Satellite Navigation: HOW does it Work? | Earth Science
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- Опубликовано: 15 дек 2024
- Sat Nav has revolutionised navigation, bringing military grade satellite positioning to the consumer. But how does it work? James May steers us through the science of Sat Navs in this Headsqueeze video. Subscribe for more fascinating science videos: bit.ly/Subscrib...
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James May's Q&A
With his own unique spin, James May asks and answers the oddball questions we've all wondered about from 'What Exactly Is One Second?' to 'Is Invisibility Possible?'
Welcome to BBC Earth Science! Here we answer all your curious questions about science in the world around you. If there’s a question you have that we haven’t yet answered let us know in the comments on any of our videos and it could be answered by one of our Earth Science experts.
Friday is a horrible day at school, boring classes... But when I get home I find a new James May's Q&A and that makes the day :P
In fact, there are now some chips that can receive signals from four networks (GPS, Galileo, GLONASS and Compass / Beidou).
Jeremy : Where's May?
May : Backing it upon the sat nav!
I love James May! What a practical man!
the GPS James is in is seriously broken.
Hence James's famous sense of direction
mrzkhan1 or lack of...
somethings wrong with the satellite
NetMoverSitan thereof*
Tommy59375 He goes in the right direction usually if aided by sat nav (that doesn't involve him making it)
It's Special Relativity that tells us that time slows for moving objects. General Relativity tells us that time slows in a gravitational field. This makes the satellite clocks speed up. The effect of General Relativity is more than Special Relativity in this case.
You actually need to have 2 satellites to get the distance only. One to calibrate time and one to get the distance from. With three you can get a ring position and with four satellites you can get a point position... actually you get two point, but one is far out in space so the GPS just ignores it.
The accelormeters, compass helps with angles and headings, but not with precision. The phone mast system is less accurate than the GPS system.
What you probably confuse it with is A-GPS, Assisted GPS that use ground based repeater system that re-calibrate the error in the GPS system, giving it about 10 or so times better accuracy.,
It's good to watch James may when you having a hard time trying to sleep. After 3 minuets I was a sleep on my chair.
I assume you mean "if you let go of the top end after you have allowed it to stretch to its full equilibrium length".
And that's because, at its maximum "natural" (equilibrium) length, the tension on the spring matches the pull of gravity. So, when you let go, the spring pulls its bottom "up" at the same rate as gravity pulls the whole spring down, so the bottom appears to be stationary.
If you drop it while it's compressed (or over-extended), the bottom definitely moves.
They can disable or greatly reduce the accuracy of unencrypted (i.e., "civilian") signals on individual satellites (effectively making GPS unavailable in some areas of the globe).
They can also jam the signal on the ground, but the point of controlling the satellites is they don't need to do that.
Brian freeze is when you eat something cold quickly (that touches the top of your mouth) and your blood vessels quickly contract and swell causing pain signals that get confused (theoretically, I believe) as your brain thinks the pain sources from different parts of the head, I believe this is to do with the top of your mouth being so close to the brain. Idk if this helped or if you just wanted a video on it but yeah, this is all I know c:
Navigation software does a few tricks to "extract" higher precision than the signal actually carries. If it determines that you are probably standing still, it starts to average several samples, and progressively refines your position. And if it determines that you're moving along a road, it "snaps" your location to the road, even if the signal fluctuates a bit.
But if you want real-time tracking with full accuracy, you need a military GPS receiver (or Galileo).
I like how you were displayed on your own sat nav, talking about sat nav's, while doing 90kph through a city centre and obviously going nowhere in perticular.
True. What I'm saying is that once the signal is received, it must be processed by CPU (or other means). And processing of the GPS signal takes more battery than a LCD. This is my experience so far, the subject did start to interest me more now so I will make some measurement to be sure.
Can you explain why we hate to listen to our own voice ?
When we speak, we hear extra resonance because of the air column we are using. Every airspace has resonant frequencies. This is what you hear when blowing across the opening of a partially empty bottle. Even the skull vibrates, and the eardrums receive some of this extra resonance. The resonance is like reverberation (reverb), and makes our voices sound richer, but only to ourselves. Outside listeners (or recorders) detect only the sound waves that have left your mouth. This is why everyone thinks that recordings of their own voice sound strange, but others don't agree.
It's okay to be smart covered it in one of their videos.
what application do you use for all the animation in your vids? im very impressed.
I think it's neat that some GPSs have a feature that can guess where you are if you go in to a tunnel or some place that has no GPS connection. It remembers what road you were on and about how fast you were going in general and then keeps guessing where you'll be on that road while it has no signal.
It's also QI that it's called Dead Reckoning.
There is effectively still a difference in accuracy between civilian and military GPS. While the original "SA" was disabled (and not even included in newer satellites), the high-accuracy part of the time codes is still encrypted, and civilian receivers can't read it (hence the accuracy of around 10-15m, while military receivers are accurate to about 1-2m).
Galileo, on the other hand, has 1m accuracy for everyone (free), and 1cm accuracy for commercial use (airlines, etc.).
Hmm, I stand corrected for the GPS and GLONNAS support on modern devices. It does still need 2 hardware receivers (since GPS uses CDMA modulation and GLONNAS uses RF channels). I do stand by the fact that only GPS and GLONNAS systems have 'global' coverage, others do not yet. I doubt that it uses both at the same time (kills the battery).As stated in lea*hamradio*si/~s53mv/navsats/software*html using GLONNAS and GPS together gives you accuracy 10m on average. Everything else we agree on I think.
It is pulled up by the tension in the spring, and pulled down by gravity. As long as there is tension in the spring, the bottom stays at equilibrium. Newton in full sprint. Action=reaction
It would, and that's why they don't do it (because it would affect airlines, etc.).
Well, actually there's more to it. The US military wanted to keep that option, but the EU threatened to make Galileo satellites operate on the same frequency range as GPS, which would make it impossible for the US to jam Galileo without jamming GPS, so eventually the US agreed to disable the "Service Availability" option, and now they just make civilian GPS a bit less accurate near war zones (or jam it locally).
Yeah, so from 2:00 to 2:09, he needs to tell me what site he was on, cos apparently they've got content that will make you do it until you start generating smoke. I think the illustrator knew exactly what he was doing when he put that animation together.
Can't say I find the background dizzying but I guess that's just me. Informative vid as always :P
at some point i switched to read the comments rather than watching the video because the background is so iritating - still james voice is awesome
Great video James. Thumbs up from Shreveport La. I got my while family watching you guys on top gear.
Great video, I've always wanted to know how Sat Navs work :). Thanks.
No link to enterprise video in description :-(
great explanation of gps from captain sense of direction.
BTW, most multi-format receivers use single-chip solutions. Naturally, internally, some parts are only used for some constellations, but most of the logic / power regulation / clock / etc. circuitry is shared, so it doesn't add to power consumption.
GLONASS is a global positioning system, just like NavStar, Compass or Galileo. Lots of SatNav systems use signals from multiple satellite networks.
I have no idea why but when the soldiers that are completely fake I jumped and my heart pounded for a minute
I didn't say anything about the relative power consumption of a CPU versus a screen. I was talking about the increase in total battery consumption from adding a second satellite receiver.
Power used by the CPU to process the signals will depend mainly on the number of satellites it's using (which can be limited in software). Processing 4 GPS signals + 4 GLONASS signals uses about the same CPU as processing 8 GPS signals (but does require a second receiver, which was the issue).
How does a fridge work? With that in mind, why does the 2nd law of thermodynamics state that if you try to cool a room using a fridge, the room will actually get warmer (or is that assumption/statement wrong)?
Awesome video!
I have a question related to evolution: what do we mean by "the first human/homo sapien", in scientific terms? In other words, when and how does a new species just appear?
thank you humanity for the Waze :)
He didn't mention why you need four satellites. But it's actually because the need to solve for time. You have four unknowns (latitude, longitude, height and time) so you need four knowns (ranges to four satellites). If you know your height it is possible to do it with only three satellites.
How I love you, James.
It is impossible to reach the Head Squeeze HQ.
Your a legend James ;)
you're*
I wrote that comment almost 2 years ago.
+Charlie Clumsy congratulations
iamhim Thanks!
Captain Sense of Direction
I loved the background!
When my satnav boots it reads the time from the satellites... and uses it to set a cheap quartz clock that it uses for all subsequent time displays, even though it has to continue to calculate accurate time in order to determine its location.
Every iPhone model released after the 4S (inclusive) supports both GLONASS and GPS. Same for recent Lumias, Galaxies, etc.
Some receivers even support 3 or more systems. If your receiver supports multiple standards, you get faster and more accurate fixes in any regions covered by them.
Also, BeiDou does not have "only 3 satellites", unless you've been shooting them down in your spare time. It had 10 in 2011, and probably has a few more by now. It covers most of Asia, and is expanding.
OFC it would help you much better than a person from 50 years ago! Do you know how many kinds of roadwork and re-building has happened since the 60's? ^^
"Look like a knob"🤣🤣i love james
I think it`s worth mentioning that the orbiting satellites have slightly slower atomic clocks to counter the effects of special relativity because of the degraded gravitational pull from the Earth, i`m surprised you didn`t put that in.
Quick question - do the NAVSTAR satellites have a theoretical limited bandwidth - i.e. a maximum number of users at any time? It's clearly a very clever system and I love my sat nav!
If you still don't know that and looking for answer - the answer is no, because satellites are only sending their signals but aren't receiving anything from users so they can't even know if there are any users at all. Imagine you walking on infinite pathway through forest and constantly yelling only what time is it now. And wearing sound suppressing headphones. And blindfold. And you have no chances to meet anyone, talk to them... There are someone somewhere listening to you yelling. Probably... But they can't reply to you because they're so tiny and even if they had mouthes, you couldn't hear them at all. That's how nav satellites are. They're so lonely...
I believe GPS receiver manufacturers pay a fee (the technology is patented), and that cost is passed on to consumers when they buy the device. Same goes (for example) for some video compression codecs (everyone gets to play the videos for free, but encoders and broadcasters pay a fee to the patent holders).
And other countries have put up navigation satellite networks too, although this video seems to ignore them completely. GLONASS, Compass, IRNSS and Galileo, for example.
That's a bit like asking if a radio station has a limited number of listeners, or if a light bulb has a limit on how many people can see it.
I was once going down a road (forget where) and my sat nav said there was a round about a few hundred yards down the road. I got to where it said the round-a-bout was, it was the end of the road and you could only go left or right and I don't think there was ever a round-a-bout there.
Modern GPS receivers are also compatible with Galileo satellites (operated by the EU, with higher precision than GPS, and not under military control).
As expected of James May! :D
I expected James May to at least mention relativity... That's the real head squeeze of GPS.
Awesome!
Can you explain imperial measurements and metric measurements
A basic GPS dey vice cannot be tracked in the way you're thinking. Notice that the description of how it works was all about your GPS RECEIVING signals from the satellites. It doesn't TRANSMIT anything. So your GPS knows where the satellites are, but not the other way around. It's not like a transmitter capable of sending a signal to those satellites could fit in your satnav unit. A smartphone is trackable, because it's connected to the cell network and can transmit your position that way.
If the Earth was flat (or a perfect sphere) and everyone was on its surface, yes, three would be enough. But if you want an altitude reading, and if you want it to work at any latitude, you need four.
Strangely enough, this cropped up on a QI episode I watched the other day :D
That's not a feature of GPS itself, it's a feature of the SatNav software. GPS is the satellite network, it doesn't have any road / navigation logic built in.
... 'bout time the greenscreen was utilized ... loved this vid and the info was superb .. well done squeezers √√
James understands how satnav works but he still gets lost xD
That's fascinating.
Damn that was a long .2 miles to the Headsqueeze HQ
We got fax machines from the government too. Slightly less relevant than they were 20 years ago, but it's pretty interesting how many bits of technology we take for granted came from government research. Also, much more notably, the internet.
Theres a reason so much technology comes from Darpa and Silicon Valley like Lifelog or Facebook after name change, it will end up controlling your life though
Contact with one satellite gives you NO information on where you are. Contact with two satellites gives you the ability to narrow down where you are to a hyperboloid (not a sphere). Contact with three satelites gives you a curve, and four satellites give you a single point (up to some accuracy) There are NO spheres or radii involved in calculating where you are. Of course, once you know where you are, you can use spheres and radii to figure out the time based on the satellite pulses.
There was something nice about taking in your surroundings and getting your bearings though.
Your Right, You had to use Braincells back in older days, no one needs that now, just Big Pharma Jabs and Black Mirror Device (smartphone)
2:05 the computer wasnt there before. right? :D
Wow I saw that I tapped back to see, landed right on 2:05
I'm surprised there's no mention of the dual GPS/GLONASS sensors in newer phones!
The Short answer: MAGIC!
Can you explain me about time travel isn't possible to do time tarvel
Listen to Michael Feeley, he explains it
James May!
Everything "takes battery", but there's absolutely no comparison between the battery use of a GPS receiver and the amount of power used by the CPU, graphics chip and the screen itself, while running any remotely complex application (such as SatNav software, which keeps the screen on all the time and is constantly redrawing the image, often in 3D).
James Sir, could you fly an aeroplane underwater? Ignoring the fact that everything will get soggy and the pilot might drown, would the aerodynamics work?
im not sure how i feel about taking navigation tips from james may
Says Captain Sense of Direction
Actually the absolute minimum is 4, not for a 'reasonable' result but plain simply for a result. Unless the GPS device also uses its altitude map to know where you are.
Without altitude map 1 satellite gives you a sphere of possible locations, 2 give you a circular plane where the 2 spheres intersect. 3 give you a line on that plane, 4 give you a point. More satellites will obviously give you a more accurate result.
What's with May's audio reacording?
im dissapointed
he didnt mention the Romanian translator
Shit
Device size won't be an issue for much longer with new HUD systems in helmets and windshields..
HAHAHA The Typing guys hand :P
My Garmin e-trex 30 says, it navigates via GPS & GLONASS - and the accuracy is down to but 3 meters.
that gps background that is behind james may gave me a headache from all the spinning that it does
they need to remake this
Thanks, i try.
You mean gravity's effect on the passage of time?
As in time in space moves at a different rate then time on earth?
Pure ASMR
I agree with the top comments.
I remember hearing that sat-nav satellites were in Geosynchronous orbit. What happened to that?
You didn't even touch on GPS Survey techniques. Our GPS System has sub centimeter accuracy.
The sat nav display was nice for 10 seconds. Then it stopped being nice.
Why was the gentleman attacking his bell @2:00?
Kenmore navigation Dynamax system
This video needs to be re-titled. As James says at the beginning, he explains (very well) how a Sat Nav works out where you are, but he doesn't explain how it calculates the best way to get where you're going. He actually says this at 4:30, but then leaves us hanging...
All that technology, and it still takes you through 12 countries if you tell it it can't take the A44 (or whichever road it was on that one episode of Top Gear).
Unless, of course, it was Clarkson, in which case he'd probably just mute you and end up lost anyway.
Surprised you didn't mention that the satellites need to account for time dilation - what with being slightly further out of Earth's gravity than your car. All the clocks on all the satellites can be incredibly accurate, but that's useless if time is passing faster for them than it is on the ground.
I do disagree with you in this. Not the receiver part, but the amount of CPU (or DSP) that it uses to demodulate (if software defined radio) and then make the calculations takes battery.
Top Gear Liked :D
Captain Sense of Direction
- Jeremy Clarkson Race across Japan Episode
You're welcome.