1. A method for determining position data of a target object in a reference system from an observation position at a distance from the target object, the method comprising the steps of: a) providing a three-dimensional reference model of surroundings of the target object, the three-dimensional reference model including known geographical location data; b) matching an image of the target object and its surroundings, resulting from the observation position for an observer, with the reference model; and c) determining the position data of the target object in the reference model as relative position data with respect to the known geographic location data of the reference model.