels is to improve accuracy, but since you say you don't need accuracy I don't understand your logic. Also when there are more than 10 satellites present, usually some of them will be as close to the horizon as the EGNOS ones are.
Why not have your tracks improved instead if there's no real disadvantage to having EGNOS enabled? If you have your track frequency set to Auto it will save you a few trackpoints when the track accuracy is improved.
I'm still waiting for a credible explanation to why we can't spare a few channels in a 12 channel-receiver. Until then I find no harm in having EGNOS enabled.
PRR
Guest
Have a clear view of the southern sky and just wait...shedracer said:
Garfieldus
Guest
PRR said:
Hmmmm.... so someone else noticed also
Just an update on EGNOS. I have enabled it since today and have been getting very good results. The best accuracy was 5ft, although EGNOS is not possible all the time. Seems to be well worthwhile enabling it though.
Tip: It does take a while to acquire at first, but since that initial first acquire it been pretty normal.
Tip: It does take a while to acquire at first, but since that initial first acquire it been pretty normal.
PanEuropean
Registered user
PRR said:
PRR:
You think I am just echoing Garmin messages, and you state that I am being less than truthful here? Go jump in a lake.
The only difference between the current GPSR software (that says EGNOS) and the previous versions of GPSR software (that said WAAS) is that Garmin has improved their localization of the user interface, so that Americas GPSRs say WAAS and European ones say EGNOS. It's entirely a cosmetic difference. In theory, all of the GPSRs should say SBAS, but a decision was made to refer to the augmentation systems by the local name used for the augmentation system in each world region.
All of the Satellite Based Augmentation Systems (SBAS, to use the most precise term) follow the same specifications: An augmentation transponder on a commercial satellite - not one of the GPS constellation satellites - broadcasts a correction signal that is received and interpreted by a SBAS capable GPSR. The GPSR then makes the appropriate correction in order to determine receiver position with greater accuracy.
Because the SBAS specification is the same worldwide - for the FAA WAAS system, the ESA EGNOS system, the Japanese MTSAT-2 system, etc., any GPSR that works with one system will work with any other system, provided that the system operator has released full specifications, to allow the GPSR to know where to look for the signal.
I remember spending two months back in the winter of 2004-2005 testing Garmin GPSRs with the EGNOS testbed based out of Zurich. The GPSR picked up the EGNOS signal just fine, as long as the ESA were transmitting the signal. At that time, transmissions were erratic because it was still in test. I have not been in Europe for the past 4 months, so, I can't give you an update on how the system is performing at this time.
You made a few comments in your post above that reveal an incorrect understanding on your part of the basic concepts of the satellite constellation. You wrote:
PRR said:
Let me try to answer your questions, and correct your misconceptions.
1) Geostationary vs. elliptical orbits
The augmentation transponders (SBAS transponders) are carried by commercial satellites that are in geostationary equatorial orbits. The further north you go, the more difficult it will be to receive them in a terrestrial vehicle. However - the further north you go, the less you need augmentation, because the geometry of the conventional GPS satellite constellation is such that you will get the best possible view of the satellite constellation from either the north pole or the south pole. In other words - the closer you get to a pole, thus, the more difficult it becomes to pick up the augmentation satellite - however, who cares, because the closer to a pole you get, the less you need the signal from the augmentation satellite. Think about it.
2) Why do you want 12 channels, not 10?
It's simple. When you are using GPS navigation in a terrestrial vehicle (rather than in a boat, or an aircraft) your GPSR's view of the satellite constellation is continually being interrupted by buildings, trees, and landforms. You only need 4 satellites in view to get a reasonable position fix - that is to say, a position fix that is sufficient for automotive navigation. If, however, your GPSR has the capability of tracking 12 satellites, that means you can lose up to 8 of them at any one time (due to parts of the horizon being obstructed) and still maintain satisfactory tracking.
On the other hand, if you enable the SBAS function, you set aside two of the twelve channels for dedicated tracking of the augmentation satellites. You now only have 10 channels available for tracking the GPS constellation. If you lose more than 6 of those satellites, you will lose your position fix, and, I can assure you, if you lose more than 6 satellites due to terrain, building, or vegetation obstructions, you will also have lost all view of the augmentation satellites as well.
Finally - as has been stated before - the automotive GPSRs are designed to have a magnetic attraction to the charted depiction of the roadway, even if that means making allowances for cartographic errors that might result in the roadway being depicted a few meters away from where it actually is. There's no point in having two meter accuracy on a roadway that it typically 10 or more meters wide, most especially when the GPSR will, by design, discard that accuracy in favour of depicting your vehicle position as 'on the roadway' if there is any question about where you actually are when you are proximate to a roadway.
Kind regards,
Michael
HMR
Registered user
Michael,PanEuropean said:
am I right if I interpret what you are saying this way?
- Enabling EGNOS when using the GPSR in a vechicle on public roads it will not improve the operation of the GPSR.
- Disabling EGNOS will make the function of the GPSR more robust.
And therefore make the following conclusion?
- EGNOS should be disabled when the GPSR is used on a motorbike!
PanEuropean
Registered user
By and large, yes, that is what I am trying to say.
SBAS has the capability of improving the accuracy of the GPSR position fix from a typical average of 7 meter accuracy (unaugmented) to a typical average of 2 meter accuracy (with satellite based augmentation).
For automotive and motorcycle users (note how I stress this), this improvement in precision is of no value whatsoever, because all we need is precision to 15 meters - that being the width of an average roadway. As mentioned earlier, the automotive GPSRs actually discard more precise derived locations if there is any conflict between the calculated location and the 'presumed' location, based on the cartographic data being displayed.
What we, as automotive users, value more than anything else is a continual, steady, uninterrupted position fix. As we travel along, various objects block our reception of satellites, so, we want to have as many channels as possible tracking as many (conventional) satellites as possible, to ensure we always keep at least 4 satellites in view. Hence my recommendation that SBAS be left off for automotive use.
Now, if I was using the GPSR for some other purpose than automotive navigation - for example, to find a cache, or to find a buried cable on a farm field, or to lay out a runway, or something like that - hey, any kind of augmentation I could get to improve positional accuracy would be great. The satellite based augmentation systems will generally give you two meter accuracy. Limited range land based augmentation systems (normally found near airports or marinas) will generally give you 10 cm accuracy, although they require an additional receiver to be attached to the GPSR. Some specialty augmentation systems, such as what John Deere offers for agricultural use, will provide sub-centimeter accuracy. If you are using a GPS system to guide a tractor (running on an autopilot) between row crops, you want as much accuracy as you can get - a 25 cm error means a lot of squashed vegetables. By the same token, if you are out in a farm field spraying or harvesting row crops, the likelihood of your GPSR antenna being obstructed by buildings, vegetation, or terrain as you cruise along at a steady 7 MPH is pretty small, which means that as long as you have half a dozen satellites in view, that's really all you need.
The best analogy to use would be the level of accuracy you need when you calculate fuel mileage on your moto. For a car or a moto, it's good enough to be accurate to the nearest mile (e.g. 25 miles per gallon). Precision beyond that is pointless. If, on the other hand, you were flying a large aircraft on a transAtlantic route, you might want to have a figure that is more precise than '4 or 5 miles per gallon', because the difference would be quite meaningful to you.
Michael
SBAS has the capability of improving the accuracy of the GPSR position fix from a typical average of 7 meter accuracy (unaugmented) to a typical average of 2 meter accuracy (with satellite based augmentation).
For automotive and motorcycle users (note how I stress this), this improvement in precision is of no value whatsoever, because all we need is precision to 15 meters - that being the width of an average roadway. As mentioned earlier, the automotive GPSRs actually discard more precise derived locations if there is any conflict between the calculated location and the 'presumed' location, based on the cartographic data being displayed.
What we, as automotive users, value more than anything else is a continual, steady, uninterrupted position fix. As we travel along, various objects block our reception of satellites, so, we want to have as many channels as possible tracking as many (conventional) satellites as possible, to ensure we always keep at least 4 satellites in view. Hence my recommendation that SBAS be left off for automotive use.
Now, if I was using the GPSR for some other purpose than automotive navigation - for example, to find a cache, or to find a buried cable on a farm field, or to lay out a runway, or something like that - hey, any kind of augmentation I could get to improve positional accuracy would be great. The satellite based augmentation systems will generally give you two meter accuracy. Limited range land based augmentation systems (normally found near airports or marinas) will generally give you 10 cm accuracy, although they require an additional receiver to be attached to the GPSR. Some specialty augmentation systems, such as what John Deere offers for agricultural use, will provide sub-centimeter accuracy. If you are using a GPS system to guide a tractor (running on an autopilot) between row crops, you want as much accuracy as you can get - a 25 cm error means a lot of squashed vegetables. By the same token, if you are out in a farm field spraying or harvesting row crops, the likelihood of your GPSR antenna being obstructed by buildings, vegetation, or terrain as you cruise along at a steady 7 MPH is pretty small, which means that as long as you have half a dozen satellites in view, that's really all you need.
The best analogy to use would be the level of accuracy you need when you calculate fuel mileage on your moto. For a car or a moto, it's good enough to be accurate to the nearest mile (e.g. 25 miles per gallon). Precision beyond that is pointless. If, on the other hand, you were flying a large aircraft on a transAtlantic route, you might want to have a figure that is more precise than '4 or 5 miles per gallon', because the difference would be quite meaningful to you.
Michael
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