Two-Prism Surveying Probe

The two-prism surveying probe reaches points on which it is impossible to preserve the verticality of a prism pole or the line of sight between the total station and this prism. Developed at the Centre for Research in Geomatics at Laval University, the probe consists of two miniprisms located along a surveying pole. The two prisms and the probe tip being collinear, three-dimensional coordinates of the point in physical contact with the probe tip can be obtained by taking measurements on each prism and by knowing the distance between these two prisms and the distance between one of these prisms and the probe tip. Moreover, constraints on the distance between the two prisms and on the zenith angle of the probe can be included into the mathematical model. Field tests presented in this paper show that the surveying probe positioning can achieve an accuracy of 0.7 cm (root sum square value) for the three components of the surveyed points.