<blockquote style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;" class="gmail_quote">We also need to take into account that accelerometers measure<br>acceleration. If you accelerating or decelerating it will be able to
<br>tell you the magnitude of the force and you can time the duration to<br>find the distance traveled. However, suppose that you are moving at a<br>constant velocity, the accelerometer will measure 0 (zero)<br>acceleration. Most true vehicle dead reckoning systems also include a
<br>sensor for the vehicle speed, which in combination with gps can provide<br>you with something the accelerometer can't. The ability to know how far<br>you have traveled at a constant or accelerating speed.<br><br>
Anyway, since attaching a sensor to the car may not be possible its a<br>moot point. Just thought I would add a few more cents in.<br><br>As a side note... In the US and probably other countries there is a<br>standard for the interface to the car computer. From that interface you
<br>can get the vehicle speed and diagnostic information about how the<br>engine is running. It might be interesting to have some kind of<br>bluetooth car interface to obtain that information and display it for<br>you while you are in your car. Anyone ever heard of anything like
<br>that?<br><br>--Tim</blockquote><div><br><br>yes, accelerometers measure acceleration. The first derivative of acceleration is velocity. Granted errors in the accelerometer compound when deriving velocity, but you've usually got GPS information to calibrate against (As Jeff was saying). A typical dead reckoning system always knows your current velocity, and when GPS goes away, it can apply changes to the velocity by knowing only your current acceleration. The errors associated with this would typically be small enough to not matter during the length of a tunnel or building related GPS blackout.
<br><br>So, an accelerometer (actually, three) is all that is needed for a complete navigation with dead reckoning.<br><br>An accelerometer could have other nifty applications. Here's a few:<br>Tape measure: walk the unit from one corner of a room to another and see both the x and y (even z) distances. Would be very useful for construction and event production professionals
<br>Games: Use the entire device as a steering wheel in a car game, or yoke in a flying game<br>Pedometer: if accurate enough, could count actual steps walked and convert that to calories burned. Or could count paces when following a pirate's treasure map.
<br>Subway system: Could tell you where you are, and wake you up or alert you when riding the subway. (Since no one can usually understand the announcements)<br><br>--Steve<br></div><br>