Abstract: Respective targets 10 are set at a plurality of reference points S1 to S16 provided on a construction. 3D measuring instrument 18 is firstly installed at a central site O of the first polygon G1 that has apexes at three or more of the reference points S, and measures 3D coordinates of the reference points in the first polygon G1 in a predetermined coordinate system, from 3D vectors for the apexes of the first polygon G1 which are collimated by the 3D measuring instrument 18.

Abstract: A position adjusting mechanism 30 with a target 10 mounted thereon is fixed at a plurality of reference points S1 to S16 respectively on a construction 1, and initial 3D coordinates C0 of the targets 10 are surveyed and stored. When deformation or distortion of the construction 1 occurs, a deviation ?C (=Ct?C0) of 3D coordinate Ct of each of the targets 10 from the initial 3D coordinate C0 thereof are detected by a deviation detecting means 26, and each of the targets 10 recovers the initial 3D coordinate C0 by the position adjusting mechanism 30 thereof in accordance with the detected deviation ?C. Preferably, 3D coordinates of the targets 10 are surveyed by a 3D measuring instrument which collimates the targets 10 to output 3D vectors for the targets 10.