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GPS

ciechanow.ski

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Re: GPS

#121

Post by daenz »

Unklejoe wrote: post #114
alesua93 wrote: post #112

Earlier quoted context omitted.

> General curiosity and interest in areas outside their field of specialty. This might not be strictly necessary to get a job done, but it probably has some correlation with other measures of technical aptitude that are hard to probe directly. I think this is a bit misguided, since the scope of things outside of a candidate's field of specialty is tremendously large. Picking a random piece of tech within that space a…

> random piece of tech IDK. GPS is probably one of the most prevalent technologies used today besides the Internet itself.

Chip manufacturing is even more prevalent. Why not ask a candidate about how silicon wafers are made?

Re: GPS

#122

Post by Unklejoe »

alesua93 wrote: post #120
Unklejoe wrote: post #114

Earlier quoted context omitted.

> random piece of tech IDK. GPS is probably one of the most prevalent technologies used today besides the Internet itself.

Fair enough. I understand where you're coming from, at the end of the day I guess it depends on the context and the way the question is presented (left-field questions such as this one can be somewhat fun to try to answer and hypothesize about, if the interviewer creates a friendly environment to do so)

I hear ya. I would definitely not disqualify someone for not knowing the answer.

In fact, someone who is able to sort of work through the problem on the spot may even be preferable to someone who just knows the answer because they happened to read Wikipedia the week before.

Re: GPS

#123

Post by Youden »

daenz wrote: post #81
gsibble wrote: 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.

This is going to come across as harsh, but if that is your favorite interviewing question, and you are not hiring GPS engineers, then it is a ridiculous question to ask and serves no purpose but to "haze" candidates.

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__, come to a basic understanding of how GPS works and come up with a reasonable (note: not necessarily correct) suggestion for how to implement it?

Re: GPS

#124

Post by daenz »

Youden wrote: post #123
daenz wrote: post #81

Earlier quoted context omitted.

This is going to come across as harsh, but if that is your favorite interviewing question, and you are not hiring GPS engineers, then it is a ridiculous question to ask and serves no purpose but to "haze" candidates.

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.

Re: GPS

#125

Post by JackMcMack »

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? From ground stations, sure, but how exactly? What's the margin of error on that?

And to add to this, how do you bootstrap this?

Galileo had an outage from 2019-07-11 to 2019-07-18 [0]. I've not read much about the details what caused the outage, or why it took an entire week to get back up & running.

[0] https://www.gsc-europa.eu/news/galileo-initial-services-have...

Re: GPS

#126

Post by avianlyric »

daenz wrote: post #108
mellavora wrote: post #101

Earlier quoted context omitted.

You've received some flack for this, but I'm not sure the context. If most of the questions in this round are of this nature, then maybe it is a "why are manhole covers round" thing. But as a one-off, and if asked in a forgiving way to explore how they think, then I'd consider this question valid. Maybe "Have you ever thought about how GPS works?" if "yes", then let them explain, if "no", then make it easy for them t…

I don't understand why you think linked lists and db replication, which I think are both are very appropriate questions for a software engineer (less relevant to FE engs), are as relevant as how GPS works.

Depends on what you’re evaluating the candidate on. If you’re evaluating the candidates ability to reason through a problem, and communicate the reasoning, the. GPS is arguably a better question for a software engineer as they’re unlikely to have studied it. Thus you can watch them work through a problem they haven’t thought about before, but which should probably have the basic tools to solve.

There should be no expectation of them coming up with the “correct” answer. But they should be able come with an answer and explain it clearly, warts, holes and all.

Using something real like GPS also ensures that the candidate understands why the problem is a useful problem to solve, and what the objective of the solution is I.e. a system that lets you locate yourself on earth.

Re: GPS

#127

Post by lazide »

daenz wrote: post #108
mellavora wrote: post #101

Earlier quoted context omitted.

You've received some flack for this, but I'm not sure the context. If most of the questions in this round are of this nature, then maybe it is a "why are manhole covers round" thing. But as a one-off, and if asked in a forgiving way to explore how they think, then I'd consider this question valid. Maybe "Have you ever thought about how GPS works?" if "yes", then let them explain, if "no", then make it easy for them t…

I don't understand why you think linked lists and db replication, which I think are both are very appropriate questions for a software engineer (less relevant to FE engs), are as relevant as how GPS works.

Only reason I can think of is it is a real world example of distributed coherency/information problem and if you squint hard could give insights into things like paxos (and why it does what it does), why certain types of keying/sharding/distributed computing are done the way they are done.

But directly talking about those topics is probably handy.

Re: GPS

#128

Post by lazide »

daenz wrote: post #104
Mindless2112 wrote: post #95

Earlier quoted context omitted.

You either find out the candidate knows how GPS works or you find out the candidate's willingness to say "I don't know". It's valuable to know how someone will handle a question they don't know the answer to -- whether they recognize their own ignorance and whether they are willing to admit to it.

There are plenty of ways to get to the bottom of what a candidate knows without resorting to unreasonable questions. What you're really testing for is a candidate's patience for being toyed with.

Or the candidates ability/willingness to bullshit in order to not look ignorant or unskilled in something.

Which is actually useful to know, even if this method would be a dickish way to do it.

Re: GPS

#129

Post by avianlyric »

daenz wrote: post #121
Unklejoe wrote: post #114

Earlier quoted context omitted.

> random piece of tech IDK. GPS is probably one of the most prevalent technologies used today besides the Internet itself.

Chip manufacturing is even more prevalent. Why not ask a candidate about how silicon wafers are made?

Because that’s not a problem you can solve with software and algorithms. That a chemical and lithographic problem that requires a knowledge that rarely overlaps with software.

However GPS can be solved with some high school maths, and applying solutions found on the software engineering domain E.g. computing distance from latency, communicating with a remote resource over a comms link, broadcast vs unicast etc

It’s not like the interviewer is going to ask them to design the satellites and rockets themselves.

Re: GPS

#130

Post by lazide »

wonnage wrote: post #119
littlecranky67 wrote: post #100

Earlier quoted context omitted.

Actually this is a very good question for engineers , as the (wrong) idea that a smartphone regularly sends data to a satellite shows fundamental lack of knowledge in some very basic physical understanding. The basic understanding should be: transmitting/sending = emitting energy (costly if a device runs on batteries), receiving/listening for a signal = almost for free nowadays. I also like the question because even…

I have a hard time imagining engineers in any other field (e.g a structural engineer) would be getting asked questions about GPS as a proxy for general engineering knowhow.

Do you have experience interviewing or seeing interview questions in those fields?
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