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GPS

ciechanow.ski

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Re: GPS

#161

Post by FabHK »

masswerk wrote: post #25

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…

Related:

When I fly, I like to cache a map of the region I fly over on my phone, particularly the airport region at the destination. Then, you can hold your phone to the window for a few minutes and get a GPS fix, even if in airplane mode, because as you say GPS is purely passive.

Then you can follow along nicely where you are, at the resolution you want. (Sure, many airlines have moving maps, but they're not as good as Apple maps or Google maps.)

Re: GPS

#162

Post by tiborsaas »

juxtaposicion wrote: post #16

How are these interactive visualizations made? As a senior machine learning engineer (with only rudimentary JS skills) it would be fantastically fun to make something like these.

The author wrote his own WebGL library. If you don't have much knowledge about 3D, then https://threejs.org/ is a fantastic library to learn. It abstracts away much of the tedious part.

Not sure what's the best starting point to learn, but there's lots of videos on YT to help you get started.

Re: GPS

#163

Post by Youden »

daenz wrote: post #124
Youden wrote: post #123

Earlier quoted context omitted.

I think you're unfairly assuming something about how the question was used. If the intent was to find out if people __knew__ how GPS worked when they didn't need it for the position, sure. However I see two other possibilities: - How does a candidate react when they don't know something? Do they try to bullshit their way through? Do they admit it and ask what you'd like them to do? - Can a candidate, __with guidance_…

I agree with the meta interview concept, but I don't think that applies here because of the OP's last sentence: >Amazing that even engineers don't understand that GPS receivers don't talk to the satellites. They're amazed at the lack of knowledge, not that a candidate wasn't able to talk it out, or that they bs-ed through it. That tells me the question is asked in bad faith.

Again, that's not necessarily how that's intended. The observation on its own is just an observation, it doesn't indicate anything about how interview performance was evaluated.

For example when I interview, I have a question related to chess, which requires a basic understanding of how the pieces move. I was amazed that even engineers don't understand the basic movement rules of chess.

However as far as the interview went, it was a non-issue. It took about 30 seconds to explain, not a single candidate had a problem with it, and it never came up when I was giving my verdict.

Re: GPS

#164

Post by SomewhatLikely »

From the toy model it seems like if in addition to distance you could also get your angle to the landmark then you could get your position from a single landmark. Is that something which is practical? Knowing which angle a radio signal came from? It seems like if you had several receivers you could use the timings of when they receive a message to determine the approximate direction of the satellite in the sky. Given receivers have gotten much cheaper over time, is this a viable extra constraint to improve accuracy?

Re: GPS

#165

Post by scrumbledober »

SomewhatLikely wrote: post #164

From the toy model it seems like if in addition to distance you could also get your angle to the landmark then you could get your position from a single landmark. Is that something which is practical? Knowing which angle a radio signal came from? It seems like if you had several receivers you could use the timings of when they receive a message to determine the approximate direction of the satellite in the sky. Given…

then you're basically just doing the triangulation backwards. I'd think the accuracy would decrease the closer together your multiple receivers were

Re: GPS

#168

Post by mpmpmpmp »

seanalltogether wrote: post #118

How feasible is it to speed up the bitrate used by GPS? This really helped explain why it takes so long to get a position based on how slowly these satellites are sending information.

I think the slowness of the bitrate is about making sure any errors in transmission caused my the atmosphere can be detected and accounted for.

Re: GPS

#169

Post by structural »

JackMcMack wrote: post #125
eminence32 wrote: post #6

There's a lot of really great info in here. One random things I learned from this: > As that angle increases, the signal from a satellite travels more sideways and its larger portion gets affected by the atmosphere. To account for this, GPS receivers ignore ranges measured from satellites at very low elevation angles. ... atmospheric effects are primary source of GPS inaccuracies. (I know GPS has inaccuracies, but I…

Something not mentioned: the "new" L5 signal at 1176Mhz, combined with the existing L1 signal at 1575Mhz, allows the receiver to estimate the atmospheric effects and reduce the uncertainty, allowing for a much better position fix. Think centimeters instead of meters. One more thing I've wondered: the system depends on the sattelites knowing and broadcasting their exact position, but how do you determine this position…

The knowledge of a satellite's orbit is taken by using the prior parameters of the orbit, predicting where the satellite will be, and pointing a combination of telescopes (for precise angular measurements) and radars (for precise distance measurements) at this location, and measuring the error between where the satellite is and where it is expected to be. A set of these observations are then used to update the "known" orbit.

This known orbit is then provided back to the satellite so that it can be broadcast. If this system of updates stopped working, the quality of GPS position estimates would degrade pretty quickly (think weeks, not years).

This also means that if a GPS satellite were to need to maneuver for some reason -- either periodically boosting back into its assigned orbit or for debris avoidance -- the normal system of updates will catch this and users will never have to know or care that the satellite moved.

Re: GPS

#170

Post by pahn »

juxtaposicion wrote: post #16

How are these interactive visualizations made? As a senior machine learning engineer (with only rudimentary JS skills) it would be fantastically fun to make something like these.

not what he/she uses, but if you are interested in these kind of things, check out https://cables.gl/ .

it provides you with an in-browser, graphical, node based interface where you can just connect boxes together and it will output js-code ready to implement in your website.

(disclosure: i know the dev plus am a huge fan!)

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