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originally posted by: Nochzwei
a reply to: kruphix
submitting a paper to a science journal will happen in the future.
but the MO exhibited by all the ats dimwits was hilarious, to say the least. was fun while it lasted.
have a nice day everyone
wtf are you on about mate? pl elaborate
originally posted by: Phage
a reply to: verschickter
No. It goes beyond that.
While it is true that the satellites transmit a time of day timestamp which our receivers use to tell us what time it is, there's a problem. There is a lightlag between the time the satellite sends that packet and the time it gets to you. The satellites are at different distances from you. So, which satellite do you believe because the lightlag for each will be different and what is used in calculating position is the relative lag between satellites, not the lag between a satellite and the receiver.
A satellite says, "the time now is 0.0" but when the receiver gets it the time actually 0.001 (for example) because of the time it takes for the signal to reach it.
But what about the satellite which is farther away? It says, "the time is now 0.0", but when the receiver gets the signal, it is now 0.0015.
See the problem? While you can get a time of day that's pretty good for getting somewhere on time, you cannot get enough accuracy for the positional calculations to get you "there" with a high degree of accuracy. That is why the clock time (time of day) is not used for positional calculations. That is why the relative time lags between satellites is used, that is why the actual time of day is not necessary for the calculations. If the clocks on the satellites were running at a different rate than those on the receivers, no joy.
What having a fairly accurate time of day gives you (your GPS receiver that is) is the ability to know where to look for the satellites, based on their ephemerides (which are periodically updated). It means you don't have to search the whole sky each time you turn your GPS on.
That's what selective availability was about, it sent a jiggered "0.00" which civilian receivers had no way to decode. One of the best things Clinton did was end that.