Unsupervised generation of polygonal approximations based on the convex hull

•A new approach for generation of polygonal approximations based on the convex hull of contour is proposed.•The proposed algorithm takes into account the symmetry of the contour.•A final improvement process is applied to increase the quality of the polygonal approximation.•The new algorithm is non-optimal but unsupervised (automatic), because no parameters have to be set or tuned.•Experiments using a public available dataset show that the new proposal outperforms other unsupervised algorithms.