Inserting G1 discontinuities into free-form features for aesthetic design

Abstract

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 and along a line on a surface. Based on a study of designers’ activity, a free form deformation feature approach is proposed to create CAD tools that better fit their way of working. The proposed category of features aims 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 over specified areas. One type of these features is based on G0 or G1 discontinuities along the character lines. Traditionally, a designer using a CAD system creates these features by generating several patches. Our approach proposes a method to create discontinuities on a single patch, using the trimming properties of the surface. 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.