App charts police officer movements

[Alarm]

Another way of looking at this is the non geostationary sats ( hope i can call them sats) which orbit the earth twice for every rotation of the earth could not possibly know the "ident" of every device looking for the signals needed. Can you imagine the computing power needed on each for this? You would need 24 orbital earth stations to house the processing power needed even with terabyte drives or solid state as the higher platform is now.
So you see this is why they are passive, it also keeps the costs down.

 

[Paul_C]

a service. What is the first thing a Satnav says when you switch it on? Aquiring signal. How do they do that? magic? witchcraft? No it's by pinging.

No it isn't. "Acquiring signal" means that the receiver you have just switched on is simply checking which satellite signals can be received at its present location, then it can calculate where it is on the globe.

HOW does a satellite know a device exists?

It doesn't know. It doesn't need to know. It's just sending out a signal which can be received by any and all GPS receivers on the ground anywhere within its range.

HOW does a device tell a satellite know it exists?

The GPS receiver doesn't tell any satellite that it exists. It is only receiving signals, not transmitting.

I wouldn't have thought this is a difficult concept to understand.

Take a lighthouse as a much simpler example. Does a ship at sea send some sort of light signal toward land so that the lighthouse can then flash back to give its location? No. The lighthouse is continuously sending out its sequence of flashes and neither knows nor cares whether there is one ship or a whole flotilla of ships seeing them. Anyone on a ship can simply scan along the coastline looking for lighthouses within visible range and then work out which lighthouse is which from the different flash sequence. The light signals in this case are one way, from lighthouse to ship. Just as GPS signals are one way, from satellite to SatNav receiver.

 

[vokera80e]

ive a better idea. CCTV is paid for by us the tax payer,why not bring it into the public domain. i read recently that some towns and cities are going to get their own tv channel, so if it's piped into your televisions you could stop up all night and watch all the scum bags doing their thieving,mugging,etc ... and see if any coppers are on the beat. even the next day keep an eye on all the traffic jams and then make decision what route to take..( dream on )

 

[expertgasman]

The device doesn't know that a satellite doesn't exist....hence ping. How incoherent are people? If you have a mobile phone...how can it communicate to a satellite? The sat pings, then gets a ping back? Are people really that stupid? How does a sat lock on to a device?

I'm nackered after reading all that!! , and I wasn't doing it at 2.30 am. Micky : Have you got it yet? It is fairly simple and the icing on the cake is the TomTom Q&A