From: Michael M. Butler (butler@comp-lib.org)
Date: Tue Dec 21 1999 - 01:59:41 MST
You wrote:
If a GPS receiver is sitting on a car's dashboard it may receive signals
>from several satellites thru the windshield, having a radio view of about
>half the sky. But the other half of the sky would be blocked by the
>car's steel roof, which would likely result in somewhat impaired accuracy
>due to poor geometrics.
Without a good model, and without crunching the numbers, I'm not sure even
to one significant digit _how_ impaired the accuracy would be. As you have
said, it'd vary depending on the moment-to-moment configuration. But that's
the cas ewhen you're out hiking in the wilderness, too. I would expect that
my installtaion's accuracy would still be substantially better than trying
to use the multipath reception inside an REI store.:)
Eyeballing things, I'd say my dash positioning gives a view of about 2/3
sky. '85 Mazda GLC, Left corner of dash, with plenty of driver-side window
in view. If you have a modern car with a slant dash and airbags, your dash
geometry may not permit as much sky to be seen. Score one more for
preregulation technology.
You specifically said
> > > In an automobile, even with the
> > >receiver and antenna sitting on the dashboard, it is unusable.
It was the word "unusable" that I was picking on. I use it. It works. I do
not deny that an external antenna would be better, but I've been being a
cheapskate. :)
MMB
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