Depending on the application, a vehicle coordinate frame is defined as follow : X axis is pointing in Forward direction, Z axis is pointing Down, and Y axis, thanks to right hand rule is pointing to the right of vehicle.
Sensor (body) coordinate frame
This frame is attached to the IMU.
The following diagram shows the body coordinate frame as configured by default. In most situations, the body coordinate frame must be aligned with the vehicle coordinate frame. Sensor alignment in the vehicle can be adjusted by software if the sensor coordinate frame cannot be aligned mechanically. Check section Accounting for misalignment for more details about this software alignment.
Origin of measurements
We have defined the sensor axes directions, but we also need to know where the Origin of this coordinate frame is. This coordinate frame origin is the intersection of the three accelerometers and corresponds to the center of velocity and position measurements.
This origin must be considered when measuring lever arms.
A circular black and white symbol in the mechanical drawings defines and locates this Origin of measurements.
