Sean Breheny wrote: > Thanks! I do wish they had discussed more of the physics, though. > There are a lot of misconceptions out there about what accelerometers > can and cannot do (for example, as you said, you need to know > something about the way it is moving or not moving in order to extract > tilt information from the measured accelerations. Actually, what I'd > like to see is a general app note on inertial navigation, covering, > for example: That's not an app note, that's a whole shelf full of books! > 1) That accelerometers do NOT measure gravity, but rather all the > forces other than gravity which are applied to an object. Huh? The accelerometers I have here measure gravity just fine! Perhaps you meant to say that they measure the net sum all of the accelerations of an object, including gravity. > 2) Models for the typical noise and offset errors of accelerometers > and rate gyros. Very dependent on the implementation technology. > 3) Euler angles vs. rotation matrices vs. quaternions Mainly a question of which works better for the math you need to do in your overall applciation. > 4) Schuler tuning > 5) Kalman filters > 6) Other types of filters (like sigma point filters) > 7) GPS-INS integration, GPS error models Like I said, each one a topic for an entire book, and the choices made depend very strongly on the overall application. For example, I'm working with a client who uses GPS interferometry to measure vehicle absolute attitude (roll, pitch and yaw) at low sample rate, then combines this with relative INS measurements in a Kalman filter to produce an interpolated solution at high sample rate. Fascinating stuff, but he handles all of the theoretical stuff and the application software. I just build the underlying hardware that it runs on. -- Dave Tweed -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist