A method for calibrating a three dimensional time-of-flight camera system mounted on a device, includes determining at a first instant a direction vector relating to an object; determining an expected direction vector and expected angle for the object to be measured at a second instant with reference to the device's assumed trajectory and optical axis of the camera; determining a current direction vector and current angle at the second instant; determining an error represented by a difference between the current direction vector and the expected direction vector; and using the error to correct the assumed direction of the main optical axis of the camera system such that said error is substantially eliminated.