The GPS

Quote from: jroa on May 10, 2015, 07:25:30 PM

Actually, a line of sight signal does need relays if the receiver is not in the line of sight.  To use your own words, Duh.

True for some things like voice or data,  but not true for GPS,  GPS relies on the precise time difference of signals from different transmitters to triangulate the reciever position.  So GPS will ONLY work when there is a direct line of sight between transmitters and receivers.    GPS won't work through a relay.

The GPS system would not work without satellites.

Ground based positioning was in use decades before GPS.  See Loran.

Quote from: Rayzor on May 10, 2015, 07:46:05 PM

Quote from: jroa on May 10, 2015, 07:25:30 PM

Actually, a line of sight signal does need relays if the receiver is not in the line of sight.  To use your own words, Duh.

True for some things like voice or data,  but not true for GPS,  GPS relies on the precise time difference of signals from different transmitters to triangulate the reciever position.  So GPS will ONLY work when there is a direct line of sight between transmitters and receivers.    GPS won't work through a relay.

The GPS system would not work without satellites.

Ground based positioning was in use decades before GPS.  See Loran.

Neither Loran or GPS can work with relays.

Loran has a very small number of transmitters relative to the huge number required for global coverage and is only suitable for high population locations that justify the already large number of transmitters.

Both loran and GPS require that the real position of the transmitter is known to the receiver.

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

Not yet apparently.  Loran is still being developed?

People are worried that for low cost it is possible to mimic GPS satellites to cause receivers to produce false information

http://www.digitaltrends.com/mobile/gps-spoofing/

Using a laptop, a small antenna and an electronic GPS “spoofer” built for $3,000, GPS expert Todd Humphreys and his team at the University of Texas took control of the sophisticated navigation system aboard an $80 million, 210-foot super-yacht in the Mediterranean Sea.

Bit of a mystery to me at the moment how they can do that though

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

Not yet apparently.  Loran is still being developed?

Well, it seems to be in it's death throes:

In November 2009, the USCG announced that LORAN-C is not needed by the U.S. for maritime navigation. This decision left the fate of LORAN and eLORAN in the U.S. to the Secretary of the Department of Homeland Security. Per a subsequent announcement, the U.S. Coast Guard, in accordance with the DHS Appropriations Act, terminated the transmission of all U.S. LORAN-C signals on 8 February 2010. On 1 August 2010 the U.S. transmission of the Russian American signal was terminated, and on 3 August 2010 all Canadian signals were shut down by the USCG and the CCG.

The European Union had decided that the potential security advantages of Loran are worthy not only of keeping the system operational, but upgrading it and adding new stations. This is part of the wider Eurofix system which combines GPS, Galileo and nine Loran stations into a single integrated system.

However, Norway announced in late 2014 that all of its remaining transmitters, which make up a significant part of the Eurofix system, will be shut down on 1 January 2016.

It seems the bits that are left integrate GPS into the system anyway.

Bit of a mystery to me at the moment how they can do that though

Well, there is still no real-world example ever recorded.  For the proof of concept test involving the yacht, the students were actually aboard the yacht with the equipment - hardly a realistic example.

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

And how do you think it does this?  Try it with GPS and wireless turned off, then come back to us.

Quote from: Aliveandkicking on May 11, 2015, 05:03:00 AM

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

Not yet apparently.  Loran is still being developed?

Well, it seems to be in it's death throes:

Quote

In November 2009, the USCG announced that LORAN-C is not needed by the U.S. for maritime navigation. This decision left the fate of LORAN and eLORAN in the U.S. to the Secretary of the Department of Homeland Security. Per a subsequent announcement, the U.S. Coast Guard, in accordance with the DHS Appropriations Act, terminated the transmission of all U.S. LORAN-C signals on 8 February 2010. On 1 August 2010 the U.S. transmission of the Russian American signal was terminated, and on 3 August 2010 all Canadian signals were shut down by the USCG and the CCG.

The European Union had decided that the potential security advantages of Loran are worthy not only of keeping the system operational, but upgrading it and adding new stations. This is part of the wider Eurofix system which combines GPS, Galileo and nine Loran stations into a single integrated system.

However, Norway announced in late 2014 that all of its remaining transmitters, which make up a significant part of the Eurofix system, will be shut down on 1 January 2016.

It seems the bits that are left integrate GPS into the system anyway.

Quote

Bit of a mystery to me at the moment how they can do that though

Well, there is still no real-world example ever recorded.  For the proof of concept test involving the yacht, the students were actually aboard the yacht with the equipment - hardly a realistic example.

All they have to do is rebroadcast the very weak satellite signals at a stronger signal than received from the real transmitters and just alter the real frequency a small amount.   That sounds very very easily possible.   

All they have to do is rebroadcast the very weak satellite signals at a stronger signal than received from the real transmitters and just alter the real frequency a small amount.   That sounds very very easily possible.

These things often do when academics are making a splash.  However there still has never been a confirmed case of it being used "in the wild" - so it can't be that easy.  Remember they didn't do this remotely, but sat on the yacht with their equipment.

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

You can triangulate a cell phone by getting signal strengths from multiple towers in known locations.   Police have used this to track people and locate cell phones,  it works even when the phone is not being used,  it just has to be powered up.   The cell hand-off software gets signal strengths from towers and registers with the one that has the best signal quality.  The positional accuracy is fairly low,  depending on the number of towers. and the terrain.    That system doesn't use GPS or wifi at all.   But it only works where there is good cell phone coverage.  GPS still works out in the middle of nowhere where there are no towers and no cell phone coverage.

I've used GPS on a flight between Sydney and Honolulu.  Somewhere over mid pacific.   No land based towers.   

Quote from: Aliveandkicking on May 11, 2015, 05:23:18 AM

All they have to do is rebroadcast the very weak satellite signals at a stronger signal than received from the real transmitters and just alter the real frequency a small amount.   That sounds very very easily possible.

These things often do when academics are making a splash.  However there still has never been a confirmed case of it being used "in the wild" - so it can't be that easy.  Remember they didn't do this remotely, but sat on the yacht with their equipment.

You are making it sound hard. If you just relay the existing signals you will profoundly alter the accuracy of all those receivers who lock onto the relay transmitter even if they are hundreds of miles from the relay.     

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

Make and model please.

Quote from: Rayzor on May 10, 2015, 07:46:05 PM

Quote from: jroa on May 10, 2015, 07:25:30 PM

Actually, a line of sight signal does need relays if the receiver is not in the line of sight.  To use your own words, Duh.

True for some things like voice or data,  but not true for GPS,  GPS relies on the precise time difference of signals from different transmitters to triangulate the reciever position.  So GPS will ONLY work when there is a direct line of sight between transmitters and receivers.    GPS won't work through a relay.

The GPS system would not work without satellites.

You know can  you things make up your mind . Your satalite is either fix stationary or wizzing around earth at 25,200 kmh. So which is it ?

Learn about satellite orbits.

Quote from: jroa on May 11, 2015, 05:06:55 AM

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

Make and model please.

Do you have to come in with these shit one liners?

Quote from: inquisitive on May 11, 2015, 02:57:04 PM

Quote from: jroa on May 11, 2015, 05:06:55 AM

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

Make and model please.

Do you have to come in with these shit one liners?

Seems like a reasonable question to me.  Are current cell phone towers really transmitting their geographical location and are current cell phone chips really using speed of light calculations? or is it instead just a gps chip on board?  I have no idea.  Googling is not giving me a good answer so far

After 20 minutes of trying i cannot see any evidence current phones are using anything other than true GPS plus an assisted location method for greater accuracy

Quote from: JimmyTheCrab on May 12, 2015, 02:27:36 AM

Quote from: inquisitive on May 11, 2015, 02:57:04 PM

Quote from: jroa on May 11, 2015, 05:06:55 AM

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

Make and model please.

Do you have to come in with these shit one liners?

Seems like a reasonable question to me.

Ah, it's just all he ever does - never any proper debate.

Are current cell phone towers really transmitting their geographical location and are current cell phone chips really using speed of light calculations? or is it instead just a gps chip on board?  I have no idea.  Googling is not giving me a good answer so far

After 20 minutes of trying i cannot see any evidence current phones are using anything other than true GPS plus an assisted location method for greater accuracy

It's all based on a geolocation API.  If you have a good GPS signal, then it will of course use that.  If it doesn't then it falls back onto cell tower triangulation, IP location the WiFi node lookup database.  At least that's how the Google API works anyway.

Quote from: Aliveandkicking on May 12, 2015, 02:49:14 AM

Quote from: JimmyTheCrab on May 12, 2015, 02:27:36 AM

Quote from: inquisitive on May 11, 2015, 02:57:04 PM

Quote from: jroa on May 11, 2015, 05:06:55 AM

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

Make and model please.

Do you have to come in with these shit one liners?

Seems like a reasonable question to me.

Ah, it's just all he ever does - never any proper debate.

Quote

Are current cell phone towers really transmitting their geographical location and are current cell phone chips really using speed of light calculations? or is it instead just a gps chip on board?  I have no idea.  Googling is not giving me a good answer so far

After 20 minutes of trying i cannot see any evidence current phones are using anything other than true GPS plus an assisted location method for greater accuracy

It's all based on a geolocation API.  If you have a good GPS signal, then it will of course use that.  If it doesn't then it falls back onto cell tower triangulation, IP location the WiFi node lookup database.  At least that's how the Google API works anyway.

How about you give the make and model so we can find out how it works rather than speculating?

Quote from: jroa on May 11, 2015, 05:06:55 AM

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

You can triangulate a cell phone by getting signal strengths from multiple towers in known locations.   Police have used this to track people and locate cell phones,  it works even when the phone is not being used,  it just has to be powered up.   The cell hand-off software gets signal strengths from towers and registers with the one that has the best signal quality.  The positional accuracy is fairly low,  depending on the number of towers. and the terrain.    That system doesn't use GPS or wifi at all.   But it only works where there is good cell phone coverage.  GPS still works out in the middle of nowhere where there are no towers and no cell phone coverage.

I've used GPS on a flight between Sydney and Honolulu.  Somewhere over mid pacific.   No land based towers.

That's funny, my last plane trip I couldn't use my Garmin GPS or phone GPS. As soon as I got on the plane both GPS units showed me in BWI airport until I got off of the lane in Florida.

Quote from: JimmyTheCrab on May 12, 2015, 04:30:28 AM

Quote from: Aliveandkicking on May 12, 2015, 02:49:14 AM

Quote from: JimmyTheCrab on May 12, 2015, 02:27:36 AM

Quote from: inquisitive on May 11, 2015, 02:57:04 PM

Quote from: jroa on May 11, 2015, 05:06:55 AM

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

Make and model please.

Do you have to come in with these shit one liners?

Seems like a reasonable question to me.

Ah, it's just all he ever does - never any proper debate.

Quote

Are current cell phone towers really transmitting their geographical location and are current cell phone chips really using speed of light calculations? or is it instead just a gps chip on board?  I have no idea.  Googling is not giving me a good answer so far

After 20 minutes of trying i cannot see any evidence current phones are using anything other than true GPS plus an assisted location method for greater accuracy

It's all based on a geolocation API.  If you have a good GPS signal, then it will of course use that.  If it doesn't then it falls back onto cell tower triangulation, IP location the WiFi node lookup database.  At least that's how the Google API works anyway.

How about you give the make and model so we can find out how it works rather than speculating?

Make and model of what? (hint: I'm not jroa). What was speculative about my post?  I was describing the Google Geolocation API, rather than making claims for any specific hardware.

The make and model isn't going to tell you very much anyway - different apps could potentially hook into different geolocation API, or use it in different ways.  Here's how the Google one works:

https://developers.google.com/maps/documentation/business/geolocation/

The Google Maps Geolocation API returns a location and accuracy radius based on information about cell towers and WiFi nodes that the mobile client can detect.

I've messed around with it myself - it's very easy to hook up.

Quote from: Rayzor on May 11, 2015, 07:05:40 AM

I've used GPS on a flight between Sydney and Honolulu.  Somewhere over mid pacific.   No land based towers.

That's funny, my last plane trip I couldn't use my Garmin GPS or phone GPS. As soon as I got on the plane both GPS units showed me in BWI airport until I got off of the lane in Florida.

You need a window seat and hold it against the window, otherwise the plane fuselage shields it.   It was the Garmin Nuvi I use in the car,   and  I managed to get the trip max speed set to 750 something kph.   I haven't tried it with the phone.   I'm not sure if gps still works in flight mode.

Quote from: Aliveandkicking on May 12, 2015, 05:16:00 AM

Quote from: JimmyTheCrab on May 12, 2015, 04:30:28 AM

Quote from: Aliveandkicking on May 12, 2015, 02:49:14 AM

Quote from: JimmyTheCrab on May 12, 2015, 02:27:36 AM

Quote from: inquisitive on May 11, 2015, 02:57:04 PM

Quote from: jroa on May 11, 2015, 05:06:55 AM

Quote from: JimmyTheCrab on May 11, 2015, 04:53:51 AM

Loran couldn't tell you your altitude either....as it was ground based.

Anyway, it's been turned off now because....satellites!

My cell phone uses ground based technology and can tell me not only my altitude, but get this, my position as well. 

Make and model please.

Do you have to come in with these shit one liners?

Seems like a reasonable question to me.

Ah, it's just all he ever does - never any proper debate.

Quote

Are current cell phone towers really transmitting their geographical location and are current cell phone chips really using speed of light calculations? or is it instead just a gps chip on board?  I have no idea.  Googling is not giving me a good answer so far

After 20 minutes of trying i cannot see any evidence current phones are using anything other than true GPS plus an assisted location method for greater accuracy

It's all based on a geolocation API.  If you have a good GPS signal, then it will of course use that.  If it doesn't then it falls back onto cell tower triangulation, IP location the WiFi node lookup database.  At least that's how the Google API works anyway.

How about you give the make and model so we can find out how it works rather than speculating?

Make and model of what? (hint: I'm not jroa). What was speculative about my post?  I was describing the Google Geolocation API, rather than making claims for any specific hardware.

The make and model isn't going to tell you very much anyway - different apps could potentially hook into different geolocation API, or use it in different ways.  Here's how the Google one works:

https://developers.google.com/maps/documentation/business/geolocation/

Quote

The Google Maps Geolocation API returns a location and accuracy radius based on information about cell towers and WiFi nodes that the mobile client can detect.

I've messed around with it myself - it's very easy to hook up.

I got mixed up with you an Jroa because you answered inquisitive with the 'shit one liner' answer.

How accurate a position can you get from the google API? sufficient to navigate a car in a city?   I am assuming the answer is no going by everything i read earlier and my understanding of the technical difficulties involved - signals would be bouncing off everything in sight

Anyway since it is not your phone in question it is not much of a big deal.

I got mixed up with you an Jroa

The horror....the horror...

How accurate a position can you get from the google API? sufficient to navigate a car in a city?   I am assuming the answer is no going by everything i read earlier and my understanding of the technical difficulties involved - signals would be bouncing off everything in sight

I think you are correct - however I believe they are increasingly sophisticated about inferring a location from numerous data sources if GPS is not available.  The latest iPhone will:

Depending on your device and available services, Location Services uses a combination of cellular, Wi-Fi, Bluetooth, and GPS to determine your location. If you're not within a clear line of sight to GPS satellites, your device can determine your location using crowd-sourced Wi-Fi5 and cell tower locations or iBeacons.

My original point, however, is that ground based location services couldn't work out your altitude.  However jroa said his phone could, and I was just pointing out that all his phone was doing was going to a database of wifi nodes and working out where he was from whichever nodes he was in range of.   When I've tested it in London, I find it's pretty inaccurate for altitude.  And of course this method won't work at all up in the mountains - something jroa knows, but he likes to play dumb.

Meanwhile, GPS is used for timing and positioning at high accuracy across the world.

Yes a device can acquire a position without GPS, such as the cheaper version iPad that is not GPS equipped.
It can use wifi or cellular triangulation.
The elevation is typically gained by looking at a digital topographic map data once your location is determined
(behind the scenes).

These devices cannot tell you your speed over ground, that requires a satellite.
The same non-GPS equipped iPad will report other data with a zero value for speed.
You can try this is you have a non-cellular equipped iPad (the GPS hardware is also in the cellular module).
Get a speedometer App, and it won’t work. what!!! no doppler shift

Signal from a satellite is useless once propagated. The reason is that if a signal path is not direct,
the receiver can’t know the timing data is accurate. It would be impossible for the transmitter or receiver
to compensate for delay if the signal path is not known. That’s the whole idea behind GPS.

It’s quite ridiculous to not believe satellites exist. Far more ridiculous than the whole flat Earth thing.
Since it can be so easily demonstrated that a TV signal is actually arriving from a fixed point in the sky for prolonged period.

Yes a device can acquire a position without GPS, such as the cheaper version iPad that is not GPS equipped.
It can use wifi or cellular triangulation.
The elevation is typically gained by looking at a digital topographic map data once your location is determined
(behind the scenes).

These devices cannot tell you your speed over ground, that requires a satellite.

If you know your position and your immediately previous position then you can estimate your speed.   The fact you cannot estimate your speed without GPS shows the non-GPS cell phone triangulation/wireless method to estimate position is clumsy, slow and very significantly unreliable at position finding.

GPS Doppler shift measurement is not essential to determine an estimation of speed.  Doppler shift just makes it far more accurate and is a relatively instantaneous estimation compared to using way points and then estimating what can only be an historically based speed rather than a true current speed.

However, I have to say it is very interesting that GPS enables speed estimation using only the estimations involved to determine  a single position using the Doppler method!     I think i can justify saying my mind is being blown by that thought