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:

1) That accelerometers do NOT measure gravity, but rather all the
forces other than gravity which are applied to an object. (In general:
what parts of a system state can and cannot be observed with different
combinations of accelerometers, rate gyros, compasses, and GPS units)
2) Models for the typical noise and offset errors of accelerometers
and rate gyros.
3) Euler angles vs. rotation matrices vs. quaternions
4) Schuler tuning
5) Kalman filters
6) Other types of filters (like sigma point filters)
7) GPS-INS integration, GPS error models

I have yet to find all this information in one location (or even a
significant subset of it, explained in a practical way).

Sean



On Tue, Mar 4, 2008 at 3:03 AM, Apptech <apptech@paradise.net.nz> wrote:
> Good paper on the issues involved in using linear
>  accelerometers as tilt sensors.
>  Having your feet / legs / wheels on the ground at the time
>  rather helps.
>
>
>         http://www.freescale.com/files/sensors/doc/app_note/AN3461.pdf
>
>
>             Russell McMahon
>
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