alexey at feldgendler.ru
Tue Apr 1 16:45:41 CEST 2008
On Tue, 01 Apr 2008 16:09:21 +0200, Christian Beier
<Christian.Beier at stud.tu-ilmenau.de> 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 <alexey at feldgendler.ru>
[ICQ: 115226275] http://feldgendler.livejournal.com
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