Renner, G.K. BO and H.A. TUCKER2015-09-292015-09-2919841017-4656http://dx.doi.org/10.2312/eg.19841004Technical objects which are typically described by free-form surfaces, usually also contain conventional elements (planes, cylinders, cones). Consequently, methods and systems for defining free-form shapes are advantageously complemented by description of simple geometrical elements. In the paper, known methods of computational geometry are examined from the point of view of describing curves containing straight line sections. Moreover an analysis of the accuracy of approximating a circle by these methods i s given.10.2312/eg.19841004