Most car-based navigation systems use gyroscopes and speed sensors in
addition the the GPS. ETAK (now Tele Atlas) built a working navigation
system back in the mid 80's without GPS. It used wheel sensors only
(gyroscope optional) and used the wheel sensors to calculate both speed
and direction of turn (direction found by different speed on left and
right wheel). It worked very well and even adjusted itself for tire wear
etc.

Even systems with GPS rely heavily on the speed sensor and gyroscope
since this data is available much sooner (the gyroscope will tell you
that you are turning WHILE you are turning. The GPS can only tell you
that you have turned after you have driven in the new direction long
enough to establish two nes GPS locations). The system will use GPS to
calibrate the speed sensor, so the speed sensor data is very accurate.

As a technicality, one could argue that the speed sensor really is a
distance sensor. It gives a number of pulses pr mile regardless of how
fast you are going. Unless you have some sort of time reference, the
"speed" sensors will only give you mileage.

Dick wrote:
>
> I'm just quoting from the Honda manual, page 3. "In addition, a
> gyroscopic sensor and a speed sensor in your car keep track of the
> direction and speed of travel at all times."
>
> Dick
>
> On Mon, 28 Jul 2003 08:14:06 -0500, TL <tlehman@visi.com> wrote:
>
> >I agree. The signal would have been lost. I'm curious, though about
> >the sensors you mention. My handheld simply extrapolates when it
> >experiences signal loss, ie, continues in the same direction at the
> >same speed. After some predetermined time, it goes into a holding
> >pattern and reports the lost signal. Obviously an auto-based system
> >*could* have a speed sensor, but I'm surprised if it does. Calculating
> >speed from the GPS readings should be much more accurate than the
> >speed sensor in the car and it provides a vector speed (direction and
> >ground speed).
> >
> >I'm not saying you're wrong. I'm just curious about the source of your
> >information about the navigation system having a gyroscope and speed
> >sensor. I've never heard that before.
> >
> >Tom