This is the same method that sextant, compass & chronometer was used for navigation going back 250 years. Using star charts known stars are measured for angle by sextant & the 3 intersecting circles are drawn. I've even seen 2 circles used because usually a navigator knows approximately where he is & the other 2 circle intersection are weeks of sailing distance away. Navigation tutorials on it all can be seen right here on You Tube.
While i worked on GPS silicon I met a guy (ION Fellow) who told me that with a good almanac and chronometer he could place himself on the face of the Earth within like 1 NM. Old technique! … but adding atomic clock accuracy and good math models you can get cm or even mm-level accuracy. We all stand on the shoulders of giants !
@hugh more Wrong, a GPS receiver does not measure any angle the way a sextant does. The GPS location solution is found by trilateration and not triangulation as claimed in the video title.
very clear explanation! thank you for the video. Just two questions: after the calculation of the distamce d, what is done after?How do we get the form AºB'C''D that helps us to locate a point in the map?
Essentially, the receiver calculates the distance to at least 4 satellites. The satellites beam down their position on a continual basis and we adjust the distance calculated from the time difference between the satellite and the receiver. Then we adjust it for time abberations, ionosphere and troposphere effects and correlate the 4 measurements.
It's easier to think that the receiver has no time source and it's trying to locate itself in a 4-dimensional space: X Y Z T, with T for time, therefore you need 4 distances.
Can you explain how the delta t is calculated specifically? If there ara an absolute need for perfect accuracy in the time mesurements, how can a gps receiver calculate this uncertainty and essencially eliminate the time error? Thank you
In the video you mentioned that the distance from the object to satellites were d1, d2, d3 respectively. So wouldn't be the position of the object be at the intersection of all three circles with radius d1, d2, d3?
Triangulation ?????? Triangulation means working with angles which is waaaaaaaaaaaaaay too inaccurate. GNSS use trilateration which means using DISTANCES berween satellites and Rx antenna (by using propagation delays) which is by far more accurate.
This receiver's time error named delta t there... could it include relativity's time dilation induced error (supposing the satellite dont compensate for it). I feel like as long as we have 4 satellites, we are good, and as long as the 4 satellites are in time sync with each other.
The initial videos are just some basic concepts. The details, including adjustment for relativity, and the need for a fourth satellite are explained in details in the rest of the videos in this playlist.
We use 3 satellites to determine the position in the x, y, and z directions and a fourth satellite to correct for time in order to make the x, y, and z positions more accurate.
Hello, I'm not 100% sure but I think what is explained in this video is kind of wrong. When we have the distance to the second satellite, and we draw the circle where we could be at is not correct (i believe). This is because not all points in that circle meet the requirement of being d1 from satellite1 and d2 from satellite2, in fact, only 2 points meet those requirements, the intersection of both spheres. And then, when we add the 3rd sphere we can narrow it down to 1 point. Anyway, thank you for these videos, they are really useful.
you have to remember that even though this is drawn 2d, the satellites work in 3d space. The first satellite only knows a single distance, but not any direction. This means you can be in a sphere around the satellite (it's drawn as a circle though). The second satellite gives another sphere around it. Combining these two spheres means that you are in a circle where the two spheres intersect. from above it would look like a line between the two intersection points. The third satellite gives a third sphere. Combining the three gives you the final two points. Unlike he said though, from above the two points would look like one since one is on the ground and one is directly above it far out in space. The one is space is discarded because you are obviously not in space.
Hey, thank you very much for the detailed answer, unlike the other one. However I had already figured out what was the issue, I just didn't bother responding to those 4 words. It's exactly like you said. The explanation in the video is correct but the drawing is kind of wrong, due to being drawn in 2D, and that's what got me confused. Thank you anyway!
Hey...do you have a moment to entertain a question about using triangulation to measure distances from ground level to space...I'm absolutely horrible with geometry/math and am stumped on something.
I still have questions about how does the receiver get accurate time. my presumption is that the receiver simply assume first satellites is direct over head (20200km) and deduct time travelling to get a nearly accurate time, then base on time difference to calculate other two satellites distance. Here comes the fourth satellite to match the previous satellites calculation and adjust receivers time by one nanosecond increment to make the fourth satellite's sphere 'barely' touch the ellipsoid calculated by previous three satellite. Is this correct?
To add on to the question, sir, you haven't explained how exactly do we get "delta t" using the fourth satellite. This is the question bugging me. Since, no matter how many satellites we use,the error of the receiver clock will always remain inherent to it and the distances thus calculated will be wrong. Can you please explain how the fourth satellite eliminates the receiver clock error?
@@hdgala I believe two methods are commonly used. One method is to adjust the clock in the receiver in small increments until the error is reduced to a minimum, the other is as follows: For each of the 4 satellites you can construct an equation giving the position of the satellite, the receiver, and the time difference. When you have (at least) 4 satellites then these can be solved for the time difference. mason.gmu.edu/~treid5/Math447/GPSEquations/ explains this in detail.
i have garmin dakota gps and it can work at least with 5 satelites, with 3 or 4 it does not where is, few times it searched for 5. satelite more than 5 minutes, and on some same area all satelites have weak signal- how it is possible if satelites changes its positions- are not geostational
GPS tracks the satellites as they move across the sky. That makes it easier for the GPS to determine the exact position. If they are geosynchronous then it would be very difficult to find the exact position.
@@MichelvanBiezen thank you, but why on same position is weak signal( it is on 500m elevation and there is no obstracles for satelites, even in aircraft that flies on 5000m is same story with weak signal) that my dakota can not know where it is: i travel by car on highway in westbound direction and no problems, but in east bound direction on same position it is lost , it shows that i move in backward, i have track recorded and it looks like zig zag forward backward, but i drive straight
There could be a number of reasons. There can be something wrong with the algorithms used, there can be something wrong with the software, there could be something wrong with the receiver, or it can be weather conditions or conditions in the ionosphere. Most GPS do not compensate sufficiently for changes in the ionosphere.
@@MichelvanBiezen it started to be confused on position : n45*29.586minutes, e015*26.804 minutes, it is on highway in east bound next 15 kilometers, allways on same portion, in aeroplane is very good proffesional garmin 520 gps (it works good and has no problems but is feels weak signal ), it is logical if satelites are not stationary weak signal spots should be allways on different places not on same spot no matter of day-night, summer-winter, wind-com
TRIANGULATION - find a location from three angle measurements TRILATERATION - find a location from three distance measurements The video title is misleading because neither GPS satellites nor GPS receivers measure angles. A true title should be QUADRILATERATION - find a location and time correction from 4 distance measurements.
I think, the video is not correct. 1 antenna: I know the position on the circle, 2 antenna: I know the position where the circles intersect (normaly 2 points, can be one point), 3 antennas: I know the exact position. Based on the time the signal will run, so I know the radius of the circles
So it was explained to me in other material a little bit differently. So I am sort of confused. One example is when you have two satellites, it means you are at one of two spots, not the circle as your video implies....so im not sure who is correct.....it would have been nice to see numbers and examples, and more detailed explanation...
This is trilateration not triangulation.
much thanks ;) i was looking for the word
Andreea Gheorghita, People always confusing the two, amazing.
Fuck me up with that knowledge
And if you have more than those three distances (since most of the time you have more GPS satellites locked), you have multilateration
This is the same method that sextant, compass & chronometer was used for navigation going back 250 years. Using star charts known stars are measured for angle by sextant & the 3 intersecting circles are drawn. I've even seen 2 circles used because usually a navigator knows approximately where he is & the other 2 circle intersection are weeks of sailing distance away.
Navigation tutorials on it all can be seen right here on You Tube.
While i worked on GPS silicon I met a guy (ION Fellow) who told me that with a good almanac and chronometer he could place himself on the face of the Earth within like 1 NM. Old technique! … but adding atomic clock accuracy and good math models you can get cm or even mm-level accuracy.
We all stand on the shoulders of giants !
@hugh more Wrong, a GPS receiver does not measure any angle the way a sextant does. The GPS location solution is found by trilateration and not triangulation as claimed in the video title.
very clear explanation! thank you for the video. Just two questions: after the calculation of the distamce d, what is done after?How do we get the form AºB'C''D that helps us to locate a point in the map?
Essentially, the receiver calculates the distance to at least 4 satellites. The satellites beam down their position on a continual basis and we adjust the distance calculated from the time difference between the satellite and the receiver. Then we adjust it for time abberations, ionosphere and troposphere effects and correlate the 4 measurements.
We plan on adding more videos on how all that works.
It's easier to think that the receiver has no time source and it's trying to locate itself in a 4-dimensional space: X Y Z T, with T for time, therefore you need 4 distances.
That's a great way to think about it
Can you explain how the delta t is calculated specifically? If there ara an absolute need for perfect accuracy in the time mesurements, how can a gps receiver calculate this uncertainty and essencially eliminate the time error? Thank you
That is all explained in the videos in this playlist. In order to also determine the time error, the receiver will need a fourt satellite.
In the video you mentioned that the distance from the object to satellites were d1, d2, d3 respectively. So wouldn't be the position of the object be at the intersection of all three circles with radius d1, d2, d3?
Yes, if you presume that these distances can be determined accurately. There will be errors that need to be accounted for.
@Ik No. They aren't circles, they are spheres.
@@MrCuddlyable3but isnt that how the position is calculated? If not, how is it actually calculated?
T R I L A T E R A T I O N !!!
Yes, you are correct.
@@MichelvanBiezen Shame on you Sir for leaving the misleading title uncorrected after knowing for over a year that GPS does not employ triangulation.
Triangulation ??????
Triangulation means working with angles which is waaaaaaaaaaaaaay too inaccurate. GNSS use trilateration which means using DISTANCES berween satellites and Rx antenna (by using propagation delays) which is by far more accurate.
This receiver's time error named delta t there... could it include relativity's time dilation induced error (supposing the satellite dont compensate for it). I feel like as long as we have 4 satellites, we are good, and as long as the 4 satellites are in time sync with each other.
The initial videos are just some basic concepts. The details, including adjustment for relativity, and the need for a fourth satellite are explained in details in the rest of the videos in this playlist.
Clear and logical explanation. Ps. I like your yellow bow tie!
Glad you like it!
So what he said is Trilateration not triangulation.
Trilateration computation deals with distances and triangulation deals with angular measurements
Exactly. Somehow weird a person using the wrong expressions while trying to explain something. Even the bow is not aligned properly...
How does GPS calculate our altitude? Also because the time for the transmission will take less for higher altitudes?
We use 3 satellites to determine the position in the x, y, and z directions and a fourth satellite to correct for time in order to make the x, y, and z positions more accurate.
🙏🙏🙏🌎 pagers physics. Truth beginning. All knowing God
Glad you find this fascinating.
Hello, I'm not 100% sure but I think what is explained in this video is kind of wrong.
When we have the distance to the second satellite, and we draw the circle where we could be at is not correct (i believe). This is because not all points in that circle meet the requirement of being d1 from satellite1 and d2 from satellite2, in fact, only 2 points meet those requirements, the intersection of both spheres. And then, when we add the 3rd sphere we can narrow it down to 1 point.
Anyway, thank you for these videos, they are really useful.
+Peng
The video is correct.
you have to remember that even though this is drawn 2d, the satellites work in 3d space. The first satellite only knows a single distance, but not any direction. This means you can be in a sphere around the satellite (it's drawn as a circle though).
The second satellite gives another sphere around it. Combining these two spheres means that you are in a circle where the two spheres intersect. from above it would look like a line between the two intersection points.
The third satellite gives a third sphere. Combining the three gives you the final two points. Unlike he said though, from above the two points would look like one since one is on the ground and one is directly above it far out in space. The one is space is discarded because you are obviously not in space.
Hey, thank you very much for the detailed answer, unlike the other one. However I had already figured out what was the issue, I just didn't bother responding to those 4 words.
It's exactly like you said. The explanation in the video is correct but the drawing is kind of wrong, due to being drawn in 2D, and that's what got me confused. Thank you anyway!
No problem!
Hey...do you have a moment to entertain a question about using triangulation to measure distances from ground level to space...I'm absolutely horrible with geometry/math and am stumped on something.
I still have questions about how does the receiver get accurate time. my presumption is that the receiver simply assume first satellites is direct over head (20200km) and deduct time travelling to get a nearly accurate time, then base on time difference to calculate other two satellites distance. Here comes the fourth satellite to match the previous satellites calculation and adjust receivers time by one nanosecond increment to make the fourth satellite's sphere 'barely' touch the ellipsoid calculated by previous three satellite. Is this correct?
It is actually more complicated than that as they adjust for relativistic effects and the gravitational effects which also affects time.
satellites are time synchronized
To add on to the question, sir, you haven't explained how exactly do we get "delta t" using the fourth satellite. This is the question bugging me. Since, no matter how many satellites we use,the error of the receiver clock will always remain inherent to it and the distances thus calculated will be wrong. Can you please explain how the fourth satellite eliminates the receiver clock error?
@@hdgala I believe two methods are commonly used. One method is to adjust the clock in the receiver in small increments until the error is reduced to a minimum, the other is as follows:
For each of the 4 satellites you can construct an equation giving the position of the satellite, the receiver, and the time difference. When you have (at least) 4 satellites then these can be solved for the time difference.
mason.gmu.edu/~treid5/Math447/GPSEquations/ explains this in detail.
what are the calculation
Good 👍👍
Thank you
i have garmin dakota gps and it can work at least with 5 satelites, with 3 or 4 it does not where is, few times it searched for 5. satelite more than 5 minutes, and on some same area all satelites have weak signal- how it is possible if satelites changes its positions- are not geostational
GPS tracks the satellites as they move across the sky. That makes it easier for the GPS to determine the exact position. If they are geosynchronous then it would be very difficult to find the exact position.
@@MichelvanBiezen thank you, but why on same position is weak signal( it is on 500m elevation and there is no obstracles for satelites, even in aircraft that flies on 5000m is same story with weak signal) that my dakota can not know where it is: i travel by car on highway in westbound direction and no problems, but in east bound direction on same position it is lost , it shows that i move in backward, i have track recorded and it looks like zig zag forward backward, but i drive straight
There could be a number of reasons. There can be something wrong with the algorithms used, there can be something wrong with the software, there could be something wrong with the receiver, or it can be weather conditions or conditions in the ionosphere. Most GPS do not compensate sufficiently for changes in the ionosphere.
@@MichelvanBiezen it started to be confused on position : n45*29.586minutes, e015*26.804 minutes, it is on highway in east bound next 15 kilometers, allways on same portion, in aeroplane is very good proffesional garmin 520 gps (it works good and has no problems but is feels weak signal ), it is logical if satelites are not stationary weak signal spots should be allways on different places not on same spot no matter of day-night, summer-winter, wind-com
Nice sir.
Thanks and welcome
Ok, bad install or setting for chronyc in small usb gps and linux, no sync of time, no position :/
Sort of knowing where the problem is, thanks :)
You know what you did is the union/ intersection of all three sets
TRIANGULATION - find a location from three angle measurements
TRILATERATION - find a location from three distance measurements
The video title is misleading because neither GPS satellites nor GPS receivers measure angles. A true title should be QUADRILATERATION - find a location and time correction from 4 distance measurements.
I think, the video is not correct. 1 antenna: I know the position on the circle, 2 antenna: I know the position where the circles intersect (normaly 2 points, can be one point), 3 antennas: I know the exact position. Based on the time the signal will run, so I know the radius of the circles
@Horst Christoph Schreiber You are thinking in 2D. Think in 3D !
So it was explained to me in other material a little bit differently. So I am sort of confused. One example is when you have two satellites, it means you are at one of two spots, not the circle as your video implies....so im not sure who is correct.....it would have been nice to see numbers and examples, and more detailed explanation...
If you take earth as a third sphere you will find only 2 points not circle
This is not triangulation
cool
🙂
the delta t explanation was terrible and rushed
Thanks for the input.