In general, the camera is installed on the gimbal and fixedly connected to the drone, and the gimbal has two degrees of freedom of rotation in the horizontal and vertical directions. In practice, it can be considered that the origin of the camera system coincides with the origin of the machine system.
The pitch, roll, and yaw calculated by our accelerometer are from the navigation system n to the aircraft system b. In computer vision, it is also necessary to convert the attitude from the machine system to the camera system.
Camera coordinate system:
camera coordinate system (c system): take the principal point of the image square of the optical system as the origin O; the X axis is parallel to the imaging plane coordinate system, and the right direction is positive; the Y axis is parallel to the longitudinal axis of the imaging plane coordinate system, The downward direction is positive; the Z axis points to the observer, and the downward direction is positive; constitutes a right-handed coordinate system.
Body coordinate system:
The machine system is generally in front of the X axis, the right is the Y axis, and Z is pointing to the ground. It is the order of the front bottom right.
If the camera is fixed at the front of the drone, then the transformation matrix:
