Say a body rotates by 90 degrees, then the yaw angle will be 90 which can be calculated using the data provided by IMU.
Now from that point, the body traverses some distance and is again rotated by 90 degree in the same direction. What will be yaw angle shown by the IMU? Will it be 180 degrees or 90 degrees?
In a nutshell what I want to ask is that, is the angle measured from the initial starting point or from the last reference point?
For Roll, Pitch, Yaw, please refer to the above diagram.