Introducing Sweep features in Modeling with Subdivision Surfaces Chiara E. Catalano IMATI-CNR - Sez. Genova Via De Marini, 6 16149, Genova, Italy chiara @ge.imati.cnr.it Franca Giannini IMATI-CNR - Sez. Genova Via De Marini, 6 16149, Genova, Italy franca @ge.imati.cnr.it Bianca Falcidieno IMATI-CNR - Sez. Genova Via De Marini, 6 16149, Genova, Italy bianca@ge.imati.cnr.it ABSTRACT In recent times, subdivision surfaces have been considered a powerful representation for shape design. They have been successfully introduced in character animation software packages. In the last few years they have obtained greater attention also from CAD applications due to their potential in overcoming some of the problems intrinsic of spline-based modeling. Anyhow, their major drawbacks are related to the difficulty in constraining the shape of the limit surface and to the limited high level modeling tools to manipulate the shape. In this paper, we propose a feature-based approach to extend the modeling capabilities of subdivision surfaces and to allow users to deal with this new modeling technique closer to the way they are used to. In particular, features obtainable by means of generalized sweep operations are formalized and treated. This type of feature has been chosen because it covers a large set of shapes commonly appearing in industrial products (e.g. car door internal panel cavities, stiffeners, …). Keywords Free-form modeling, feature-based design, subdivision surfaces 1. INTRODUCTION Product design is a complex activity in which the product shape is the major outcome, resulting from a long and complex loop of evaluations and simulations that normally require several and tedious shape modifications to satisfy the given requirements. All these activities are currently supported by computer tools, which offer the advantage of reusing already defined models and avoiding, or at least reducing, the number of the needed physical prototypes. Each involved activity focuses on specific product aspects and uses particular information, thus needing a proper geometric model. It can be noted that not always a continuous and precise representation is used; on the contrary, in many phases discrete models are adopted mainly aimed at simplifying the process. The de-facto standard representation for product design is based on NURBS surfaces, since they guarantee high regularity surfaces, good geometric properties and stable algorithms. Nevertheless, they show limitations concerning the possibility to represent any topology by a unique surface. This causes different kinds of problems when modeling and transferring models to other systems or representations. They are due not only to approximation problems, thus creating gaps or overlapping faces, but also to the user’s creation choices, e.g. models created by stylists frequently exhibit a too large number of patches or too long and narrow patches unsuitable for production purposes. For their nature, subdivision surfaces could overcome this problem defining a discrete surface, which avoids the drawbacks of multi-patch representations. Roughly speaking, a subdivision surface is defined as a sequence of successive meshes that converge to a continuous surface [Zor00]. Subdivision surfaces can be considered in- between continuous surfaces and meshes: on the one hand, they correspond to simple meshes at each refinement step; on the other hand, they converge fast, behaving similarly to a continuous surface: using classical schemes, the limit surface is a C 2 Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Journal of WSCG, Vol.12, No.1-3, ISSN 1213-6972 WSCG’2004, February 2-6, 2003, Plzen, Czech Republic. Copyright UNION Agency – Science Press