robD said:
You're receiving corrected differential (the D!) data from an EGNOS satellite (in Europe, WAAS in the US, and GLONASS in the former Soviet republics)
Hi Rob:
The first part of your statement is correct, but the last bit of info in the parenthetical remark is incorrect.
WAAS (Wide Area Augmentation Service) and
EGNOS (European Geostationary Navigation Overlay Service) are two implementations of what is referred to generically as
SBAS (Satellite Based Augmentation Service). But - SBAS only augments the satellite navigation system that is operated by the US Military - the system known as
GPS (Global Positioning System). The
GLONASS system is an entirely different satellite based navigation system that is operated by Russia (before that, the CIS, and before that, the CCCP). It is possible that there is some kind of augmentation system for GLONASS, however, if there is, it won't be of any use to those of us who use the GPS (American military) system.
Here's a quick decoder for the alphabet soup of acronyms:
Satellite Based Navigation System
There are two systems that I know of, the system operated by the US Military (known as GPS), and the system operated by the Russian military (known as GLONASS). Although the two systems are very similar in concept, they are not compatible with each other. It's just like cell phone systems in the USA - you can have a GSM phone, or a CDMA phone - they both look the same, but the GSM ones won't work on the CDMA networks and vice-versa.
GPS is actually a 'brand name', not a generic term. The problem is that many people use the US Military name for their system (GPS) as a generic term for all satellite based navigation systems - kind of like using the word 'Kleenex' to refer to facial tissue.
The GLONASS system has never achieved any consumer market penetration. A few years ago, some companies that made aircraft navigation systems offered systems that would listen to both the GPS satellite constellation and the GLONASS satellite constellation, but no-one was willing to pay the extra money for such a 'belt and suspenders' system, so, the avionics companies gave up on that.
Just to confuse matters even further - the EC is in the process of starting up their own satellite based navigation system, which will be called
GALILEO. This is going to be the biggest commercial flop since Motorola just about went bankrupt putting up the Iridium satellite phone system. Heck, if the Americans are already offering their service (GPS) free of charge, who is going to want to pay for an identical service that only covers Europe? Your tax money at work...
Satellite Based Augmentation Service (
SBAS)
SBAS is the correct generic term to describe any system that augments (=corrects minor localized errors) in the American mulitary (GPS) satellite navigation constellation. Both WAAS and EGNOS are examples of SBAS. The Japanese also operate a SBAS, and the Indians are working on getting one operational as well.
SBAS systems are very simple - here's how they work: You go buy a GPSR, and mount it on a cement plinth somewhere, such that it will never move. You then monitor where that GPSR tells you it is, and note the errors that it makes (e.g. 5 feet too far north, 8 feet too far west). Then, you send the error information up to a simple, el-cheapo transponder that you rent on a plain old commercial satellite (just like Sky TV), and that el-cheapo transponder sends out a message to all the GPSRs on motorcycles in the area, advising them of the error that exists at the moment. The GPSRs on the motorcycles then apply the appropriate correction to the position that they have calculated by listening to the satellites in the GPS constellation.
There are other forms of augmentation systems - for example, local differential augmentation that is used by mariners, and if you want, you can even buy your own augmentation system (for about $3,000) and set it up in your back yard. Farmers in America frequently operate their own augmentation systems to allow them to achieve centimeter accuracy (yes, centimeter) when planting, fertilizing, and harvesting crops.
Oh, by the way - Ovenpaa, your software is out of date. If you had the latest software, it would say 'EGNOS', not 'WAAS'. The most recent software is smart enough (and politically correct enough) to know which side of the ocean it is on, and use the correct local word when referring to SBAS.
Michael
