When using smoothing splines to estimate a function, the user faces the problem of choosing the smoothing parameter. Several techniques are available for selecting this parameter according to certain optimality criteria. Here, we take a different point of view and we propose a technique for choosing between two alternatives, for example allowing for two different levels of degrees of freedom. T...

In many practical applications, piecewise polynomial surfaces need to be connected by using different smoothness degrees and, in the literature, tensor product spline surfaces of such a kind have been widely investigated. Several problems can arise with tensor product surfaces, for example this choice may cause oscillations far from the shape to be built. Therefore, in some cases spline surface...

We provide su cient conditions for the Bernstein-B ezier (BB) form of an implicitly de ned bivariate polynomial over a triangle, such that the zero contour of the polynomial de nes a smooth and single sheeted real algebraic curve segment. We call a piecewise G-continuous chain of such real algebraic curve segments in BB-form as an A-spline (short for algebraic spline). We prove that the degree ...

In this paper we propose a method to approximate a parametric 3 D-function by bicubic B-spline functions

We present an efficient algorithm for subdividing non-uniform B-splines of arbitrary degree in a manner similar to the Lane-Riesenfeld subdivision algorithm for uniform Bsplines of arbitrary degree. Our algorithm consists of doubling the control points followed by d rounds of non-uniform averaging similar to the d rounds of uniform averaging in the Lane-Riesenfeld algorithm for uniform B-spline...

We prove that the dimension of bivariate tensor–product spline spaces of bi– degree (d, d) with maximum order of smoothness on a multi–cell domain (more precisely, on a set of cells from a tensor–product grid) is equal to the number of tensor–product B–spline basis functions, defined by only single knots in both directions, acting on the considered domain. A certain reasonable assumption on the...

We introduce curvature continuous regular free form surfaces with triangular control nets These surfaces are composed of quartic box spline surfaces and are piecewise polynomial multisided patches of total degree which minimize some energy integral The B ezier nets can be computed e ciently form the spline control net by some xed masks i e matrix multiplications x Introduction Most methods know...

Collocation methods based on quartic splines are presented for second-order two-point boundary value problems. In order to obtain a uniquely solvable linear system for the degrees of freedom of the quartic spline collocation approximation, in addition to the boundary conditions specified by the problem, extra boundary or near-boundary conditions are introduced. Non-optimal (fourth-order) and op...

We introduce curvature continuous regular free-form surfaces with triangular control nets. These surfaces are composed of quartic box spline surfaces and are piecewise polynomial multisided patches of total degree 8 which minimize some energy integral. The B ezier nets can be computed eeciently form the spline control net by some xed masks, i.e. matrix multiplications. k-free-form surfaces need...