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Navigation system accuracy ?

8K views 17 replies 13 participants last post by  Bill Merchant 
The GPS itself is VERY accurate. Only when it loses contact is the error noticible and then the system just does a linear extrapolation while it is reacquiring.

The map database is variable, but typically excellent. In urban LA it even knows about the left freeway exits, which is a big help if you aren't familiar with the area. It also performed amazingly well in Napa. Yesterday in Santa Ynez we found a few wineries where the tasting room just wasn't at all where the system thought the "winery" was. We also tried to find the "Hitching Post" restaurant (can you tell we watched "Sideways" too recently) and it turned out that the database had only the street and not the street number for it, so it stuck it at the intersection of that street and
the nearest major highway in the town. Be nice if it had a warning for that! We figured it out by closely studying the "info".

OTOH, it got us very close to a very obscure address out in the middle of nowhere in Paicines, CA. The town of Paicines consists of a country store with attached bar and dance hall. It wasn't perfect, the nav system announced the destination maybe a quarter mile before the driveway, but I actually thought it was pretty impressive. I suspect it does some form of interpolation or extrapolation to get street addresses in remote areas.

The one thing it did do that was mysterious was to insist on routing us to the I5 after we were pretty sure we'd chosen a route up the 101 from the 3 route choices. We did confuse it by missing some turnings and choosing a route back other than what it was suggesting, causing it to recalculate the route several times. We eventually forced it off that course by setting a preferred road, but we were never sure if we did something we didn't mean to, or if it somehow reverted to "Quick1" during the recalculation process. By the time we did that, the time estimates for the route it was trying to force us on was almost twice the time estimate for the corrected route once we input the preferred road (5 hours vs 7.5). Maybe we just annoyed the "Nav Lady" by ignoring her, and she wanted some revenge?
 
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