Standby for the apocalypse!

#61
More to the point, how do members of the constellation calculate and correct their position? I seem to recall ground stations being used as a reference.
Nah - that's DGPS with ground stations; they have their antennae at precisely surveyed points and then the system compares the received position from the satellites with the known position of the antenna and generates an XY and Z correction offset, which is transmitted encrypted (so you have to pay a subscription for the decode keyin order to usue it) and then received by the DGPS receiver (such as on a - ooooh - let's say a survey ship), which then applies the correction to it's own received GPS position. Typically we'll rock three receivers and receive corrections from three or four ground stations spread around a circle around our work area, with the three positions being fed into the nav software, which then'll mean out the three to one rather precise position.

You don't actually triangulate using signals sent to and from the satellites, or "track" them. All the SVs do is transmit, at a lowly 50W, a time signal, an almanac and ephemeris data. In other words, all the SVs do is say, "At this time on this date I will be at this point in the sky and this high above the spheroid." The receiver does all the work, using trilateration, to determine your position from ranges and bearings; essentially a GPS satellite is a transmitter that sends out a big-ass look-up table of numbers - which is why you want a nice spread of seven to nine SVs around you to get a decently accurate fix.

It's a myth that "GPS can be used to track you." GPS receivers do just that - receive. The transmitter in your 'phone, however, can be used by software to broadcast your position once it has got it from the built in GPS receiver.

And here endeth the lesson.
 
#62
Correct, but there has to be a reference to which they can refer to transmit that data accurately. DGPS reference to ground stations to finely correct data locally as you've said, but what about orbital drift? To what do they reference and correct the constellation to give an accurate ground picture?

I think they're running caesium clocks on board and drift is measured by ground stations and updated but is there any positional correction or is the drift updated in the on board database?
 
#63
Correct, but there has to be a reference to which they can refer to transmit that data accurately. DGPS reference to ground stations to finely correct data locally as you've said, but what about orbital drift? To what do they reference and correct the constellation to give an accurate ground picture?

I think they're running caesium clocks on board and drift is measured by ground stations and updated but is there any positional correction or is the drift updated in the on board database?
Small thrusters onboard each SV for course correction, apparently.

Fill yer boots:-

Garmin | What is GPS?
 
#65
It's a myth that "GPS can be used to track you." GPS receivers do just that - receive. The transmitter in your 'phone, however, can be used by software to broadcast your position once it has got it from the built in GPS receiver.

And here endeth the lesson.
It's worse than that, with the phone hacked you can switch on a phone remotely, and then get it to transmit it's location. You need to take the sim and battery out to stopped worrying about it leaking your position

The fact the GPS isn't transmitting your position, would be no consolation to someone being monitored

I'm not talking security services either, plenty of legal or black market ways to do it
 
#66
It's worse than that, with the phone hacked you can switch on a phone remotely, and then get it to transmit it's location. You need to take the sim and battery out to stopped worrying about it leaking your position

The fact the GPS isn't transmitting your position, would be no consolation to someone being monitored

I'm not talking security services either, plenty of legal or black market ways to do it
There are very few smart phones with user removable batteries now. Most of those that do tend to be more basic these days. Users "want" style, unibody construction and water resistance rather than user replaceable batteries. They tend to replace the phones every couple of years anyway...
 
#67
There are very few smart phones with user removable batteries now. Most of those that do tend to be more basic these days. Users "want" style, unibody construction and water resistance rather than user replaceable batteries. They tend to replace the phones every couple of years anyway...
Hmm I wonder why the market has gone that way, but then I'm still not convinced Facebook wasn't really a cover for a clever covert spying operation
 
#69
It's worse than that, with the phone hacked you can switch on a phone remotely, and then get it to transmit it's location. You need to take the sim and battery out to stopped worrying about it leaking your position

The fact the GPS isn't transmitting your position, would be no consolation to someone being monitored

I'm not talking security services either, plenty of legal or black market ways to do it
Indeed. So where exactly am I right now, then...?
 
#70
How do they correct for depth?
We build a tidal model using some other software, either predicted or observed, and derive corrections based on the specified datum (LAT or MSL usually) then apply them in processing. Simples...
 
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#71
I wonder why the market has gone that way
Possibly because of the move to lithium polymer batteries, which are a bit tasty and it's probably been deemed that they're not safe to be fiddled with by chavs, the educationally-deficient and other lower social orders.
 
#75
Nah - that's DGPS with ground stations; they have their antennae at precisely surveyed points and then the system compares the received position from the satellites with the known position of the antenna and generates an XY and Z correction offset, which is transmitted encrypted (so you have to pay a subscription for the decode keyin order to usue it) and then received by the DGPS receiver (such as on a - ooooh - let's say a survey ship), which then applies the correction to it's own received GPS position. Typically we'll rock three receivers and receive corrections from three or four ground stations spread around a circle around our work area, with the three positions being fed into the nav software, which then'll mean out the three to one rather precise position.

You don't actually triangulate using signals sent to and from the satellites, or "track" them. All the SVs do is transmit, at a lowly 50W, a time signal, an almanac and ephemeris data. In other words, all the SVs do is say, "At this time on this date I will be at this point in the sky and this high above the spheroid." The receiver does all the work, using trilateration, to determine your position from ranges and bearings; essentially a GPS satellite is a transmitter that sends out a big-ass look-up table of numbers - which is why you want a nice spread of seven to nine SVs around you to get a decently accurate fix.

It's a myth that "GPS can be used to track you." GPS receivers do just that - receive. The transmitter in your 'phone, however, can be used by software to broadcast your position once it has got it from the built in GPS receiver.

And here endeth the lesson.
A updated version of LORAN C [yes I'm old and a little out of date]
 
#76
OMEGA. Don't get me started. Wrote ATP electronics/nav aids and saw it was still in the syllabus despite the last station being dismantled a couple of years previously. Decided to ignore and studied everything else.

Sure as shit, I failed by one or two percent due to questions on OMEGA in the exam. Cornered the old fart who set the exams and asked him about it, to be told it was in the syllabus so get on with it.

Fuck!

Only allowed to rewrite in four weeks (unlike the dumbed down version these days with unlimited rewrites whenever you feel the urge) so went home and burned the midnight oil. Wrote again and damned near crapped myself when the result came up and I saw the two zeros. Took me a couple of seconds of sheer panic (it was my last allowed rewrite before having to do the entire lot over) before I spotted the word 'Passed' and the 1 before the zeros.

Still took a few minutes to convince my arse to let go of the seat cushion...
 
#79
They will blame it on global warming, and the only solution is to go vegan, and then they'll put a tax on meat products and create meat credits for farmers to create another tax
And ban wood burners , because as we know processed fuels are so cheap these days , but don't for **** sake , switch off all the heating and wear a fleecy because that puts microfibres in the water and kills all the fish .
 

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