When determining the trajectory of the dummy head during a vehicle crash test, the head is not visible for all cameras during the whole movement, since it, e.g., dips into the airbag. Another possibility is to calculate the trajectory with acceleration and gyro sensor data. When using low-cost inertial measurement units, the calculated trajectory differs from the video analysis by 0.15 metres. The idea is to model possible electrical sensor errors and inaccurate known initial conditions and determine them in an optimisation process in which the video trajectory is taken as the target function. This paper deals with the optimisation process to determine if the optimisation function has a unique minimum. Based on that, several optimisation algorithms are compared and three of them are selected for a detailed comparison. The best of them is selected to show the calculation of a trajectory for a real world crash test.