: Calibration of GPS map



jgrade
07-03-08, 10:35 AM
Every time I try to calibrate my GPS to position the pointer on the screen accurately, it always resets and is ALWAYS off. If I get to an intersection or cross road, the nav shows that I am still a little bit away and not actually where I am supposed to be. When I have a chance, like at a red light, I calibrate the nav so that I am dead center of the intersection. The correction holds for a few minutes, then it goes out of whack again.

It is off enough that I have missed streets because they were close together, in reality, but the nav showed I was no where (relatively speaking) close to the turn.

Any ideas on how to make the corrections stick?

pjbizjak
07-03-08, 12:53 PM
Have you tried ejecting the nav disc then reinserting it?

jgrade
07-03-08, 01:39 PM
Only by accident, but I will try again.

bigdog9586
07-04-08, 06:08 PM
I have a aftermarket GPS in another vehicle and at its best it shows that it is with in 34 feet of dead center so to speak but sometimes gets worse as it runs into trees or other obsticals that block out a sat. So you may be as good as it gets.

Lifer
07-05-08, 05:23 PM
When GPS was first introduced by the Dept of Defense (NAVSTAR-GPS) it was then designed as accurate to +- 10 meters for the military and +- 100 meters for the civilian market (begining in 1983). GPS includes a (currently disabled) feature called Selective Availability (SA) that can introduce intentional, slowly changing random errors of up to a hundred meters (328 ft) into the publicly available navigation signals. This signal was finally discontinued in 2007. Now, due to a number of factors, the civilian version is good to +- 15 meters on a good day.

Load your Google for more information.

jgrade
07-07-08, 10:08 AM
Then the question is does anyone else show the same issue? I have an 06' with OEM nav. Also, is this not what the calibration is supposed to fix? The wife has a new GMC Acadia and the nav is dead on no matter the zoom. I just chalk it up to another annoyance of the STS line.

pjbizjak
07-07-08, 10:33 AM
Have you looked into getting the most recent version disc?

AllWheelEric
07-07-08, 11:54 AM
Then the question is does anyone else show the same issue? I have an 06' with OEM nav. Also, is this not what the calibration is supposed to fix? The wife has a new GMC Acadia and the nav is dead on no matter the zoom. I just chalk it up to another annoyance of the STS line.

No, I do not have this issue.

I don't think this is what calibration is supposed to fix. I'm guessing, but I think it just tells the car to forget what it had previously memorized about where the car was and which way it was pointing. The car uses other sensors as backup to the GPS receiver, so you still have a moving map in a tunnel, or under heavy tree cover, etc.

It's hard to guess how the GPS would be off so often. Is it consistent, e.g., are you always shown as west of true location? I wonder if the map data is incorrect in your area. Is your GPS reception OK? If it weren't, there would be a GPS icon with a slash through it on the left side of the screen. I have also heard that the government can reactivate "Selective availability" for limited geographic areas. Are you driving near a military base or Area 51?

Anyway, it's not normal so I would suggest trying to get the dealer to fix it.

jgrade
07-07-08, 03:08 PM
pjbizjak: I have the most recent version of the disc.

AllWheelEricL: I have not noticed if the problem is created when heading in a particlular direction. I need to pay attention to that and report back. Truthfully, I hardly use the map since my BT will not mute and I sit on the source screen so I can pause the CD to be able to answer the phone. I'm sick to death with the dealer and would rather live with the problem then take it back yet again. I am in a suburb just north of Chicago, so I hope the data is accurate. Basically I notice the issue when stopped at an intersection. The pointer is always about a 1/4 inch away from the actual location.

One thing I will try is changing the zoom and see if it helps.

Thanks for all who replied. I appreciate the assistance.