On Tue, 01 Apr 2008 16:09:21 +0200, Christian Beier
<[EMAIL PROTECTED]> wrote:
Unfortunately you need accurate speed to be able to get usable data
from accelerometers for that. That's why some GPS modules have an
interface for tachometer.
May be the history of GPS could be used to approximate the speed. Of
course, it's not accurate but when you assume facts like:
* you have already slow down your vehicle before entering the tunnel
* you will never accelerate in the tunnel
* max tunnel length of 3km
the variance should not be so huge. At least it's easier than connect
the tachometer. The other question is: do you really need the correct
position in the tunnel? If you know the position when the signal get
lost and know that you are in that special tunnel it should be enough.
Of course, it makes more sens in urban "tunnels" between huge buildings.
In Norway, where I live, some tunnels are very long and even sometimes
contain internal enter and exit lanes, so there can be more than one way
to go. My Garmin navigator tries to estimate where I am basing on the
speed I had when entering the tunnel, so sometimes it notifies me of an
internal exit I have to take too late.
--
Alexey Feldgendler <[EMAIL PROTECTED]>
[ICQ: 115226275] http://feldgendler.livejournal.com
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