Abstract: A computer system is described for producing and representing contour lines of a saddle surface. The contour lines are obtained by a plane intersecting the saddle surface. Depending upon whether the intersecting plane is positioned above or below a saddle point of the saddle surface, two different contour lines result. By means of the height of the saddle point, the computer system is able to decide which of the possible contour lines are the correct ones for the particular case. The contour lines are determined in the form of two intersections, with intersections belonging together being stored in pairs in the computer system. By rearranging, exchanging, concatenating, etc. these intersection pairs, neighbourhood data is obtained defining the neighbour associated with each intersection. By means of this neighbourhood data the computer system is able to represent the polygons made up of contour lines on, say, an image screen.

Abstract: When processing an image it is often necessary to combine parts of its matrix mathematically, e.g. to multiply a part of this matrix with a given weighting function. In this context scalar products of vectors are important operations. The invention provides a coding procedure wherein two of the elements of two vectors are transformed to one encoded element, respectively, and are then stored. This has the result that the calculation of the scalar product requires two encoding operations of the elements and one multiplication of the encoded elements. When calculating another scalar product with at least partly the same elements the encoding operations of a number of elements are already done and the stored encoded elements can be used. This has the consequence that the calculation of this other scalar product requires at least partly no encoding operations but only multiplications of the stored encoded elements.

Abstract: A plurality of individual positions arranged on a surface area are toured. The individual positions are grouped such that each group occupies a continuous partial area in the positioning plane. The groups are ordered so that the partial areas adjoin each other, forming in their totality a geometrical coarse structure. The individual positions are continuously indexed such that their sequence follows the geometrical coarse structure. The indexing of the individual positions is altered in sections such that the time required for sequentially touring all the individual positions of a section is minimized.