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does GPS need a subscription with the provider? I heard that it works directly from the satellite, but how can you name an address and see the location?
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Posted: 2004-09-22 10:28:53
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GPS works directly from satalites in space to triangulate your exact place on earth. It does not need a subscription to a service. GPS receivers need to talk to at least 3 satelites to get a fix on you and tell you where you are on your reciever.
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Posted: 2004-09-22 10:33:22
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yeah, there are 66 low orbitin satellites that do the work.
and did u know that commercially available gps systems do not show the exact location. they have an inbuilt error on the locaction. its off by a few meters.
this is to prevent terrorists from using gps devices to target buildings.
only the us military have the real co ordinates!!
but i hear the eu is coming up with its own gps network which is leading to a lot of diplomatic troubles. russia has one up and running too.
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Posted: 2004-09-22 11:32:08
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Another conspiracy!
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Posted: 2004-09-22 11:53:00
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i think it's wrong. The US military has not been able to do any real 'precise bombing' so they've probably been given wrong coordinates just like the rest of us stupid sods
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Posted: 2004-09-22 11:56:53
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It is true that the US military has access to their own GPS system which is a lot more accurate than the system available to us general public.
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Posted: 2004-09-22 12:15:03
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ok, now the satellite does all the work and it has nothing to do with the provider.. but how the satellite knows the name of every single city in every country? I mean im in Bahrain for sure you will not even find the name of cities and villages even in a Map
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Posted: 2004-09-22 12:36:18
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oh.. the gis mapping is done earlier using remote sensing satellites. which records the physical co ordinates and elevation and stores it on huge mainframe computers.
vlam.. lol
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Posted: 2004-09-22 12:53:12
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GPS is subscription-free but satellites only provide co-ordinates, not place names or addresses.
To get these you need a device that holds maps and can translate the co-ordinates into a position on a map. You need to pay for these maps.
If your cell provider offers this service, then your device communicates its position, sometimes by GPS or more often by triangulating signal strength from cell masts, to your provider. Your provider decodes the position and sends back the address.
[ This Message was edited by: duncanb99 on 2004-09-22 12:01 ]
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Posted: 2004-09-22 12:59:01
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The signals received up by the commercially available GPS systems are picked up from 27 US Military satellites. I believe these were launched in the very early 1980's, but it wasn't until 2000 that President Clinton had the deliberate "selective availability" turned off. This meant that the scrambling of the signal for commercial users was no longer used - increasing accuracy significantly.
The inaccuracy of a few metres that still exists is due to atmospheric interference. The military largely get around this using a 2nd signal that commercial units don't currently receive.
The only info that a receiver can derive from the satellites is a 3D position, so it's up to the receiver to interpret that using it's own mapping software/database.
The big disadvantage of GPS use in mobile devices is that the signal from the satellites is pretty weak and is significantly blocked by most solid objects (including tree canopies and walls/ceilings). Use indoors is rarely possible and even using in a city with skyscrapers around is difficult, as a GPS receiver needs timing signals from at least 3 satellites at any given time.
I believe it's this that has prevented GPS incorporation into phones becoming widespread. That, plus the fact that it generally takes a couple of minutes to acquire a position from a "cold start", compared to the few seconds that positioning via timing & signal strength of a GSM/GPRS network takes (although obviously much less accurate).
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Posted: 2004-09-23 01:08:54
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