How bad is the BMW nav system --- or do I have a flawed copy of the software

"dizzy" > wrote in message
...
> dizzy > wrote:
>
>>Here is a modern GPS module. Note the 26s "cold start" acquisition
>>time, and the 1s "aided start" acquisition time.
>>
>>http://www.u-blox.com/images/downloa...W-09003%29.pdf
>
> Hmm... This article supports the longer "cold" or "factory" time to
> first fix that you guys have been claiming (about 15 minutes).
>
> http://en.wikipedia.org/wiki/Time_to_first_fix

Well indeed. I had assumed the aGPS was using the [known] position of the
mast to get approximate position of the reciver, however the article tells
you it just downloads the almanac if it can (<5kb) as it will be the same
everywhere.

One of the "problems" with the original GPS is that the clear acquistion
signal is ambigous and without the [now released] p-code or the full almanac
the postion repeats around the earth.

Using a Blackberry on T-Mobile it gives a CEP based around the mast you are
using being nearer than any other, but can take 15 minutes to resynch if the
navigation has not been used recently.

Nokia [on O2] are much better and usually fix immediately or in 20-30s.

>
> That doesn't match my industry experience, so I'm wondering if a
> faster but less accuarate postion may be reported before all of the
> Almanac data is acquired.

Indeed it can, but remember these birds are doing five miles per second, so
even a tiny error will put you hundreds of metres out.

As described in the article anything that helps (accurate time, approx
position or knowing you are stationary) helps speed up a fix.

>
> Learned a couple things, anyway.
>

Anyway early 747's had a hole in the cockpit roof through which a specially
designed sextant was used to get a celestial fix. On KAL 007 they got the
fix OK, but then navigated on a magnetic bearing instead of a true one...