Computation of the three-dimensional envelope for roughness measurement

In practice, the instruments measuring according to the E-system refer to a three-dimensional envelope as the measurement is carried out by means of two styli, one a sphere and the other a normal tracing stylus. In this paper, the computational approach to the two-dimensional envelope is reviewed and the extension of the same method to compute the three-dimensional envelope is explained with reference to two-dimensional profiles obtainable with single stylus instruments. © 1974.