I'm driving off road I guess!?

[underdog01]

I just purchased a lowrance expedition c and map create 7. When I drive down the road the marker is sometimes off the road on the map. Is this normal? Am I expecting this the gps to be too accurate? I understand that some roads will be missing or inaccurate but the gps shows I'm driving on lawns. Am I doing something wrong or are my expectations just to high? Thanks for your replies.

[lbendlin]

This is "normal" behavior. GPS is only accurate to +- 15 metres, so lawns and sidewalks are always part of the show. Add to that the map inaccuracies and you'll be alright.

Some programs use "snap to road" rendering but I don't like that - it hides the map errors from me.
_________________
Lutz

Report Map Errors here:
TomTom/TeleAtlas NAVTEQ

[robertn]

The maps are generally far less accurate than the GPS. GPS HDOP Horizontal error) is typically less then 5 meters, often below 2 meters, when there are more than 5 sats used for the fix, this is common when using a newer (SiRF III or equivilent) GPS.

Also when you get down to real detail you need to understand the difference in the datums (the mathmatical model for the surface of the earth used in calculations). This can add even more errors if the map datum and the GPS datum are different and are not correctly converted. A non trivial calculation in most cases, and often not converted bacause it is "close enuf"

In summary - you, like many people, are probably expecting far too much from the technology.

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