Inertial Navigation - transforming from body to global frame

Hey there,

I´m working on a little INS project and I´m a bit confused about the reference frames. Actually: I don´t get why I have to transform from body to global frame and how to do it. Why can´t I just integrate the Acc signals and take the position from it? So far I understand that I have to calculate the attitude first from the gyro and take the results to transform from acc frame b(ody) to acc frame g(lobal). But yeah, I simply don´t geht why and how to implement it. What´s the gain? I read lots of reports and papers but they are mostly very abstract or to complex for me since my math skills are not the best. As far as I know it´s just a simple matrix multiplication but I don´t really get how to derive it. A tutorial for dummies or code snippet would help me a lot. Any ideas?

Thanks,

Michael

This collection of technical notes is very helpful, and incidentally explains why you can't get position from a consumer grade accelerometer: http://www.chrobotics.com/library

For this project, math skills are very useful.

..I have to calculate the attitude first from the gyro and take the results to transform..

The major issue with that is the MEMS gyro is not the same gadget as the "old one" (a heavy wheel fast rotating inside three gimbals)..
The MEMS gyro shows an angular velocity, while old gyro shows an attitude. The error of a MEMS gyro (when integrating reasonably fast) is few degrees in a several seconds, while the error of the old one is few degrees in an hour (the best ones).