I've seen my GPS get screwed up a few times (i.e. showing me as being a block or so away from where I actually am). On one trip down the 405, it was especially painful since it kept thinking that I was off the freeway and encouraging me to get on...
I don't know how to reproduce the problem. I haven't noticed it happen when I just have the map on, but have seen it happen a number of times when a destination is programmed. I don't program in destinations all that often...
I have a Dension 500... I'm a bit concerned that
Porsche
would use this as a cop-out (unless of course it somehow could effect the GPS -> NAV communication...)...
I have a Garmin Map60CS. Since it's a portable unit, there is a feature call " Lock on Road". Basically, it forces the pointer to stay on the nearest road on your map. Unlocked, it provides more accuracy when hiking off road.
Anytime you add anything that is not sold by the carmaker, and you have a warranty claim, they may say it caused the problem. They have to prove it, but MM comes into play. Then again it may be a major hassle and costs may be far more than a cost of a PCM.
There could be some reasons your not on the road
Maybe you weren't on the road
GPS is only accurate to so many feet. Maybe it didn't have a good lock and accuracy was less than the width of the road. It's not like it know to the foot where you are.
See
How to Improve GPS Accuracy by Doyle's GIS
maybe it wasn't on long enough to collect enuff data. My portable magallen sometimes takes 5 minutes to be really working right.
Maybe its a new road. When was the DVD updated, 2005? I've been on new roads and its always fun to see you traveling off the map. BTW, the cost of PAG GPS Nav DVDs is not exactly cheap.
the few times that it has happened, I've been driving on old/long established roads and the GPS was working perfectly for a period of time and then ended up just being off by enough feet that I got rounded to the
next
block. I could see on the map the road I was on and the road it thought I was on...
When I've had the problems, I wasn't around especially tall buildings. In fact one time, I was driving down a freeway the whole time.
Geometry of the Satellites come into play also.
I use Survey Grade GPS in my Land Surveying business and I always do mission planning before any control (static) sessions are done to find out what time of day has the best PDOP (Percent Dilution of Position. The measure of the geometrical strength of the GPS satellite configuration.)
I have a
Pioneer
AVIC Z1 in my truck and I get glitches from time to time.
I've been through a lot of automotive and handheld GPS receivers (Lexus, Infiniti,
Pioneer
& Garmin). To me Garmin's stuff seems to work the best. Some may look slicker, but Garmin seems to route you the best.
Anyway, my $0.02 for what its worth.
I have been using GPSs since they first became available to the general public and I have to say that you are exactly right! In fact I was going to say the same thing . . . without the big words.
My first GPS was a Magellan. Every handheld GPS since has been Garmin! (9 and still counting.)
