The efficiency of the work for identifying reference points that are included in photographed images is improved. Targets are located and are photographed from short distances, and the positions of the targets are measured. A 3D reference point model is generated by using the measured positions of the targets as apexes. Then, the positions of the targets that are detected from images taken by a UAV from the air are calculated from a three-dimensional model that are generated by the principle of the stereoscopic three-dimensional measurement, whereby a 3D relative model constituted of a TIN is obtained. After a matching relationship between the 3D reference point model and the 3D relative model is identified, the positions of the targets in the 3D relative model are estimated based on the identified matching relationship, and the positions of the reference points in the images taken from the UAV are estimated.