GPS

[Ole Kliemann]

On Sun, Jul 13, 2008 at 03:48:14AM -0700, Russell Sears wrote:
> Yes, there is still hope.
> 
> The current software drivers do not save any state between GPS locks, so 
> the GPS device is needlessly re-downloading information from the 
> satellites each time it turns on.  Downloading the data seems to require 
> a much better/more consistent signal than calculating the phone's 
> current position.
> 
> It sounds like a (partial?) fix is in the works.  There were some links 
> to scripts posted to this mailing list a few days ago, but they came 
> with copyright restrictions that prevent redistribution...
> 
> My phone sometimes takes 10 minutes to get a fix, but can track its 
> current position from a car seat (not just near the window), and indoors 
> in my pocket.  It's good enough for in-car navigation, and for use as a 
> speedometer, though with a couple of seconds delay added in.  Also, I 
> see a few meters of jitter when the device is not moving.
> 
> After losing signal in a tunnel for 15-30 seconds, it restored its fix 
> immediately after I left the tunnel.
> 
> Not counting the time to get the initial lock, this behavior is better 
> than what I've seen from some inexpensive name brand gps devices, 
> suggesting the antenna is "good enough", assuming saving and restoring 
> the chip's state works.

I read about this idea in the wiki and posted a comment there. Here's
what I wrote.

I tested the FR outside with internal antenna and did not see a single
sat for 15min. With external antenna I have a TTFS of 33s. If I plug out
the external after the fix is stable, it almost instantly gets lost. I
still see one to three sats but get no fix.
 
So apparently the information obtain through the external antenna is not
enough to assist the internal antenna in getting a fix. Orbit and
positon data should be known to the device by then? If you download this
data from the internet or recalculate it locally, in what way would this
be superior to what I tested?
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