An apparatus for determining a distance of the apparatus to an object (232, 332) comprising: a radiation source configured to provide a radiation beam (211, 311), a transmissive device (213, 313) with a predefined distance (235, 335) between a first surface (230, 330) and a second surface (231, 331) of the device, wherein the first surface (230, 330) is arranged to reflect a first part (240, 340) of the radiation beam (211, 311), and the second surface (231, 331) is arranged to reflect a second part (241, 341) of the radiation beam (211, 311), a detector configured i) to receive at least a portion of the first part (240, 340) of the radiation beam on a first location on the detector, ii) to receive at least a portion of the second part (241, 341) of the radiation beam on a second location on the detector, and iii) to receive at least a portion of the radiation beam (211, 311) after interaction with the transmissive device (213, 313) and with the object (232, 332) on a third location on the detector, and a processor configured to receive a signal from the detector to determine the distance of the apparatus to the object based on the spatial distance between the first location and the second location, and at least one of the spatial distance between the first location and the third location, and the spatial distance between the second location and the third location. a radiation source configured to provide a radiation beam (211, 311), a transmissive device (213, 313) with a predefined distance (235, 335) between a first surface (230, 330) and a second surface (231, 331) of the device, wherein the first surface (230, 330) is arranged to reflect a first part (240, 340) of the radiation beam (211, 311), and the second surface (231, 331) is arranged to reflect a second part (241, 341) of the radiation beam (211, 311), the first surface (230, 330) is arranged to reflect a first part (240, 340) of the radiation beam (211, 311), and the second surface (231, 331) is arranged to reflect a second part (241, 341) of the radiation beam (211, 311), a detector configured i) to receive at least a portion of the first part (240, 340) of the radiation beam on a first location on the detector, ii) to receive at least a portion of the second part (241, 341) of the radiation beam on a second location on the detector, and iii) to receive at least a portion of the radiation beam (211, 311) after interaction with the transmissive device (213, 313) and with the object (232, 332) on a third location on the detector, and i) to receive at least a portion of the first part (240, 340) of the radiation beam on a first location on the detector, ii) to receive at least a portion of the second part (241, 341) of the radiation beam on a second location on the detector, and iii) to receive at least a portion of the radiation beam (211, 311) after interaction with the transmissive device (213, 313) and with the object (232, 332) on a third location on the detector, and a processor configured to receive a signal from the detector to determine the distance of the apparatus to the object based on the spatial distance between the first location and the second location, and at least one of the spatial distance between the first location and the third location, and the spatial distance between the second location and the third location. the spatial distance between the first location and the second location, and at least one of the spatial distance between the first location and the third location, and the spatial distance between the second location and the third location.