[gps-talkusers] 300 feet off 33 okay

To summarize this discussion, there are at least 3 factors that go into 
accuracy or shall we say inaccuracy considerations.

1. Map data error. I believe the Tele Atlas spec is something like 12 meters 
accuracy but I am sure this varies depending upon how they obtained the data. 
One can learn about the street data quality by checking the distance to the 
intersection when standing at it or by asking for a pedestrian route and then 
noting where the waypoints are set and how they trigger when you come close to 
them. As mentioned, if a user records a point, the GPS accuracy when that point 
was recorded calculates against the error when playing that point back. Those 
errors could cancel each other out or they could add together.

2. GPS signals: The quoted average is 30 feet. We all know that GPS accuracy 
ranges from 10 feet to 100 feet or more.

3. Distance to the center of the intersection: As Chris points out, the center 
of the intersection is where the two mid lines cross from the intersecting 
streets. In astreet with 2 lanes each way, this distance could be50 feet.

A reminder that there is a document called GPS Accuracy contained in the 
documents folder that comes with the Sendero GPS or within the documents zip 
file on our download site. There is lots of good things to learn in this 
document about accuracy factors.

Mike

At 08:14 PM 3/14/2007, you wrote:
>Hello:
>
>Many thanks for the responses.  But I am still confused.  I am not near a 
>military base.  The problem is not limited to street addresses, but to 
>intersections as well.
>It is just odd that I can be  an intersection, standing a few steps from the 
>corner and the GPS tells me that I am 180 feet from the corner.  THE same time 
>the GPS tells me that I have good reception.
>Thank you again.
>
>JD

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