How does GPS work?
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- čas přidán 16. 08. 2018
- This video explores the technicalities of how Marine GPS units can calculate position wherever you are in the world.
In this video, GPS means the system developed by the USA called NAVSTAR GPS. Other Global Satellite Navigation Systems are available.
Read the article that this video is based on here: casualnavigation.com/marine-gps
GPS is used by merchant ships, navy ships and pleasure boats as a way on finding position at sea. As a navigator, it is important that you know how GPS actually calculates position so that you know when it is feeding you false information.
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The video provides a good simple illustrations and a good description of how GPS works. The narration of the video is really high quality. The accompanying article, "How Does Marine GPS Work?", mentioned in the video (link provided) provides a concise document that corresponds to what is covered in the video. Casual Navigation also provides another article, which is a great tutorial on navigation, "What is a nautical mile and why is it used?". Look for the link at the end of the article mentioned above. In my opinion, all three are well worth the investment in time.
FYI: if you see a clock running FASTER than your own, that's not due to speed. Special relativity is symmetrical, as motion is relative, every observer thinks they are standing still. So every observer sees other objects' clocks running at the same speed (when stationary relative to them) or slower (when moving in some direction). The faster clocks come from being farther up from the gravity well, which is general relativity.
The relativistic time dilation is not only due to the speed (you've got that backwards), but also from the gravitational potential (it is farther away from the earth, with less influence from Earth's gravity). Search about *gravitational time dilation*.
Literally, you head is literally getting older faster than your feet.
The speed actually would make the clock to slow down (the faster you travel, the slower the time passes, compared to the rest), but the gravitational potential wins (the farther you are from the source of gravity, the faster it goes), so the net effect is that the time in the satellite goes faster than the Earth.
I stumbled on to your videos and found them extremely interesting. I subscribed to your channel and look forward to seeing all your videos. You do a great job at explaining things visually and verbally! Keep up the great job you're doing.
As a gps software engineer, this is very good. It may be beyond explaining how but r.t.k. gps receivers can achieve accuracies less than a quarter inch. Making them useful for survey applications..
I just read the Wikipedia page thanks to your comment. Cool stuff. Any idea how feasible it would be to have base stations on cell towers and have them act as CORS nodes? We'll need something like that for autonomous vehicles to become practical. LIDAR is well and good, but knowing the position of the vehicle relative to the road with 1-2 cm accuracy in snow and rain will be crucial.
@@phizc the biggest problem is economics, rtk receiver are very expensive. But other than that weather will degrade performance. In other words difficult but not impossible.
I have searched every video on CZcams for GPS but this one is best excellent explanation good voice and animation very easy to understand keep it up bro
Excellent video! I would include: With only 1 satellite the position will be within the surface of a sphere. With a second satellite, the position will be within the intersection of 2 spheres; that is, a circle. With the 3rd satellite the position will be within the intersection of the circle and the sphere; that is, 2 points. With the fourth satellite you will have a unique possible position. More satellites will increase accuracy.
This is the best explanation of gps technology.
Thanks Bruno. Glad the explanation worked out
Was just going to write this, the other videos I watched felt like the "explainers" had no idea what they were talking about and were just reading Wikipedia page.
No it's not. GPS does not run on satellites. It runs on high altitude balloons.
@@CasualNavigation Not both?
@@ZackWolfMusic dont forget your tinfoil hat, lmao
Not reall was looking for anything just got interested in one of your videos and now I’m stuck here listening to explanations of boats and signals
The best part is that is casual and the edits are simple
7:34 This is slightly wrong. *Special* Relativity says that the satellite clocks run SLOWER due to relative speed.
However, *General* Relativity says that the satellite clocks run FASTER because they experience less of Earth's gravity. The gravity effect is far greater than the speed effect, and so the satellites have a net gain in clock speed.
blah blah blah blah just shut up
@@vishnu9264 They’re just giving legitimate criticism.
It’s true - both special and general relativistic effects need to be taken into account. Failing to do so introduces range errors on the order of tens of meters(!) on the face of the earth - surprisingly significant for something most of us rarely think about in our daily lives.
Thank you! I was about to comment the same thing.
Not slightly wrong, gravely wrong. A mess.
The best GPS video. Summarizes many topics under the GPS quite brilliantly.
Thanks Maneeb
The relativistic error comes mainly from the theory of General Relativity, the sattelites are further out of the gravity well that is the earth and therefore their clocks run faster compared to our clocks on (or near) the surface.
both effects take place and must be accuunted for
actually TobyAsE120 is right, (the video explains it wrong, from our frame of reference a fast moving object should experience a slowing of time, but) since that speed is really not that great compared to the speed of light, the gravitational effect on time is much greater here and so it actually IS the main reason satelites' clocks run faster.
@@supawooky And technically the guy above you is right.
Such a good explanation man.
Thanks a lot. It was very helpful.👍
Congratulations on 10k subscribers! YT just recommended one of your videos and you had exactly 9999 subscibers so I thought might as well be your 10000th subscriber :)
Thanks Mario. 10k is unbelievable to me already. Huge thanks to everyone who has enjoyed the content enough to subscribe.
@@CasualNavigation 2 years later, 23 times more subscribers. You deserve it man!
very helpful , and the explanation was very clear.
Very clear and not too complicated. Great
Since you're a pilot, it would be interesting to know if you use any special GPS equipment. I watched a video on piloting in the Houston Ship Channel, and the pilot brought on his own high quality GPS system and attached it to the ship. Then it was related to the position on the ship and the specific dimensions of the ship, so they had a very accurate representation of the exact position of the ship in the channel. They've got really tight space restrictions in the most inshore end of the channel. It's also one of the relatively rare navigable non military places that no unauthorized boats or ships are allowed in the US. The combination of the narrow confines and the strategic significance of all those oil processing and loading facilities mean that there's a big sign, as well as protective measures to prevent any non-authorized vessels from going there. There is a free tour I'd like to take sometime.
You cleared my all doubts. Thank you
Best GPS video explained i'v seen on youtube. THANK YOU SIR, APPRECIATE IT.
you doing very clear explanations ... keep up the good work ..
Cheers ali
@@CasualNavigation how does the satellite knows that the receiver has received the signal?
Well explained and illustrated, thankyou.
How does the satellite knows that the receiver has received the signal??
@@pritam9645 it doesn’t it’s just an emitter
Very clear presentation, thanks
Thanks. Again very good explanation on GPS.
Really nice job.
If you felt up to it, you could do a video on Space-Based Augmentation (SBAS) such as the WAAS system in the US or EGNOS in Europe. These are ways to augment GPS to improve performance and integrity using a network of fixed known ground-based receivers - basically an extended implementation of Differential GPS.
Great explanation! Would be even better if you can provide the link to an article which describes the distance calculation part in a bit more detail! Would love to know the mathematics behind it.
Thanks Abhishek. I'll see if I can do that for next time - add extra links for more in depth answers. Cheers for the feedback
Now I finally understand. Thank you!
Great job!
Excellent presentation: direct , progressive , and with clear graphics. As an operator, I needed to get a handle on the 'nuts and bolts' of how it works. Thank you. Very well done.
Thanks postwar46
Well explained what to do if sender and receiver have different times.
These video is really helpful sir thanks
0:10 Trilateration uses distances, triangulation use angles.
What uses angles AND distances???
That was better than any other gps vid I’ve seen. Generally I want to punch the screen. Not this time. Btw, few handheld GPS receivers are capable of dual frequency reception. SPS (standard positioning service) by L1 only is normal. L1/L2 receivers are quite a bit more expensive.
(I use gps phase differential relative baseline I geodetic surveys.)
Great job. Thanks ❤
Very good explanation.
Jeez here I was thinking my phone just measures three different boops from giant radios in earth orbit. You've clarified GPS to be quite more complicated!
Super super Thanks a million
Sir please upload more videos on maritime equipment and operations. Which r used on ships at sea.. thank you 😊🚢
This video is the best one that I have seen that explains GPS for lay users.
As Im neither a physicist or a professional navigator it is little relevance to me as to how relativistic effects affect the GPS. All I need to know is that they exist and the receiver compensates for them.
Another great video.
REQUEST: How about an update to cover GNSS.
It’s not triangulation, it trilateraration. Good video.
0:12 - Trilaterates, not triangulates.
3:02 - Typo.
5:17 - Not if your GPS receiver is a civilian model. Civilian GPS devices only use one frequency.
Also, DGPS signals are now also transmitted from geostationary satellites, in systems known as Satellite-Based Augmentation Systems, such as WAAS and EGNOS. These systems are meant to improve GPS performance in aviation applications.
Another source of GPS positioning errors happens to be the rotation of the Earth, manifested in something called the Sagnac effect.
"Civilian" psudeo-range GNSS receivers can use the L1 and L2C bands on the GPS system (that's 2 not 1); phase based systems (such ones used by land surveyors) use all the transmitted bands. If you are substituting the word GPS for GNSS then "civilian" psudeo-range receivers can use 2 bands from GPS, 2 from GLONASS and 3 from Galileo (of course if you live in the others parts of the world there are BeiDou, QZSS and IRNSS bands that can be used as well)
Great video. Can I just point out it's not a 'ring' as a distance from the satellite - it's a sphere.
very good job
Great 👍 thanks 🙏
Splendid video, great content, very well presented tothe very highest technical standard. A delight to come across. Thank you for your efforts.
Thanks Dick. Glad you enjoyed the content.
Great video
Subscribed... 🔥 🔥 🔥
you really do a good job tricking people into a physics class
Nice Video
Lovely
nice thanks
when i studied linear algebra i got so mindblown by this
super smart technology🌍
Thanks
In an old GPS Navigator I had, I think there was a geodetic correction I had (or could) apply. Am I mistaken?
Is differential gps still used in plane tracking apps?
Worth mentioning that the satellites know their positions because the reverse is happening with ground stations broadcasting their locations to the satellites.
The satellites know their position because they keep track of their own movements and every so often a ground radar station verifies it's location and a controller at Schriever AFB . This guy does not know how the system works his explanation is way off!
@@terrydouglas5008 Actually, its more of the latter (ground station uploads) than the former. While the satellites can propagate their ephemeris and predict their own position, in practice they are rarely allowed to use those results to ensure tighter operational control of the accuracy. There were studies and design trades about adding range finding hatdware and techniques, but the benefits and gains didn't outweigh the costs and risks.
@@traceythomas6761 I worked in the GPS operation center at then Falcon now Schriever Space Force Base. The operators on a set time table update the satellites positions with data received from NORAD. It was my job to maintain the two way link with the satellites. Each satellite has two three transmitters and one receiver. One channel receive/transmit is used for satellite updates.
@@terrydouglas5008 I'm not sure we're disagreeing with each other. The two-line elements are indeed calculated on the ground, just as you say, and uploaded as a broadcasting script rather than letting the satellites carry on with their own internal calculations. So even though the satellites are capable of propagating their positions for long periods (and there was a largely unused capability to let them range against each other using crosslinks), the schedule you cite basically overwrote that need. If I recall, the tempo for uploading ephemeris usually meant the next upload happened before the old set reached the "end of message", unless that tempo changed, so the broadcasts are/were basically canned. I was on the GPS Block IIF space and ground design team around the same era as the transition from Falcon to Schriever and have been on site for work with the operators in 2SOPS many times. Maybe we worked together.
i have a research to do on the subject, does anyone have more related articles or books that can help find more information.
My mind still gets boggled that the piece of glass, plastic, metal, silicon etc, aka a phone that I'm holding in my hand, can communicate all the way to a Satellite in orbit very far away
It's amazing, and mind boggling
While true of your phone, if that call is routed through a satellite, its not so much for GPS. For the latter, you're just picking up a widely available standard signal. The satellites don't receive communication from civilian receivers and have no idea you exist, much less that you're using their data to determine your position. Think of them like orbital lighthouses.
Unless you are using a sattelite phone, it is not getting any signal from any sattelite. Any position that you get from the phone, such as on Google maps, comes from cellphone towers not gps.
@@Bendigo1" it is not getting any signal from any sattelite. "
Totally wrong.
3:39 How exactly would the receiver figure out the distance between it and the satellites by adding a third satellite? Given that the offset is unknown, that part is difficult to visualize.
Also, how does the receiver know what T=0 is? I’m guessing the satellite sends the time when the transmission was sent?
This is at great video, thank you!
I often have 7 satellites acquired for high altitude kite flying. We have the World altitude record at 16,009 ft. above ground level. I use 3 different GPS units.
Great and informative video, thank you.
FYI: There was a brief time after the USA went to war against Afghanistan / Iraq following 911 that Selective Availability became a issue again due to the USA limiting access to GPS satellites, in preference of military application requirements.
Industrial scale mines in South Africa, and elsewhere, are dependent on GPS data to control the movement of massive earth moving equipment around the mines, and during the period after the initial invasion by the USA they were only picking up three GPS satellites that were available for location data.
How quickly satellite locations are changing and how many in total are in service?
Time ticks slower for a fast moving object. Otherwise, good video.
It is not triangulation, it is trilateration.
This is a big mistake and commonly misunderstood
In this case it's multilateration 'cause there is more than 3 stations.
Pretty sure it is triangulation; the distances are measured using time and speed. Trilateration uses signal strength to determine distance.
Wow, we are not worthy! There are so many smart people in this world.
Woooow
Great video, but the link is broken.
A few missing bits which are military but on the whole good video 👍
why i cant use GPS in polar water? thanks
Thank you
But wouldn't it mean that time runs slower on a satelite compared to earth? If the speed of a vehicle comes closer to lightspeed, it slows down it's interior time, doesn't it? Or is this due to less gravitational pull from the earth?
Time does run slightly slower on satellites. It is to do with the relative speeds between the observers. You can assume the observer on earth is stationary, so the satellite has a relatively high speed
There are people who deny Einsteins Theory of Relativity.
But GPS would not work correctly if it was wrong because his theory is used in the calculations and the time dilation is accounted for. If it did not exist then those corrections would make the GPS incorrect.
@@CasualNavigation
There is a time dilation effect due to the differential in height as well. Both speed and gravity contribute to this effect. Source : undergrad degree in physics
@@CasualNavigation The video has an editing error -- it says that time runs faster on the satellites due to their speed, whereas their speed would make it run slower. BUT, being not as deep in Earth's gravity well makes their time run faster. So which effect is greater?
Link you provided in the description is not working.
so sat nav is always right not the wife directions
now i got to tell her
it just tells you where you are, not where you go. But if you use google maps you should be fine
@@MenacingPerson except that one time it leads you over small roads, through tiny villages where the road is just broad enough so you don't scratch the paint and you end up in front of the chicken-coop of an old french lady because the road doesn't exist since ten years ago anymore
@@vyl4650 oddly specific. bad experience?
@@aahillakhani399 well it was somewhat annoying but also pretty funny. It was like one of these scenes in a movie. Parking in front of the coop, turning of the car and looking at each other in amused confusion. Honestly one of the best memories from that vacation
Can someone please explain who this man is? Is he a scientist or doctor? My lord the knowledge is never ending. I'd like an answer please.
Speed of light or speed of sound? Sound makes more sense to me if its using radio waves
Radio waves move at the speed of light, imagine the time it would take to get information if those waves propagated at the speed of sound.
which formula/method is used by GPS to calculate Altitude of a airplane??
The same one he explains. For a given time traveled from the 4+ satellites (there are usually at least 5 used to verify accuracy) there is only 1 location near the surface of the earth where all of the signals cross.
Keep in mind, gps altitude has errors in it due to the variances in orbital distance of the satellites, and that’s why you still need a static altimeter set to the correct barometric pressure.
@@Linusgump thank you sir
How does the GPS know where the satellites are? Do the satellites include their position when they broadcast the time, or does the GPS keep an almanac of where every satellite should be at all times?
Can GPS devices that have network access download the almanac from the internet, or do they rely on receiving it directly from the satellites? Also, is there one almanac per satellite or does each almanac have data on the whole constellation?
7:34 This is VERY wrong. Just due to the speed the clocks are running SLOWER on the satellites... but then you need to mention mention gravity, which you missed completely, because they are in slightly lower gravity the clocks run faster. So you have to add both effects up and constantly adjust for it. I think it drifts off about 10 km a day cumulatively. There's an office in the US military that all they do is compensate for this all day
do ou know algorithm?... How reciever knows the total wave travel time...even though there is one way signal transmission?
The wave emitted from the satellite is modulated, giving the name of the satellite, the time sent, non-precise position of the satellite etc
@@danielthomas9086 thankyou but gps module doesn't come. With etc... Still didn't get
As stated tje sat signal is always saying what time it is. And also contains modulation data with satellite orbital predictions. The modulated data is a slow transfer so may cause an initial delay before a solution is computed.
How does the satellite know it's location??
Its important to remember that time is more flexible than most people realize. Two people on different latitudes will arrive at the same longitudinal point at the exact same time, but travelled different distances to get there. Imagine someone 1 meter from the south pole and someone on the equator. The variable allowing for both to arrive at the same time is time itself being experienced differently in relation to their velocity. Also, and not mentioned in the video (or I missed it) is the impact of gravity on time. The Earth is not a uniform push down on everywhere. The push down can be different over certain spots versus others depending on what is in the ground etc.
What's with blurry blobs representing buildings?
Talk about one Satellite,
It look like we thraw a rock in to a cave, it will response an echo and we will count the time to calculate the deep.
But some body please explain me how Smartphone or Satellite know the that time signal came? (because I think the Smartphone is unable to send any signal back to Satellite)
Yeesss, I have sammmeee doubtt!! Please somebody respond!
I expected the potential errors to include something about the weird shape of the earth (distorted sphere, slightly ovaloid, if I remember correctly).
GPS positioning measurements don't give you direct lat and longs. They give you xyz coordinates in a 3D grid that are then projected onto an ellipsoid (the mathematical model of a squished sphere), and are converted to lat, long, and height above the ellipsoid.
Correction: gps do not work on triangulation rather trilateration method.
Multilateration for aviation gps because we need 4 stations minimum to shoot a LPV approach
I left Endomondo ON after I came home and after 4 hours I did 5 kilometers and burned 600 calories.
Isn't the resistance to the signals by the (different layers of the) atmosphere always the same so you can subtract it!?
If the receiver's battery is depleted its clock will stop working. If the battery is recharged later the receiver will work again, but its clock will no longer be synchronized with the sitellite's clocks. How do receivers synchronize their clocks with satellite's clocks?
So you are saying that you are an idiot that’s why satellites are fake?
@@tgstudio85, I never said satellites were fake. They are real. My question was about GPS receivers.
Its the fourth satellite as 3 give you fix with error induced by local clock fourth then is then able to calculate basically your exact moment in time from the error . If we had atomic clock synchronised on our receiver then we would get fix with only 3 satellites but we can't
The video totally screws up the relativistic effects. It ignores General Relatively entirely even though it causes (due to reduced gravity) the greatest deviation on satellite clocks (+46 microseconds per day). The video only mentions the effects of Special Relatively (-7 microseconds daily due to satellite velocity). The SR high velocity makes the orbiting clocks "SLOWER", while GR low gravity makes orbital clocks run "FASTER." The GR speeding is about six times that of SR slowing, producing a net value of about +39 microseconds which is why orbital clocks are programed to run slow by this amount.
2022
Darn you, Algebra 😠 turns out there is a real practical use for you
Absolutely! Darn you Algebra! Thankfully we have clever people to calculate all of this for us. So my time in school giving laxatives to the girls and getting bullied by the aforementioned females was not totally wasted.
I still don't understand how "a" (the time error) is calculated
GPS uses trilateration not triangulation.
It's actually not a ring but sphere
Trilateration not triangulation.
How does the satellite knows that the receiver has received the signal?
Ok you need to stip eith using logoes in ur examples its getting snnoying with the blurry stuff
Hi
I'm sure you already know what GPS is.
But have you ever wondered how GPS is?
Everyone always asks what GPS is but no-one asks how GPS is...
XD
The one good thing that Bill Clinton did was to order the selective availability turned off on May 4 2000 (from memory). When I heard the news on the TV I went outside with my ancient Panasonic G5500 - only takes 20 minutes to get a fix - and was astonished to see the increased precision. I later bought a Magellan and had all the datum and transformation options, that really made GPS useful for everybody. We won't mention Monica....
GPS is a ground based system LORAN (Long range hyperbolic radio navigation system) proved this decades ago with a ground range of up to 2400km no satellites required, obviously since WWII the infrastrcture and technology have improved and public GPS frequencies are open on all cell towers. the towers never move and that is how we get very accurate positioning on GPS enabled devices. cell signal and GPS are basically the same technology just running at different frequencies, the GPS frequencies are lower and travel further. obviously there are other factors such as the size and power of your hardware, satelite phones are just normal mobile phones but with better hardware designed to achieve greater range. obviously marine industry navegation tech is more powerful still.
No.
@@Bendigo1 ...and thrice no.