Design and styling features using surface deformation

Free form shapes are often used to fulfil both aesthetic and design constraints applied to parametric models currently adopted in CAD environments. Up to now, designers and engineers have mainly access either to indirect manipulations of free form surfaces using their control network or to low-level deformation functions at prescribed points on a surface. Based on a study of the designer's activity, a free form deformation feature is proposed to create CAD tools that better fit their way of working. The introduced category of features is aimed at enforcing the visual effect of the so-called character lines, extensively used by designers to specify the shape of an object. For this reason, in the proposed approach 3D lines are used to drive surface deformation on specified areas. The method uses a mechanical model to generate a deformation process based on the association of such 3D curves with the corresponding curves on the surface to be modified. All these lines are discretised and constraints (position, tangency) at the obtained points are applied. In this paper we focus on the identified user parameters and on their adaptation for the employed mechanical model. The defined feature parameters concentrate on the accuracy and smoothness of the resulting surface, which form prominent characteristics of the overall quality of the surface deformation process. Examples are provided and analysed using curvature maps to address the quality issue of the resulting shape as well as its capability to generate a wide variety of shapes.