Things you always wanted to know the answer to [Vol. 5]
Discussion
SCEtoAUX said:
Which is what I was saying, you don't need a data connection for SatNav, all you need is a GPS receiver and something to do the maths.
Didn't sound like it. From your post it sounded like you thought that a phone needed a data connection to do the calculations which it most certainly doesn't. The only difference between a dedicated satnav and a satnav app on a phone is that the former holds all its maps locally in memory and often they don't get updated for years, whereas the phone app generally gets its map data on demand over the internet (although can optionally download it if you don't mind using loads of local storage).Both the phone and the dedicated satnav are doing exactly the same local calculations. The phone does not offload them onto a remote server using a data connection, which is again what you seemed to be saying.
Einion Yrth said:
To be fair, that may well have been what you meant, but your post was not the very epitome of clarity.
That's probably a far more diplomatic way of putting it. 
Edited by Clockwork Cupcake on Monday 24th August 20:06
Rostfritt said:
I can't remember if it was this thread or another, but stand-alone sat-navs can have real time traffic updates that work wherever you have an FM radio signal. I bought one a few years ago and everyone thought I was mad as I could have just used a phone. Except for having to type in an address after I had googled it, I found it much better to use and not dependant on data.
They can get broadcast traffic updates, but they're bulletin-based ones. The beauty of things like Google Maps is that everyone using the app is sharing their speed and position with the hivemind in real time, so that Google can feed that information back out again and do real time analysis of average speeds on a road and detect congestion as it happens, and even re-route other users around it as required. Plus the maps are always up to date.
Ok, the downside is that you are always sharing your speed and position with Google. But that is the price of using the (financially) free app.
Clockwork Cupcake said:
glazbagun said:
GPS is just a bunch of crazily accurate clocks pinging off a signal and allowing a device to triangulate its own position, which is why a wristwatch can do it. You need map software for that position to mean something practical.
Exactly so.Funniest / saddest explanation of GPS navigation I ever heard was when Stephen Fry went Off Piste on QI once and seemed to be under the impression that your GPS somehow asked the satellite to tell you your position, which was laughable. All the satellites do is broadcast their identifier and time, and your receiver does all the clever maths and physics calculations to triangulate your position and then look that up on a map.
Incidentally the calculations always resolve to two positions, but since one of them is in space it can be discarded.
Halmyre said:
Big-Bo-Beep said:
Fastchas said:
I watched 'Se7en' again recently.
As with other films & books, the freak and his gruesome acts of violence is the manifestation of the writer's imagination.
Got me thinking - has any criminal, living or dead, actually done any crimes like the ones you see in movies?
Who would be the closest one to say, Spacey in Se7en or Hannibal in Silence of the Lambs etc.
I'm guessing someone like Fred West or Dahmer but are there worse?
As mentioned Ed Gein was certainly weird and it's stretching it to call him a serial killer, he murdered two women, all the other stuff As with other films & books, the freak and his gruesome acts of violence is the manifestation of the writer's imagination.
Got me thinking - has any criminal, living or dead, actually done any crimes like the ones you see in movies?
Who would be the closest one to say, Spacey in Se7en or Hannibal in Silence of the Lambs etc.
I'm guessing someone like Fred West or Dahmer but are there worse?
was digging up recent corpses.
Certainly it's true that one or two killers taunted the police due to their poor attempts to catch him, Zodiac Killer for one,
but the idea of an intelligent, savant serial killer leaving cryptic messages, deliberate false forensics, ciphers,
and [ most wearisome of all ] killing people in the gruesome manner that characters in greek mythology or
Shakespeare plays were dispatched is pure fictional horse-wash much beloved of book authors and scriptwriters
When my dad discovered audible he went through various police murder mysteries and, again, it's just gore porn. The authors go absolutely mad.
But human beings can be crazy and sadistic - look at what humans do in war zones, the nazi's, the Aztecs, jack the ripper..... It is theorised that most potential "serial" killers get caught at their first murder. But it wouldnt surprise me if there arent a few out there.
SpeckledJim said:
I can see how triangulating from three satellites will give two potential positions. But once there's 4 satellites in range, then it's isolated to one true position, I think?
No, there will always be two possible positions in 3D space. Any solution that gives you a position below the satellites will give you a corresponding position above the satellites too. The only time you will get only one position would be in a 2D plane. It's pretty easy to work out which one you want for terrestrial navigation though.
Trust me on this - I worked on Galileo and this was explained to me, with mathematical proof and diagrams, by satellite engineers who made me feel like a simpleton despite the fact that I have a degree in Applied Physics.
Edited by Clockwork Cupcake on Monday 24th August 21:55
Clockwork Cupcake said:
SpeckledJim said:
I can see how triangulating from three satellites will give two potential positions. But once there's 4 satellites in range, then it's isolated to one true position, I think?
No, there will always be two possible positions in 3D space. Any solution that gives you a position below the satellites will give you a corresponding position above the satellites too. The only time you will get only one position would be in a 2D plane. It's pretty easy to work out which one you want for terrestrial navigation though.
Trust me on this - I worked on Galileo and this was explained to me, with mathematical proof and diagrams, by satellite engineers who made me feel like a simpleton despite the fact that I have a degree in Applied Physics.
glazbagun said:
I think GPS can actually use four signals which would produce a single point.
No. You are thinking in 2D. Consider any number of satellites projecting lines* downwards onto the surface of the Earth to define a single point. Now take those lines, of the same length, and project them upwards instead, and they will converge to a point in space (as in "outside the Earth's atmosphere") as well. So for any number of satellites, they will always resolve to two solutions - one on the Earth's surface and one outside of the Earth's atmosphere. Since we are trying to find a position on the Earth's surface we can obviously ignore that other one.
(* - ok, arcs. But lines corresponding to the radius of the arcs)
Edited by Clockwork Cupcake on Monday 24th August 22:24
SpeckledJim said:
I can see how triangulating from three satellites will give two potential positions. But once there's 4 satellites in range, then it's isolated to one true position, I think?
That would be true. My old Garmin would tell you relatively useless info about the GPS signal. Usually it had about 8 satellites in view if you were out in the open.Rostfritt said:
SpeckledJim said:
I can see how triangulating from three satellites will give two potential positions. But once there's 4 satellites in range, then it's isolated to one true position, I think?
That would be true. My old Garmin would tell you relatively useless info about the GPS signal. Usually it had about 8 satellites in view if you were out in the open.It's because the satellites are way up in orbit looking down on us. So any position below them has a corresponding position above them.
Edit: It's because you draw a sphere around each satellite when doing 3D triangulation, rather than a circle which is what we are used to in 2D triangulation. With 2D the circles will only intersect at one point (or area) but with 3D the spheres can intersect at two points. With satellite positioning that will correspond to a point below the notional plane of the satellites and another above it. And we can ignore the one above it.
Edited by Clockwork Cupcake on Monday 24th August 22:36
Clockwork Cupcake said:
Rostfritt said:
SpeckledJim said:
I can see how triangulating from three satellites will give two potential positions. But once there's 4 satellites in range, then it's isolated to one true position, I think?
That would be true. My old Garmin would tell you relatively useless info about the GPS signal. Usually it had about 8 satellites in view if you were out in the open.It's because the satellites are way up in orbit looking down on us. So any position below them has a corresponding position above them.
Clockwork Cupcake said:
No matter how many satellites you have, there are always two solutions when doing 3D triangulation. We're used to doing triangulation in 2D because that's what we learnt at school.
It's because the satellites are way up in orbit looking down on us. So any position below them has a corresponding position above them.
They can quite comfortably discount the position that is above the satellites though.It's because the satellites are way up in orbit looking down on us. So any position below them has a corresponding position above them.
I still think that would come up with one solution though, as their orbit is in a curve, so as long as you could see 4 of them, there would only be one solution.
MartG said:
That would only be true if the satellites were all located on a flat plane. As they are located in orbit i.e. essentially on a 3D globe in space, the timing of signals from ones not directly overhead ( or below you if you're in space ) will differ depending whether you're above or below the orbit of the satellites
Kind of true. But not always. There will often be a solution that is in space although it may have a greater volume than the one on the surface of the Earth. It's entirely academic for terrestrial navigation though as it is easily ignored. Rostfritt said:
They can quite comfortably discount the position that is above the satellites though.
Yes, I know. And have said so numerous times and indeed have not claimed otherwise at any point.I don't know why we're having such a big debate on this - I only mentioned it as an amusing little anecdote. It's not like the satellites are on a conveyor belt.
Edited by Clockwork Cupcake on Monday 24th August 22:46
MartG said:
Clockwork Cupcake said:
Rostfritt said:
SpeckledJim said:
I can see how triangulating from three satellites will give two potential positions. But once there's 4 satellites in range, then it's isolated to one true position, I think?
That would be true. My old Garmin would tell you relatively useless info about the GPS signal. Usually it had about 8 satellites in view if you were out in the open.It's because the satellites are way up in orbit looking down on us. So any position below them has a corresponding position above them.
Say I'm somewhere in a huge bowl.
If three satellites are anywhere on the surface of the bowl, then the triangulation will tell my sat nav two things - exactly where I am inside the bowl, and (erroneously) exactly where I might be if I was outside the bowl.
If you put a fourth satellite on the surface of the bowl, then the erroneous external-to-bowl result can be definitively ruled-out with the timing reading from the 4th satellite. Because the timing reading for that position wouldn't line-up with the earlier three, because it's not in the same 2D plane as they all are.
Can't it?
SpeckledJim said:
MartG said:
Clockwork Cupcake said:
Rostfritt said:
SpeckledJim said:
I can see how triangulating from three satellites will give two potential positions. But once there's 4 satellites in range, then it's isolated to one true position, I think?
That would be true. My old Garmin would tell you relatively useless info about the GPS signal. Usually it had about 8 satellites in view if you were out in the open.It's because the satellites are way up in orbit looking down on us. So any position below them has a corresponding position above them.
Say I'm somewhere in a huge bowl.
If three satellites are anywhere on the surface of the bowl, then the triangulation will tell my sat nav two things - exactly where I am inside the bowl, and (erroneously) exactly where I might be if I was outside the bowl.
If you put a fourth satellite on the surface of the bowl, then the erroneous external-to-bowl result can be definitively ruled-out with the timing reading from the 4th satellite. Because the timing reading for that position wouldn't line-up with the earlier three, because it's not in the same 2D plane as they all are.
Can't it?
MartG said:
That was my thinking too - unless you're very unlucky and all four are on a flat plane for a brief time, there will only be one location solution. Even more so the more satellites your GPS receiver can 'see'
Well, I'm just relaying what I was told by mathematicians and physicists who were working on an actual satellite navigation system (Galileo) whilst I was contracted to turn their mathematical models into simulation code. It's a completely pointless debate as the 2nd position can be easily discarded. But it apparently does exist.
Ayahuasca said:
Is ‘touch typing’ still a thing?
In the days when only secretaries and typists were required to type, they had to train to do so many words per minute or something and used all their fingers.
Now that everyone types, do we all do it with just two fingers ?
It's not really a thing anymore. In the days when only secretaries and typists were required to type, they had to train to do so many words per minute or something and used all their fingers.
Now that everyone types, do we all do it with just two fingers ?
As you say back in the day Typists and Secretaries were copying hand-written notes or audio recordings into typed letters, or later into computers, they weren't creating anything so speed and accuracy allowed them to do more work more quickly.
These days most people do their own data entry so even 2-finger keyboard bangers can usually type quick enough to keep up with their thoughts. Most people actually type with 5 fingers now, the 90% of the time they're using their two index fingers with the occasional trip over to QW OP AS or KL with their middle fingers and the space bar with one of their thumbs.
I've got a Guy on our Helpdesk (IT Support) who uses all of his fingers, he's a pianist when he's not working here, he's quick, just he can't spell for s
t and his accuracy is appalling...Some do exist though, the Royal Mail uses a small army of Data Entry clerks who fill in the bits that the sorting machines can't read, the money is poor, it's basically minimum wage to sit in front a of screen all day as thousands of scribbled post codes are shown to you to enter. I think they want 60wpm and 95% accuracy. I hear they like to use a lot of agency staff because the numbers of people of with stress, RSI is really high.
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