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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 ...
Too many people, in my opinion too is eager to screan out "Are you completely clueless? Don't you know that ..."
The last week, the victims of such attacks have been those referring to the Corona virus attack as a "flu". "What a fool you are - the Corona thing is NOT a flu!"¨
I didn't know that myself until looked it up in Wikipedia (however reliable that source is ...), learnig of the four classes of "influenza viruses" (or "viri", for those with a classical education). What Wikipedia did NOT explain is why these four classes of viri has been elevated to the sole position of influenzing our health. With a "z". Because the list of symptoms of being influenced (with a "c") by Corona viruses, or a crowd of others, is so similar that even a doctor could not off hand tell that "These are Corona symptom, not influenza symptoms".
I fully understand that influenza is caused by a specific group of viri. What I don't understand is why the effect of this virus group on human health is separate out and labeled "influenza", when other virus groups have very much of the same effects, which are not called "influenza".
Could anyone explain this to a person with next to nothing background in medical theory?
Hopefully with something more informative than "... because they are causes by viri with other signatures"!