Geometric Hermite curves with minimum strain energy

The purpose of this paper is to provide yet another solution to a fundamental problem in computer aided geometric design, i.e., constructing a smooth curve satisfying given endpoint (position and tangent) conditions. A new class of curves, called optimized geometric Hermite (OGH) curves, is introduced. An OGH curve is defined by optimizing the magnitudes of the endpoint tangent vectors in the Hermite interpolation process so that the strain energy of the curve is a minimum. An OGH curve is not only mathematically smooth, i.e., with minimum strain energy, but also geometrically smooth, i.e., loop-, cusp- and fold-free if the geometric smoothness conditions and the tangent direction preserving conditions on the tangent angles are satisfied. If the given tangent vectors do not satisfy the tangent angle constraints, one can use a 2-segment or a 3-segment composite optimized geometric Hermite (COH) curve to meet the requirements. Two techniques for constructing 2-segment COH curves and five techniques for constructing 3-segment COH curves are presented. These techniques ensure automatic satisfaction of the tangent angle constraints for each OGH segment and, consequently, mathematical and geometric smoothness of each segment of the curve. The presented OGH and COH curves, combined with symmetry-based extension schemes, cover tangent angles of all possible cases. The new method has been compared with the high-accuracy Hermite interpolation method by de Boor et al. and the Pythagorean-hodograph (PH) curves by Farouki et al. While the other two methods both would generate unpleasant shapes in some cases, the new method generates satisfactory shapes in all the cases.