Method to determine a present position of an object, positioning system, tracker and computer program

A method (100) to determine a present position (122) of an object (600). The method (100) comprises using (102) an optical positioning system (104) to determine a first preliminary position (112) and using (106) a radio-based positioning system (108) to determine a second preliminary position (114), determining (110) a supposed position (116) on the basis of one of the preliminary positions (112, 114) and combining (108) the supposed position (116) with a previous position (212) of the object to determine the present position (122) of the object, if the supposed position (116) is based on a different positioning system (104, 108) than a previous supposed position (116'). A positioning system (500) with combined optical and a radio-based determination of a position of a tracker (600) and a tracker (600) with an active light source (608).