1. Method for surveying reference points on construction comprising the steps of: setting respective targets at a plurality of reference points provided on a construction; installing a 3D measuring instrument at a central site where all the apexes of a first polygon are viewable, the apexes of the first polygon corresponding to three or more of the reference points, the 3D measuring instrument collimating the targets to output 3D vectors for the targets; measuring 3D coordinates of the reference points in the first polygon in a predetermined coordinate system, from 3D vectors for the apexes of the first polygon which are collimated by the 3D measuring instrument; moving the 3D measuring instrument to a central site where all the apexes of an n-th polygon G(n) (n being an integer of 2 or more) are viewable, the apexes of the n-th polygon G(n) corresponding to three or more of the reference points whose coordinates have been measured and one or more of the reference points whose coordinates have not been measured; measuring 3D coordinates of the post-movement location P(n) of the 3D measuring instrument and the reference points in the n-th polygon G(n) whose coordinates have not been measured in the predetermined coordinate system, from 3D vectors for the apexes of the n-th polygon G(n) which are collimated by the 3D measuring instrument; measuring 3D coordinates of all the reference points on the construction by repeating a cycle from the step of moving the 3D measuring instrument to the central site of the n-th polygon G(n) to the step of measuring 3D coordinates of the reference points in the n-th polygon G(n) whose coordinates have not been measured; and determining 3D coordinates of all the reference points through network-adjustment calculation based on the measured coordinates of all the reference points.