[Jongi]

Can anyone direct me to some literature that explains how the technology works?

How it is that the GPS will know how to connect your current position to the destination co-ordinates using the roads that are mapped?

[E90Fleet]

Do you want to know how GPS knows where you ae or just how it knows it must follow the roads ?

The roads bit is easy, the computer is programmed to only stay within the lines of the programmed roads. The roads programme is very large, thats why it has to be on a DVD. The Nav computer is also pretty powerfull and has its own programming onboard.

These arnt simple programmes, but very complex ones. Thats why a new nav DVD costs around R3,000

The company Navtec makes the roadmap data for BMW and a few other manufacturers

[poldim]

Originally Posted by Jongi

Can anyone direct me to some literature that explains how the technology works?

How it is that the GPS will know how to connect your current position to the destination co-ordinates using the roads that are mapped?

http://electronics.howstuffworks.com/gps.htm


Using the sats, your car gets its lat. and lon. location, then your gps software has roads mapped out according to their lat and lon. The direction of travel, speed, etc. is calculated from the difference of location over a time interval. The more sats you pic up, the more accurate your signal is.

[maq]

In Europe they call it Sat Nav, which I think is a better term. Your car constantly sends signals to a satellite, which uses the signals locate your position. The satellite then sends signals back to your car, to tell the vehicle your current position. That's the "sat (as in satellite)" part. Using a pre-installed map that is stored in your car's computer, it can locate you on the map as in real life and give you directions. That's the "nav (as in navigation)" part. The newer systems can give you live traffic/road condition information too.

[poldim]

Originally Posted by maq

In Europe they call it Sat Nav, which I think is a better term. Your car constantly sends signals to a satellite, which uses the signals locate your position. The satellite then sends signals back to your car, to tell the vehicle your current position. That's the "sat (as in satellite)" part. Using a pre-installed map that is stored in your car's computer, it can locate you on the map as in real life and give you directions. That's the "nav (as in navigation)" part. The newer systems can give you live traffic/road condition information too.

As far as I know you dont send anything. You dont have a nav sender, all you have is a receiver. The sats are constantly sending out signals, and your car calculates how long it takes the signal to reach it and using 3 sats it triangulates its position.

[E90Fleet]

Your car only recieves signals, it does not transmit anything.

[fideba]

I actually wrote some GPS software a while ago, so please let it be clear: there is no way you send anything to the satelites. You just receive signals from one or more satelites, and based on that, your position is determined.
Theoretically, you need two satelites to determine your position, and a third for your altitude. In practice, the more satelites, the better (although if you have as of 6 different signals, some GPS soft will ignore the other ones to speed up calculations).
Then this position is mapped on the maps that are on your DVD. I don't think the nav software is on the DVD, I suppose only the maps are.
The nav software will then try to determine the fastest way to get to your destination. Mind that this requires a lot of calculation power. That's why when you miss a turn, the system won't always show you the best way to continue. Most nav systems will first try to route you back to the initial chosen route, because it's easier (read: faster) to calculate this, then start over and try to find a complete new route. If you deviate enough from the initial path, the system will start recalculating (mind: in the BMW system, I find the recalculation very fast. Well, I guess it's expensive enough :-)

If you want more (basic) info: check out GPS Navigation for Dummies !
http://www.amazon.com/gp/product/076...lance&n=283155

[LEDZEP]

Originally Posted by poldim

http://electronics.howstuffworks.com/gps.htm


Using the sats, your car gets its lat. and lon. location, then your gps software has roads mapped out according to their lat and lon. The direction of travel, speed, etc. is calculated from the difference of location over a time interval. The more sats you pic up, the more accurate your signal is.

I was just about to post the same link!

[lungdoctor]

Can we find a way to track our own cars on our home pc- BMW assist can tell the car is at all times, is software available for home use?

[bimmer4me]

1) BMW Assist can NOT tell where the car is at all times. Only when the BMW Assist call is initiated. Why? I have no idea.

2) There are GPS devices available that you can stick inside the car, underneath the car or even inside the bumper. Some run on batteries and some hook up to the car's power. You can then later remove the device and hook it up to your PC and it will show you EXACTLY where the car was and at what time. It's like TiVo for a Nav system. I know a little bit about because a friend of mine used it to track his wife to help find out about some "extra activities".

[- Paul -]

http://en.wikipedia.org/wiki/Gps

More than you'd probably want to know!

[E90Fleet]

The way BMW USA Assist track a car with nav is:

When they call is activated the nav computer in your car sends its current position over the connection to the BMW Assist call centre and updates it while you drive

[bimmer4me]

Originally Posted by E90Fleet

The way BMW USA Assist track a car with nav is:

When they call is activated the nav computer in your car sends its current position over the connection to the BMW Assist call centre and updates it while you drive

I feel very uncomfortable contradicting Sir E90Fleet, however, the first time I used BMW Assist they told me that they only know the location of the car when the call is placed to BMW Assist. I was trying to get to a location and I asked them to stay on the phone with me so they could guide to my destination. The BMW Assist person specifically said they only know my location when the call is received and is not updated while driving so I had to tell him verbally where I was.

[E90Fleet]

Originally Posted by bimmer4me

I feel very uncomfortable contradicting Sir E90Fleet, however, the first time I used BMW Assist they told me that they only know the location of the car when the call is placed to BMW Assist. I was trying to get to a location and I asked them to stay on the phone with me so they could guide to my destination. The BMW Assist person specifically said they only know my location when the call is received and is not updated while driving so I had to tell him verbally where I was.

Ok, we dont have that service here, so Im no expert on it.
Now I know its not continually updated

Thanks

[rag21]

Originally Posted by Jongi

How it is that the GPS will know how to connect your current position to the destination co-ordinates using the roads that are mapped?

MAGIC

[maq]

Thanks for the correction guys.

[poldim]

np

[voltron1011]

Another interesting tidbit:
The US government actualy ownes all 24 GPS satelites that are in orbit. The technology was initially used to help Tomohawk cruise-missles find their targets and the military only had GPS receivers. They finally released it to the civilian market but the civilian recievers are less sensitive than the military one's. If a war were to ever break out, the military can actually turn up the errors on the GPS satelites so that only the US military recievers will operate. All of the other off-the-shelf GPS recievers will be useless at that point.

[kal-el]

Originally Posted by voltron1011

Another interesting tidbit:
The US government actualy ownes all 24 GPS satelites that are in orbit. The technology was initially used to help Tomohawk cruise-missles find their targets and the military only had GPS receivers. They finally released it to the civilian market but the civilian recievers are less sensitive than the military one's. If a war were to ever break out, the military can actually turn up the errors on the GPS satelites so that only the US military recievers will operate. All of the other off-the-shelf GPS recievers will be useless at that point.

very interesting......

[poldim]

Originally Posted by voltron1011

Another interesting tidbit:
The US government actualy ownes all 24 GPS satelites that are in orbit. The technology was initially used to help Tomohawk cruise-missles find their targets and the military only had GPS receivers. They finally released it to the civilian market but the civilian recievers are less sensitive than the military one's. If a war were to ever break out, the military can actually turn up the errors on the GPS satelites so that only the US military recievers will operate. All of the other off-the-shelf GPS recievers will be useless at that point.

I remember reading that the military actually uses another signal similar to GPS but different. Its more accurate and more secure. I'll see if I can remember what its called...

[rprasad]

IIRC, the commericial resolution is as good as the military resolution these days. I think the Pentagon opened up the higher res military-only signal for commerical use. Something like a 1 meter accuracy.

[mowog]

Originally Posted by bimmer4me

The BMW Assist person specifically said they only know my location when the call is received and is not updated while driving so I had to tell him verbally where I was.

I'm only guessing here, but I'd say this might have something to do with the car's position being triangulated by the cellular network, and this location being transmitted to BMW Assist when they take your call.

IIRC US cellular networks have mandated handset location resolution for emergency calls, and I know that Australian networks are able to triangulate your location, but it's only done during actual emergencies.

I think if you have the BMW Online service activated the car will establish a GPRS connection and upload more data to BMW.. but I've never used it so I don't know if that includes location information.

--m