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GPS

ciechanow.ski

71–80 of 296 posts

Re: GPS

#71
post #11

This person deserves to get filthy rich off of their patreon.

Thought I'd link Patreon, here: https://www.patreon.com/ciechanowski

Thanks, I created a Patreon account just to support him :-)

For anyone who is still hesitant: Just do it, it feels so good to put your money where you mouth is ;-)

Re: GPS

#72
post #41

This is very nice. Very clear, and the 3D interactives are excellent at guiding the explanation. One thing that I thought was a little confusing was right at the beginning, when we were estimating the position of the figurine and there was an area of uncertainty shown by the yellow circle. It isn't clear how you're estimating position, and why we have an area of uncertainty. At first I figured it was going to explain…

Yes, that section is poorly written.

More generally, the assumptions about what things were uncertain and what could be taken as exact were poorly motivated. The author should wither justify them with real-world constraints ("satellites can host atomic clocks but destroyers can't" -- not obvious!) or explicitly announce the assumptions as unjustified, but he shouldn't make it seem like the assumptions could have been reasoned to by the reader.

I also was disappointed the author used circles/spheres and guesses for the timing offset rather than the much more edifying choice of hyperbolas. Just as you can think of a sphere as points reachable by the end of a rope of fixed length tied to a post, you can think about a hyperbola as the points reachable by tying separate ropes to two posts and spooling out equal amounts of rope.

Re: GPS

#73

Considering GPS was originally created for military purposes, I find it fascinating that the largest holes are over the north and south poles. The northern polar region is where the US-launched missiles and bombers would travel. Does the lesser orbital coverage in that area not negatively affect GPS precision?

[deleted]

Re: GPS

#74

However, I do like the role GPS plays as a plot device in all kind of stories, where it's an active device, with GPS-enabled devices giving away position or there's no GPS in the wilderness, as mobile connections fail. So there are two versions of GPS, the popular plot device and the actual navigation device. (The more sinister version is that this has actually been planted as a cover-up for more realistic electronic…

The original study by Woodford and Nakamura (which laid the foundations for what eventually became NAVSTAR/GPS) has a really fascinating slide where they consider the tradeoffs of alternative configurations. What if GPS receivers had transmitters? What if the mathy computation was offloaded to a nearby ground station? What if every GPS receiver had an atomic clock? Or just a cheap quartz clock? How does that impact the quality of the signal and the number of satellites you need to get a fix?

I think we're really fortunate that they made the choices they did. If they hadn't take the route that was the most complicated technically, GPS wouldn't have become as ubiquitous as it is today.

Re: GPS

#75
One of my favorite engineering tech interview questions is asking an engineer how they think GPS works. You won't believe how many people start with: "Well, your cell phone sends a signal to the satellite......."

Amazing that even engineers don't understand that GPS receivers don't talk to the satellites.

Re: GPS

#76
post #75

One of my favorite engineering tech interview questions is asking an engineer how they think GPS works. You won't believe how many people start with: "Well, your cell phone sends a signal to the satellite......." Amazing that even engineers don't understand that GPS receivers don't talk to the satellites.

I don't quite understand how such questions help in the hiring process? It reminds me of the famous "why are pothole covers round" question, still not sure what it achieves.

Re: GPS

#77
post #75

One of my favorite engineering tech interview questions is asking an engineer how they think GPS works. You won't believe how many people start with: "Well, your cell phone sends a signal to the satellite......." Amazing that even engineers don't understand that GPS receivers don't talk to the satellites.

Unless you're hiring them to work in that domain, I don't understand why you'd ask that question.

Re: GPS

#78
post #48

If you have not yet seen the other articles by Bartosz, I am jealous :-) https://ciechanow.ski/archives/

Why are you jealous of someone not reading the other articles? Are they factually incorrect? I found them to be amazingly accurate.

sorry for not being clear. Yes I referred to the joy of discovering them for the first time.

Re: GPS

#79
As someone who learned about GPS and was impressed by its structure, I used to tell my friends around me, whenever I had the opportunity, how great GPS was.

Now I saw this article and I got goosebumps, well done, thank you very much! It's really fantastic. From today it will be enough for me to just share this article with my friends, or I will tell along with this article.

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