A method for measuring shapes of anatomical surfaces.

In the course of a study of biomechanical aspects of carpal tunnel syndrome, a threedimensional point encoder was built to record surface geometries of hand-wrist structures. The point encoder shown in Fig. 1 consists of a pointer that slides axially and rotates in perpendicular planes. The encoder is instrumented with a LVDT (linear voltage differential transformer) and with two potentiometers such that voltages proportional to the axial and two angular positions of the pointer are produced. These voltages of course correspond to the spherical coordinates of the pointer. The encoder voltages were measured via an A-D (Analogue-Digital) Converter and an HP 2100 computer. Each dimension of the system was calibrated by measuring the voltage differences between known positions of the pointer. Scale factors for each channel were expressed as: