A Method to Improve Matching Process by Shape Characteristics in Parametric Systems

Abstract

In current parametric systems, the persistent naming issue (based on edge mappings of intersecting surfaces) is not as fully supported as it should be. Unpredictability and ambiguity of models often happen during design reevaluation within systems. This reference deficiency is widely treated in the literature, especially about non-planar entities during design construction. Although related works ensure the uniqueness of the references to topological entities, they often neglect the shape characteristics of surfaces and give results different from those expected during design reevaluation. We propose in this paper a method to add some additional information about surfaces to improve such works. We compute those information by decomposing surfaces according to hump(s) and/or hollow(s). More precisely, our method use local extremums and inflexion curves to obtain one hump or hollow per sub-surface. The existing matching processes replace every surface with their corresponding subsurfaces, leading to the right edge mappings.Keywords: Persistent naming, shape characteristics, matching process, curved entities. DOI: 10.3722/cadaps.2009.xxx-yyy 1. INTRODUCTION Reuse of part model is an important issue in CAD, architecture or geology domains. Nowadays, feature-based parametric systems enable easy conception and modification of parts. Indeed, it has been estimated that almost 80% of all design tasks consists in adapting an existing model [9] by some simple modification of dimension values, constraint relations and feature definitions. A feature-based parametric system contains the topological representation (i.e. n-Dim entities: vertex, edge, face, volume and topological adjacency relations between these entities), geometric representation (i.e. embedding of these entities) of an object, a set of parameters (characteristics of the object) and a set of constraints (equations or functions) applied to the object. By extension, a parametric modeler is a geometric conception system which not only preserves the explicit geometry of the designed object (so called parametric object or current instance), but also the sequence of commands used for generating it (so called design process, constructive gestures or parametric specification). The majority of current feature-based parametric systems are known as procedural or history-based systems because parametric specification can be regarded as a composition of modeling functions, where each function is attached via its parameters to topological entities defined in some previous states of the model. Referenced entities must then be named in a persistent way in order to be able to reevaluate the model in a coherent way. Particularly, when reevaluation leads to topological

Interactive design space exploration and optimization for CAD models

“…This mechanism is what allows models to re-generate appropriately as users make changes in parameters in the feature history. Since each commercial CAD software has its own referencing scheme, which are proprietary and generally unpublished, we refer the reader to some recent academic works on referencing [Baba-Ali et al 2009;Bidarra et al 2005]. In our work, we use an API to extract this referencing data from the CAD software and leverage this information in order to establish correspondences between shapes.…”