Re: map drift (aubergine2004)
| Quote, originally posted by aubergine2004 » |
| Does anyone experience a drift of car location ...and are there remedies? |
To answer this question properly, we need to look at what the possible causes of inaccuracies could be. In order of probability, they are:
1) The antenna has a poor view of the satellite constellation.
The antenna for the Phaeton GPS receiver is located on the inner side of the rear window glass, approximately in the middle of the vehicle, about two inches down from the roof. There is an illustration showing the antenna location at this post:
Antenna Locations. It is unlikely that anything on the vehicle or attached to the vehicle would block the antenna, unless there was some kind of decal attached to the rear window glass. Driving in 'urban canyons' (streets with high buildings on each side) can result in a loss of satellite reception, but the car will normally cope with this by using dead reckoning - it measures distance travelled by using information from the anti-lock brake system, and yaw (change of heading) by using information from the stability sensor.
The 'worst case' situation would be an obstructed view of the sky right after vehicle start-up, such that the car does not have an accurate position to begin with, and has to use DR right from the get-go. This could happen if you start up in an underground garage, make a few 180 or 360 degree turns to get out of the garage, then emerge onto a street with tall buildings on either side.
It is possible to see how many satellites the system is tracking by looking at the navigation data on the large screen between the two passenger seats. The owner manual explains which page contains this information. The system can track a maximum of 8 satellites, which is more than sufficient. It does not use SBAS (satellite based augmentation services, WAAS in the American implementation, or EGNOS in the European implementation).
If the rear window glass has been replaced on your car, investigate the possibility of antenna problems (loose connection to antenna) first.
2) Early Version Communication Software in the Car
This applies only to MY 2003 and 2004 cars. Two software upgrades are available for these model year cars to solve communication problems within the CAN (Controller Area Network) data bus. These communication problems can result in information not being passed quickly and reliably between the navigation controller (the CD reader) and the rest of the car. One software upgrade is available for the communications hub in the instrument cluster (the instrument cluster upgrade to a software version ending in '21') and that is discussed in great detail here:
Instrument Cluster (MFI, or Y24) - How to reset the Display Screen . Another upgrade is available for the navigation CD reader (to software version 0168), that is discussed in great detail here:
Navigation System inaccurate, gets lost, does not show correct vehicle position. Both of these upgrades are available from your VW dealer, however, due to the small number of Phaetons in North America, you will probably need to do your own research and explain the problem (and the fix) to your dealer.
3) Degradation of Satellite Reception caused by EMI (Electro-Magnetic Interference)
If you drive past a very high powered broadcast station - particularly one that uses frequencies close to those used by the GPS system - you might encounter
momentary degradation of GPS signal reception. There are several such locations in the area of the American National Capital region, they are well known to aviators. If you always encounter the same inaccuracy in the same location, this is likely the cause of the problem. Generally speaking, the problem will not extend beyond about a 2 mile radius, and there are relatively few of these areas in the USA. Close proximity to very large electrical installations (e.g. a generating station, a high voltage switching station) can also cause reception problems, but in this case, the problems usually disappear once you get more than 500 feet away. This means you should not even notice the problem unless you start the vehicle up in the parking lot of the electrical installation.
4) Satellite System is intentionally transmitting degraded information
The NAVSTAR satellite constellation (that being the formal name for the GPS system operated by the American military) is capable of providing highly accurate position information, however, that highly accurate position information can be intentionally degraded within very specific areas whenever the operator of the system deems that to be in the best interests of their security. In other words - if you are driving past sensitive military installations or locations that present a national security concern, you may find that the position information broadcast on the civilian signal (what we use) may be intentionally fuzzy.
My guess - for most Phaeton owners - is that the problem will be caused by item 2, software. Have your VW dealer run a diagnostic scan of your vehicle and determine the software version present in controller 17 (instrument cluster) and controller 37 (navigation CD reader), then, read the information in the previously cited discussions that explains how to flash-update this software.
Michael
