- It gets even more interesting if you take into account how the satellites know where they are. Around the world there are fundamental stations: https://en.wikipedia.org/wiki/Fundamental_station
I had the opportunity to visit one. Basically they measure their own position in relation to each other. They do that with Very-long-baseline interferometry, basically what is the time difference of quasar radio signals hitting their Radio telescopes. The things they account for is wild like local gravity field a couple of super prices atomic clocks etc.
they then laser range find Satellites (all not only gps) which is a „fun“ summer student job at least at the one that I visited.
- This blog post is also worth noting: https://ciechanow.ski/gps/
- Always makes me laugh when you get some dimwit that claims the Earth is flat, but then uses Google maps in his car. Magic!
GPS are amazing. If you understand how they work, and how they reliably know the time etc. you'd think you live in the future; and yet it's everywhere, in our pockets.
by empiricus
3 subcomments
- And then you try to actually build a GPS network, and ask yourself: what kind of antennas should we use? what should be the freq? how much power? how will the receiver detect the precise nanosecond when it receives an incredible weak signal? (in current GPS the signal is bellow thermal noise)
- Pretty cool. Would be nice to have the equation system as well in a recap, and the math not collapsed by default. Also had to look up other resources to understad that time correction refers to correcting a relatively short window of time, as it was not clear that receiver clock is actually accurate enough for short periods (milliseconds) to treat as affine.
So the trick, as always, boils down to engineering approximations, haha.
- if anyone is interested in the gory details of the signal processing side, this is a great resource: http://www.aholme.co.uk/GPS/Main.htm
by sinaatalay
2 subcomments
- Very cool to see these browser-native interactive 3D visualizations! Gives this such a different energy than a regular blog post would have had.
I'm guessing those visualizations wouldn't be in this post if it weren't for AI. The interesting question is what happens when ed-tech ships this pattern at scale. Exciting future.
by NooneAtAll3
1 subcomments
- Page tries to load, then goes:
404
Page not found
Sorry, we couldn’t find the page you’re looking for
- The time part reminded me of the old WWVB radio time signals.
If/when that goes away, I wonder if it will be cheaper to use a gps chip to make "self setting" clocks, or if everything will just be wifi connected.
- For anyone interested in a more detailed account of (general-)relativistic effects in GPS and other positioning systems, I really liked this article: https://pmc.ncbi.nlm.nih.gov/articles/PMC5253894/
by cammasmith
0 subcomment
- Cool article. Did a very good job explaining things simply and providing good diagrams.
- Periodic reminder that you can just buy a cheap IC¹ to rip GPS data signals right out of the air. I built a GPS-powered clock that sits on my desk.
¹ https://www.sparkfun.com/gps-module-gp1818mk-56-channel.html
by ChrisArchitect
0 subcomment
- Previously slightly different url: https://news.ycombinator.com/item?id=47738343
- Triangulation.
Saved you a click.
by openclawclub
1 subcomments
- [flagged]
- What's interesting is the Chinese GPS called BeiDou is way more advanced than the now outdated American GPS system
Except BeiDou is banned on American devices unlike Russian GLONASS
Even though GPS is a read-only service and could not affect civilian devices and it's already built-in to most phone/watch chipsets
Biden admin tried to change policy but ran out of time
https://news.ycombinator.com/item?id=47849174
It will radically increase accuracy and availability the day it's allowed (like in Europe)
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