Abstract: The invention relates to a three-dimensional measuring device, comprising a rotating 360 degree sensor head, a laser scanner and an extendable mast system. The sensor head contains a 360 degree rotating multi-faceted mirror, which determines total path distance from the laser scanner to a particular target. Angular orientations on both the scanner and the faceted mirrors are calculated by a precision encoding system. The measured total path distance, mast system extension, scanner head rotation, mirror rotation angles, and mast deflection are all used to calculate the location of a target point in 3-D space relative to the scanner. The sensing device can be utilized in the construction and nuclear power areas. In the nuclear power area, the mast system can be extended into a contaminated area which the sensor remains outside the contaminated area, thereby avoiding contamination problems.