[gps-talkusers] Re: Earthmate to Map Calibration

Rich,

This probably has little to do with the GPS accuracy and everything to do 
with the geo coding of the restaurant's address. We talk about this quite a 
bit in the manual.

Restaurants are in the database based upon a computer projection of where 
they should be based upon averaging of address numbers on a given street. 
Nobody actually drives up to the restaurant and records a GPS position in 
front of the main doors other than you and I.

So the database geo coding gives you a GPS position based on a computer's 
best guess of where the restaurant address may be. There is also the fact 
that many restaurants are not exactly on the street. They may be a ways 
back in a strip mall or sometimes the main door is on one street and the 
address is on a perpendicular street.




At 08:02 PM 8/27/2004, you wrote:
>I have now noticed a consistent difference, or should I say offset, between
>the GPS position and the defined POI position.  This has been observed in
>three different locations as much as 200 miles apart in location.  Let me
>use today's example to explain.
>After dining at a restaurant, I was sitting outside waiting for a cab.
>While sitting there I decided to investigate what was around me.  With the
>Earthmate turned on and indicating that it was picking up 7 satellites I
>pressed f and then enter to search for the poi's nearest me.  In going down
>the list, I came across the restaurant I was sitting in front of.  I set
>this poi as my virtual position and checked the difference between the GPS
>and virtual position.  The response was that the poi was 981 feet southwest
>of the GPS position.  As I said earlier, I have done this two other times in
>locations as far away from where I was today by as much as 200 miles
>(specifically Fresno, Emeryville, and Novato, CA.) always with almost the
>exact same results.  Could the Earthmate be out of calibration, or there be
>some sort of offset being interpreted from the maps by the Braille note?  Is
>there any way I can close this offset?
>Rich Irwin
>rich.irwin@xxxxxxxxxxx

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