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What I meant was that C++ overloads breakitself, although I suppose this can be debated. But it's annoying not to be able to exit a loop using break when inside a switch statement that's embedded within that loop.
Gallileo is emerging as an alternative to GSM. Being a newer implementation of the same working principle, they provide higher precision.
I have nowhere close to an understanding of how Gallileo (/GSM) positioning works. So when a collague of mine claimed that a precision of one meter on earth requires that the position of the satellites are determined with a precision of one meter (or preferaby better). If you are triangulating between three signals, and some astronauts were out there and pushed each of the three satellites one meter to the south, your Gallileo (/GSM) reading would be 1 meter wrong.
From simle high school geometry, this argument sounds very plausible. But is it really true, that meter and sub-meter precision location is dependent on a similar precision positioning of the satellites?
(Obviously, if you have signals from several satellites, you may do some smoothing to correct for a single off-position satellite. The question is whether the precision of the positioning directly depends on the satellite positioning, on the same scale.)
You are asking about the Gallileo positioning system, I presume?
The European Union has an agency called the European GNSS Agency[^]. The satellite network was set up by the European Space Agency in cooperation with the EU, but ESA is a separate organization, not tied to the EU, and I don't know if they have any sort of ownership to Gallileo.
As far as I (partly, and probably wrong) understand it, it is more the way the signal speed, how long it takes to get from the satellites to your device with a precise clock, that will determine the precision of the position.
No - the accuracy of the satellite position is very important. Yes - the algorithm basically does do ranging using the contents of the GPS message (precise clock and position - the receiver then uses its clock to integrate multiple signals to determine its position on earth) as well as using phase of the signal to further increase accuracy. Using dual frequency allows for cancellation of a lot of atmospheric noise in the signal as well (for higher end dual frequency receivers).
The current GPS satellites are usually positioned to < 1m although they are not guaranteed to be that accurate (I think it is somewhere around 7 meters). If you post process the data using updated ephemeris (orbital positions) you can reduce that even further.
As for Galileo - well I have been waiting for it for 30 years now...
the satellites first have to find their own individual position relative to fixed/known Earth fixed location beacons? Whitehouse is A, Pentagon is B, Al Gores house is C ... triangles, signal time, blah blah: I am here! Yeah stuff on Earth moves about too, so throw in a D, E, F ... it'll figure out what moved. (As long as someone doesn't shove all the beacons 1m to the left position should be pretty close.
The same way 2 or more satellites pinpoint your unknown location they first each pinpoint themslves based on Earth bound reference locations. (Vantage gives them line of sight to many.)
Same as someone called you looking for directions, you look around, "I'm at Billies Bar opposite the Post Office, where are you?" Them, "I'm at ..." You (knowing they can't see BB or the PO), "OK, head north on xx..."
Accuracy, yeah latency, atomic clocks ... still going to be air temperature [layers], clouds, even where the Sun is and what mood it's in at the time - the more [pref closer] points it can reference the more it can defactor a lot of that too.
Apparently one of the hardest things to fix is the satellites wobbling. Yeah they got gyro's and all that, but slow wobbles (thrown in harmonics...) are hard to measure while still discounting sensor noise and ...