Altitude measurement using three circular marks

This paper describes a system for a new altitude measurement method, using three circular marks on the landing location for a Vertical Take-Off/Landing (VTOL) aircraft without an altimeter. This system costs less than a radar altimeter, yet it is more accurate than a pressure altimeter at low altitude and simpler than the Carrier Phase Differential Global Positioning System (CDGPS). The proposed method requires only an onboard camera, three circular marks placed on the landing site, and a control computer. The onboard camera must be facing toward the front of the aircraft and configured to detect the shape of the circular mark in image data form. The flight control computer calculates the altitude based on the known distance between the circular marks and the landing point. The accuracy of the proposed method is described in the analysis results section.