TT display error in Alaska

[gd52]

I have tried using two TTs in Alaska (Juneau) and both show current postion about 200 meters west of the true location. I have been told it is the difference in the datum used - NAD 83 vs NAD 27. Anyway to change the system TT uses to correct the error?

 

[dhn]

Are you saying the car icon shows 200 meters west of where the road is ?

If so, connect to Home and download the latest gps quickfix for your unit. See if that helps.

 

[gd52]

Are you saying the car icon shows 200 meters west of where the road is ?

If so, connect to Home and download the latest gps quickfix for your unit. See if that helps.

Yes, the position (car icon) displays about 200 meters west of the car's actual position. I also have a Garmin that does not have the problem. It seems that the TT maps for Alaska are using the wrong datum. TT works fine every else. Just returned from Hawaii with the same unit and all was fine. The following is from a Forest Service site:

"For several years, GPS data have been collected by the Forest Service. In the early years of GPS, data were frequently collected in NAD27 so that they would agree with NAD27 base maps (e.g., topographic and other maps that were produced in NAD27) without any additional effort. In 1992, there was a national mandate to switch geographic datums to the NAD83 datum. For various reasons, this has not been done consistently across the agency. Recently, the Geospatial Advisory Committee has drafted a memo reaffirming this mandate, and has created a timeline for the final mandatory conversion. Conversion of legacy GIS vector data stored in NAD27 or other datums to the NAD83 datum will entail using standard GIS transformation methods."

 

[dhn]

If the dl of a new quickfix file does not remedy the situation (commonly referred to as 'drift') then I'd notify TT Support.

 

[Tim25]

I looked at Google Maps for Juneau. Teleatlas is the source for TomTom maps and Google maps. All of the roads in Google maps are offset from the underlying satellite imagery as you describe.

I don't think there is much that you can do except to report the issue to Teleatlas at: http://mapinsight.teleatlas.com/mapfeedback/index.php

BTW: Garmin uses Navteq map data..
maps.live.com also uses Navteq data...The streets line up with the imagery in Juneau on that site.

 

[flyer1024]

I saw this problem in several areas with my original maps (675). A newer map was the only thing that fixed it. In my case, several spots I regularly drove through always showed me well off the highway. In my hometown, every street, in fact the whole town was off by about a block.

it had to be map inaccuracy. upgraded my maps and it all disappeared.

 

[gd52]

As stated earlier, the supplier of maps for Tomtom is Tele Atlas and Navtec is the map supplier for Garmin. Navtec has corrected for the datum used for Alaska and Tele Atlas has not. Therefore; a Garmin GPS indicates position correctly and Tomtom does not. If looking for a GPS for use in Alaska, don't buy Tomtom, or any other GPS based off of Tele Atlas maps, until they correct the error. This is based on both Tomtom Navigator 6 with the latest maps and a GO 930 with the latest maps.