Construction of Freeform Feature Models With Attachments

In freeform feature modeling, the shape domain of current feature modeling systems is extended with freeform shapes. A challenging task in this context is to develop a method for constructing a feature model in an intuitive, yet unambiguous manner, comparable to the construction methods for regular-shaped feature models. This paper describes a framework in which it is possible to attach a face of a new freeform, volumetric feature instance to a face of a feature instance already in the model. In this framework, features are represented by configurations of freeform definition points, from which the shape is generated. By using geometric constraints on these definition points and other geometric entities within the model, freeform attachments can be realized. Apparent problems that emerge in this context are positioning of the new feature instance on the freeform attach face, fitting the geometry of the new feature instance to the existing model geometry, and maintenance of valid feature model geometry. The framework accommodates for these issues. Two types of attachment, for a freeform extrusion feature respectively a freeform wrap feature, are elaborated. With the attachments presented here, freeform feature models can be constructed in a fully parametrized, constraint-based way, just like regular-shaped feature models.