A count is kept of the number of surfaces traversed, in a variety of three-dimensional imaging systems which are particularly advantageous for use in medical applications based upon data generated by magnetic resonance imaging systems and computerized axial tomographic imaging systems. The system is particularly advantageous in a surgical workstation for planning a wide variety of operative procedures. Surfaces may be selected and displayed simultaneously so as to provide the viewer with a significantly improved knowledge of the relationship of various internal body structures.