Many smart systems depend on exact models of their environment. These are gained by tracking objects in their surroundings. When a highly precise system is only available for a small part of the environment, it can be enhanced with a second system to recover the unknown parts. This paper presents a method to recover loss of a precise (optical) tracking system by a less precise (inertial) tracking system. First the rotation from the inertial measurement unit (IMU) and the optical system are aligned. A second step integrates the IMU acceleration two times and removes both times the drift by known initial and end values (first integration: velocity, second integration: position) from optical tracking. The error is backpropagated continuously.