[Milkman]

I hadn't noticed before but my niece was riding with me the other day and said that the NAV was behind where we actually are at. I thought it was just a hiccup. But, today I noticed it at a stop light. The arrow was a good half block behind the intersection and I was at the red light. Is this a flaw or should I have the dealer check it out?

 

[generator]

You can fine-tune the navigation. I have done it by mistake. You basically have to find a reliable intersection, then zoom in, and move the cursor to your exact position and set that as the offset. I don't remember how to get into the setup mode though. You may have to look through the users manual.

For instance when the cars are first delivered and you turn them on the nav shows the car to be somewhere on the west coast even if you are parked in New York. The dealer adjusts this of corse. I beleive Jaak has a post up here that shows how to get into the special mode. I did it one day goofing around and I watched in humor as I drove thru California on my screen but was really in Manhattan. It took a while for me to reset it though. I had to drag the cursor from the west coast to the east coast and then zoom in to my block. Was not so funny anymore as I spent 15 minutes zooming in and out.

 

[dklanecky1]

Is your NAV signal indicator showing green or yellow when your not shown in the right location?

I seem to recall that if it's yellow, the NAV system just guess-estimates your position based on the last good signal it had and your speed and heading prior to loss of the trianglulation signal.

Mine occasionally goes yellow and loses my exact position, but it always corrects as soon as the signal triangulates again.

I also don't drive in an area with a lot of obstructions like tall buildings etc. so I can imagine that if you did, you could be indicated "in the wrong place" a lot.

 

[EasternPA]

Very true with the tall buildings. I commute to, and stay in, Manhattan every week and the Nav is the worst in there. Thank god I know where I'm going. Since street navigation-oriented gps systems all have to do a little fudging to try to figure out where you really are, my position jumps all over the place, sometimes even sitting at a red light. My car marker will jump a block ahead or back, or suddenly change from an east-west street to a block or two up, but now on a north-south avenue.. forget about trying to follow directions to a destination. I really feel for people who NEED the gps in the city, cuz it ain't happenin'.

The same happened with my Garmin, too, so its not just ours. Surroundings have a lot to do with it.

 

[jaak]

Not only do buildings block the signals from the satellites (depending where they are) but the signal can then arrive at the receiver as a reflection off some of the buildings. Especially the ones with metallized windows (mirrored). Since GPS is timing based, this creates a longer signal path and the signal gets to the receiver late. Of course, this means it's wrong and depending on how many other satellites it "sees" could screw up the calculation of where you are.

This should average out when you're moving and is most likely the worst when going slow or stopped.

Hey, nothing's perfect. You should try XM or Sirius without local repeaters in a downtown core. e.g. Toronto. It's almost hopeless!