See also: http://lea.hamradio.si/~s53mv/navsats/theory.html
See also: http://www.aholme.co.uk/GPS/Main.htm
GPS (2022)
11–20 of 36 posts
Re: GPS (2022)
#12GPS satellites don’t correct for relativistic effects. They just set the Earth as the preferred frame, which is a great choice for a terrestrial positioning system. I’ll see if I can find the paper it’s quite interesting. Edit: I can't find the specific paper I'm thinking of. It's one that discusses how when other orbiting bodies want to use GPS they have to make a bunch of complex corrections that terrestrial users…
If you do run across the paper, please post it. It sounds quite interesting.
Re: GPS (2022)
#13See also: http://lea.hamradio.si/~s53mv/navsats/theory.html
The article says that GLONASS time counts days from zero to 1461, then resets back to zero. This is 4 years if we think leap year is once 4 years. But it is not. Leap year is once 4 years, but each 100 years it is not, except each 400 years it is. This is on average 365.2425 days per year not 365.25 days per year. Is GLONASS not long term thinking ahead enough?
Re: GPS (2022)
#14GPS satellites don’t correct for relativistic effects. They just set the Earth as the preferred frame, which is a great choice for a terrestrial positioning system. I’ll see if I can find the paper it’s quite interesting. Edit: I can't find the specific paper I'm thinking of. It's one that discusses how when other orbiting bodies want to use GPS they have to make a bunch of complex corrections that terrestrial users…
I believe there is a correction for the onboard satellite atomic clocks, which run faster than ground/ECI clocks due to a combination of special and general relativistic effects. The correction is a simple one - they just calibrate the clock with a small polynomial. IIRC nothing but the linear and constant terms are even required or used.
Re: GPS (2022)
#15See also: http://lea.hamradio.si/~s53mv/navsats/theory.html
The article says that GLONASS time counts days from zero to 1461, then resets back to zero. This is 4 years if we think leap year is once 4 years. But it is not. Leap year is once 4 years, but each 100 years it is not, except each 400 years it is. This is on average 365.2425 days per year not 365.25 days per year. Is GLONASS not long term thinking ahead enough?
GLONASS also depends on leap seconds, which is why Russia is opposed to eliminating them by 2035.
Re: GPS (2022)
#16Once you understand the theory, you can look at this for actual code and calculations on received GPS data: https://news.ycombinator.com/item?id=35550339
Re: GPS (2022)
#17Ah, from ciechanow.ski, so upvoted instinctively. Only then I realised this is from 2022. Anyway, it's nice to see this post again.
I was hoping this was new as well.
Re: GPS (2022)
#18GPS satellites don’t correct for relativistic effects. They just set the Earth as the preferred frame, which is a great choice for a terrestrial positioning system. I’ll see if I can find the paper it’s quite interesting. Edit: I can't find the specific paper I'm thinking of. It's one that discusses how when other orbiting bodies want to use GPS they have to make a bunch of complex corrections that terrestrial users…
If you do run across the paper, please post it. It sounds quite interesting.
"Relativity in the Global Positioning System" by Neil Ashby of the University of Colorado is excellent. Chapter 6 discusses relativistic corrections for satellites using GPS.
Living Rev. Relativity, 6, (2003), 1
https://link.springer.com/content/pdf/10.12942/lrr-2003-1.pd...
Ashby knows whereof he speaks. He is credited with properly accounting for general relativistic effects in what is now the GPS constellation.
Re: GPS (2022)
#19GPS satellites don’t correct for relativistic effects. They just set the Earth as the preferred frame, which is a great choice for a terrestrial positioning system. I’ll see if I can find the paper it’s quite interesting. Edit: I can't find the specific paper I'm thinking of. It's one that discusses how when other orbiting bodies want to use GPS they have to make a bunch of complex corrections that terrestrial users…
GPS satellites don't compensate for relativistic effects (except for the huge offset built into their atomic clocks), but receivers certainly do. The satellite orbits are slightly elliptical which leads to varying gravitational time dilation. If this is not taken into account, positioning is off by around 10 m [1]. This is an effect from general relativity, so it might be left out in simple textbook explanations.
[1] https://gssc.esa.int/navipedia/index.php/Relativistic_Clock_...
Re: GPS (2022)
#20Earlier quoted context omitted.
The article says that GLONASS time counts days from zero to 1461, then resets back to zero. This is 4 years if we think leap year is once 4 years. But it is not. Leap year is once 4 years, but each 100 years it is not, except each 400 years it is. This is on average 365.2425 days per year not 365.25 days per year. Is GLONASS not long term thinking ahead enough?
GLONASS also depends on leap seconds, which is why Russia is opposed to eliminating them by 2035.
Leap seconds are completely arbitrary by committee, aren't they? I'm curious how there could be a technical dependency.