how does gps even work

[apoyusiken]

i mean think about it. there are so many devices connected to gps. how do satellites keep up? (i am talking about the cpu workload) 

 

also unrelated, how do the satellites send and receive data? what about the receivers here on earth?

[TetraSky]

Often time, the "gps" you have is not even satellite based.

On your phone, the "gps" is more likely cell tower based. Where as with multiple cell tower in an area, your phone can triangulate your position through a bunch of maths based on your distance from each towers. This is how you can get pinpoint accuracy for map location.

But if you're out and about far from multiple cell towers... You will often time find out that your location is not exactly accurate. Because satellite based GPS for us normies is not super accurate. Still better than nothing.

[manikyath]

the cpu workload i dont presume is much worse than just the upkeep of a cell signal. the "consumer" version of GPS is also very much a "lite" version of what it does for the US army, apparently...

 

for the rest of it, wikipedia has a pretty good writeup, very abbreviated: it's a bunch of standardized messages on the UHF radio band.

https://en.wikipedia.org/wiki/GPS_signals

 

2 minutes ago, TetraSky said:

Where as multiple cell tower in an area can triangulate your position through a bunch of maths based on your distance from each tower.

that's exactly what GPS does too, just with satalites instead of cell towers.

also.. is this why my old phone's google maps had absolutely no idea where i was? living in a relatively rural area with very little overlap between cell towers...

[apoyusiken]

3 minutes ago, manikyath said:

overlap

overlap doesnt matter but you need 4 towers

[whispous]

1 hour ago, apoyusiken said:

how do satellites keep up?

They key thing to know is that your GPS device is not speaking to the satellites, and the satellites are not listening.

 

The satellites speak, and your device listens - it's one way communication.

 

GPS satellites transmit signals and using the difference in time between signals from several satellites at once, your device figures out it's own co-ordinates.

 

 

 

https://en.wikipedia.org/wiki/Global_Positioning_System#Principles

[wanderingfool2]

1 hour ago, apoyusiken said:

i mean think about it. there are so many devices connected to gps. how do satellites keep up? (i am talking about the cpu workload) 

 

also unrelated, how do the satellites send and receive data? what about the receivers here on earth?

It's not that there are a lot of devices connected to GPS...it's that there are a lot of devices that are using the GPS signal.

 

It's like wayfinding based on the stars.  You can reliably tell where you are on the Earth's surface just based on where the stars are in the sky etc.  The stars aren't doing the work, you are just working based on where the stars are.

 

GPS is very similar.  In effect what the GPS will do is send out a nice broadcast signal on a specific frequency with the current time along with which satellite it is.  The thing is we know orbital mechanics quite well and can predict where an object will be based on just the time and starting position of the satellite.  So each time you receive a signal you can calculate where in 3d space the satellite is.  Now the thing is you don't necessarily "know" how long the signal has been travelling to you.  So you will need another satellite's time, and eventually you build up enough "times" and positions in 3d space and you can effectively triangulate where you are (compensating for time).

 

So in reality the GPS sats don't really have to do much work except making sure their clocks are running accurately.

 

As for how satellites send and receive data, well it's similar to how cell phones work...except in this case instead of sending the signal every which way to the cell tower, you use a directional broadcaster.  It's why you used to have sat dishes with large U looking things.  It takes a very weak signal from one direction and essentially only looks at a specific point [like a telescope really].  Sats of old also had similar things to capture the weak signals sent from Earth.

[apoyusiken]

27 minutes ago, whispous said:

They key thing to know is that your GPS device is not speaking to the satellites, and the satellites are not listening.

 

The satellites speak, and your device listens - it's one way communication.

 

GPS satellites transmit signals and using the difference in time between signals from several satellites at once, your device figures out it's own co-ordinates.

 

 

 

https://en.wikipedia.org/wiki/Global_Positioning_System#Principles

thanks this was enough info

[apoyusiken]

17 minutes ago, wanderingfool2 said:

It's not that there are a lot of devices connected to GPS...it's that there are a lot of devices that are using the GPS signal.

 

It's like wayfinding based on the stars.  You can reliably tell where you are on the Earth's surface just based on where the stars are in the sky etc.  The stars aren't doing the work, you are just working based on where the stars are.

 

GPS is very similar.  In effect what the GPS will do is send out a nice broadcast signal on a specific frequency with the current time along with which satellite it is.  The thing is we know orbital mechanics quite well and can predict where an object will be based on just the time and starting position of the satellite.  So each time you receive a signal you can calculate where in 3d space the satellite is.  Now the thing is you don't necessarily "know" how long the signal has been travelling to you.  So you will need another satellite's time, and eventually you build up enough "times" and positions in 3d space and you can effectively triangulate where you are (compensating for time).

 

So in reality the GPS sats don't really have to do much work except making sure their clocks are running accurately.

 

As for how satellites send and receive data, well it's similar to how cell phones work...except in this case instead of sending the signal every which way to the cell tower, you use a directional broadcaster.  It's why you used to have sat dishes with large U looking things.  It takes a very weak signal from one direction and essentially only looks at a specific point [like a telescope really].  Sats of old also had similar things to capture the weak signals sent from Earth.

well, we could listen to waves from space too right? are we not sensitive enough?

[DeerDK]

16 hours ago, apoyusiken said:

i mean think about it. there are so many devices connected to gps. how do satellites keep up? (i am talking about the cpu workload) 

 

also unrelated, how do the satellites send and receive data? what about the receivers here on earth?

Satellites sends out a signal, that the device picks up. It's like with a radio tower, the signal doesn't get weaker just because you put up some more radios listening to the signal. 

 

They work by knowing the satellite position and the signal contains code that makes calculating the distance from the satellite to your device possible. So it's like drawing a circle with the satellite as center, do that with enough satellites and you can see your position from where all the circles intersect. 

Somewhat simplified

 

Remember, it was originally designed for soldiers to navigate by. Not good if they could get tracked, so it had to be a passive receiver 

[thewelshbrummie]

15 hours ago, whispous said:

They key thing to know is that your GPS device is not speaking to the satellites, and the satellites are not listening.

 

The satellites speak, and your device listens - it's one way communication.

 

GPS satellites transmit signals and using the difference in time between signals from several satellites at once, your device figures out it's own co-ordinates.

 

 

 

https://en.wikipedia.org/wiki/Global_Positioning_System#Principles

This. It's like OTA TV signals, the signal is broadcast, your device just picks it up and the transmitter the signal is broadcast from doesn't receive anything. So you can have one broadcast signal and effectively an infinite number of TVs receiving that signal. And the cost to the broadcaster is the same if they have 1 viewer or 1,000,000 viewers, it's the same cost.

 

Streaming is different - it's bandwidth x number of viewers which is why streaming video dominates Internet traffic.

[wanderingfool2]

16 hours ago, apoyusiken said:

well, we could listen to waves from space too right? are we not sensitive enough?

I don't know what you mean by this?  What do you mean listen to waves from space?

 

If you are talking about 3d positioning based on other signals from space...that doesn't quite work in that you need to really know where the satellite is in 3d space and time in order to really triangulate where you are.  You can still roughly do it though with stars (iirc some space crafts use that to track where they are/align correctly)...but it can only really give so much information that way

[apoyusiken]

11 minutes ago, wanderingfool2 said:

I don't know what you mean by this?  What do you mean listen to waves from space?

 

If you are talking about 3d positioning based on other signals from space...that doesn't quite work in that you need to really know where the satellite is in 3d space and time in order to really triangulate where you are.  You can still roughly do it though with stars (iirc some space crafts use that to track where they are/align correctly)...but it can only really give so much information that way

what about finding relative position?

[aggie113]

GPS is all about timing

 

[manikyath]

18 hours ago, apoyusiken said:

overlap doesnt matter but you need 4 towers

there arent 4 towers in my area. that's what i meant with overlap.

[wanderingfool2]

48 minutes ago, apoyusiken said:

what about finding relative position?

GPS is all about effectively finding the relative position though.  You can't just use any old signal because you lack the basic information of where the signal was coming from.

 

In theory you could make one that used an antenna that was capturing directionality as well, but that would I guess would require a large antenna and massive amounts of circuitry and latest processing.

[Kisai]

19 hours ago, apoyusiken said:

i mean think about it. there are so many devices connected to gps. how do satellites keep up? (i am talking about the cpu workload) 

 

also unrelated, how do the satellites send and receive data? what about the receivers here on earth?

GPS is broadcasting from 24 for satellites in Medium Earth Orbit (MEO.) GLONASS and Galileo also do.

 

Your device never connects to them, it only receives data. Your phone only needs to be able to see 3 of them to find it's 2D coordinates, and needs 4 to get a 3D location. But you must have a clear view of the sky.

 

What your Cell phone actually has is A-GPS, which is done with cell phone towers but is only precise down to about 100 meters or 300ft. Satellite GPS is precise down to about 3 meters if it can see 4+ satelites but it depends on weather and buildings around.

 

That said, I've had some of the first gen USB GPS stuff, a Nokia N95, and every iPhone I've had has had GPS support. It's kind of unobvious how GPS is used unless you look into it.

 

On an iPhone "Precise Location" uses your WiFi and bluetooth as location points.

 

In most cases the actual satellite GPS is probably not being used until you are outside of a city when it can see 5 of them. Like the Nokia N95 required being able to see 5 to lock on, but only needed 3 to actually show a position on the map. The USB receiver that came with Microsoft Steets and Maps from like, 2004 was a 3" device that you stick to your windshield, and could see around 12 IIRC.

 

it uses less power to rely on the radios that are already turned on for other reasons.

 

All GPS does is, in an over-simplification, is send the time and it's orbital information and the "gps device" in your computer/phone gets several of these to figure out the coordinates from the deltas in the time from the constellation position.

 

The same with using A-GPS from Cellular towers, and WiFi/Bluetooth.  If you've ever gone "war driving" back when WiFI was new, you could figure out where a WiFi access point was from about 1000m away if there was nothing obstructing it. So in that case it uses the signal strength.

 

[apoyusiken]

14 minutes ago, Kisai said:

GPS is broadcasting from 24 for satellites in Medium Earth Orbit (MEO.) GLONASS and Galileo also do.

 

Your device never connects to them, it only receives data. Your phone only needs to be able to see 3 of them to find it's 2D coordinates, and needs 4 to get a 3D location. But you must have a clear view of the sky.

 

What your Cell phone actually has is A-GPS, which is done with cell phone towers but is only precise down to about 100 meters or 300ft. Satellite GPS is precise down to about 3 meters if it can see 4+ satelites but it depends on weather and buildings around.

 

That said, I've had some of the first gen USB GPS stuff, a Nokia N95, and every iPhone I've had has had GPS support. It's kind of unobvious how GPS is used unless you look into it.

 

On an iPhone "Precise Location" uses your WiFi and bluetooth as location points.

 

In most cases the actual satellite GPS is probably not being used until you are outside of a city when it can see 5 of them. Like the Nokia N95 required being able to see 5 to lock on, but only needed 3 to actually show a position on the map. The USB receiver that came with Microsoft Steets and Maps from like, 2004 was a 3" device that you stick to your windshield, and could see around 12 IIRC.

 

it uses less power to rely on the radios that are already turned on for other reasons.

 

All GPS does is, in an over-simplification, is send the time and it's orbital information and the "gps device" in your computer/phone gets several of these to figure out the coordinates from the deltas in the time from the constellation position.

 

The same with using A-GPS from Cellular towers, and WiFi/Bluetooth.  If you've ever gone "war driving" back when WiFI was new, you could figure out where a WiFi access point was from about 1000m away if there was nothing obstructing it. So in that case it uses the signal strength.

 

bro ok thx but this is resolved

[DeerDK]

2 hours ago, Kisai said:

GPS is broadcasting from 24 for satellites in Medium Earth Orbit (MEO.) GLONASS and Galileo also do.

 

Your device never connects to them, it only receives data. Your phone only needs to be able to see 3 of them to find it's 2D coordinates, and needs 4 to get a 3D location. But you must have a clear view of the sky.

 

What your Cell phone actually has is A-GPS, which is done with cell phone towers but is only precise down to about 100 meters or 300ft. Satellite GPS is precise down to about 3 meters if it can see 4+ satelites but it depends on weather and buildings around.

 

That said, I've had some of the first gen USB GPS stuff, a Nokia N95, and every iPhone I've had has had GPS support. It's kind of unobvious how GPS is used unless you look into it.

 

On an iPhone "Precise Location" uses your WiFi and bluetooth as location points.

 

In most cases the actual satellite GPS is probably not being used until you are outside of a city when it can see 5 of them. Like the Nokia N95 required being able to see 5 to lock on, but only needed 3 to actually show a position on the map. The USB receiver that came with Microsoft Steets and Maps from like, 2004 was a 3" device that you stick to your windshield, and could see around 12 IIRC.

 

it uses less power to rely on the radios that are already turned on for other reasons.

 

All GPS does is, in an over-simplification, is send the time and it's orbital information and the "gps device" in your computer/phone gets several of these to figure out the coordinates from the deltas in the time from the constellation position.

 

The same with using A-GPS from Cellular towers, and WiFi/Bluetooth.  If you've ever gone "war driving" back when WiFI was new, you could figure out where a WiFi access point was from about 1000m away if there was nothing obstructing it. So in that case it uses the signal strength.

 

And then we can start talking about RTK