Let's consider a scenario where an IMU device can be attached to any point around the waist. In this case, the direction of motion, like walking, may not necessarily align with the x-axis of the device. How can the angle between the device's x-axis and the direction of motion be calculated?
Sensor fusion methods are used to find the angle between the device's orientation and the magnetic pole. However, what I'm looking for is to determine the angle between the device and the direction of motion.
Thank you
You may combine the three measured accelerations from the IMU into the acceleration vector as a time sequence. This vector, after subtracting the gravitational acceleration, is the one that represents the motion and you may also calculate the three angles between such vector and its three constituents.
If your goal is to know the position and speed of the person as time sequences, then you need to implement a strapdown navigation algorithm and your IMU must have 3 accelerometers and 3 gyroscopes. The navigation algorithm will provide the integrated speed and position vectors of the point on which the IMU is mounted for each time instant, when it is executed. However, the inertial navigation algorithm comprises the integration of the gyros' output and the double integrations of the accelerometers' output with all errors included, leading to exponential accumulation of such errors (Dead-Reckoning Navigation). Correcting for these errors needs sensor fusion with other absolute position and/or speed measurements, such as GPS readings or other references with known coordinates.
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