3D Object Representation for Physics Simulation Engines and its Effect on Virtual Assembly Tasks

Abstract

Physical based modelling (PBM) uses physics simulation engines (PSE) to provide the dynamic behaviour and collision detection of virtual objects in virtual environments emulating the real world. There exists a variety of PSEs, each one with pros and cons according to the application in which they are employed. Each physics engine uses its proprietary collision detection algorithm. Collision detection is a key aspect of assembly tasks and its performance is dependent on the way virtual objects are represented. In general, objects can be divided into two groups: convex and concave, the latter being the most common and challenging for collision detection algorithms. This study reports on three different methods to represent concave objects. GIMPACT, Hierarchical Approximate Convex Decomposition (HACD) and Approximate Convex Decomposition (ACD), which are evaluated and compared based on their collision detection performances. An exact convex decomposition algorithm, named as ConvexFT, is also proposed and analyzed in this paper. Finally the performance of the three existing methods and the ConvexFT proposed approach are compared in order to assess which model representation algorithm is best suited for haptic-virtual assembly tasks.

A new methodology to evaluate the performance of physics simulation engines in haptic virtual assembly

“…The two spheres are created using different collision shape representation algorithms, i.e. primitives, GIMPACT (2011), HACD (Mamou and Ghorbel, 2009), and ConvexFT (Gonzalez et al, 2012). When using primitives, the collision shape of the spheres is created by specifying only its diameter.…”

A UNITY Sketch Based Modelling Environment for Virtual Assembly and Machining to Evaluate DFMA Metrics

“…Within the unity environment this problem is usually addressed by either an approximation made from primitive collision shapes (created manually by the user) or with the use of automatically generated convex hull collision meshes. The convexFT [46] technique is implemented here.…”