SURFACE COLLISION DETECTION WITH THE OVERLAPPING BOUNDING BOX BETWEEN VIRTUAL PROTOTYPE MODELS

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1 International Conference on Advanced Research in Virtual and Rapid Prototyping SURFACE COLLISION DETECTION WITH THE OVERLAPPING BOUNDING BOX BETWEEN VIRTUAL PROTOTYPE MODELS Mauro Figueiredo 1,2, Terrence Fernando 1 1 Centre for Virtual Environments, University of Salford, University Road, Salford, UK mfiguei@ualg.pt; T.Fernando@salford.ac.uk 2 Escola Superior Tecnologia, Universidade do Algarve, Portugal - mfiguei@ualg.pt Abstract This paper identifies requirements and proposes a surface collision detection algorithm for assisting in assembly/disassembly and maintenance verification operations in virtual prototype environments. Virtual prototype models are defined as a collection of surfaces. Available collision detection toolkits for virtual environments are based on polygons. The integration of surface knowledge into the design of the collision detection algorithm, contributes for the development of a better real time collision detection algorithm for supporting assembly and maintenance simulations. The algorithm presented in this paper, takes advantage of the scene graph structure and determines, for each pair of colliding objects, the intersecting surfaces. The virtual prototyping environment uses this knowledge for the automatic recognition of geometric constraints during user interaction in assembly and maintenance operations. This paper also introduces the novel concept of Overlapping Axis-Aligned Bounding Boxes (OAABB for improving the overall complexity of the collision detection algorithm. Keywords Virtual Prototyping, Virtual Environments, Collision Detection. Introduction Today's development of industrial products faces high requirements. Manufacturing companies need to produce high quality products, at low cost, to be marketed earlier than those of the competitors. Products must satisfy consumer requirements, developed fast and of high quality. To this extent, many manufactures are adopting concurrent engineering in an attempt to reduce the lead-time for new products and improve their quality while reducing manufacturing costs. Concurrent Engineering (CE is a systematic approach to the integrated concurrent design of products and related processes. It encourages the integration of traditionally separated product development phases in the design of the product. In CE issues of the product life cycle, such as manufacturability and maintainability, are considered and improved at early stages in the design of a product. This reduces unforeseen problems creeping into the design as it progresses through its life cycle, consequently saving both time and money while improving product quality. In this process, different engineering disciplines are considered simultaneously and computer support is required to manage the huge amount of complex product data. Current software tools do not fully support all stages of the product development cycle, restricting the applicability of concurrent engineering concepts. There is still a lack of software tools to address assembly/disassembly operations and maintenance verifications [1, 2]. Development teams continue to build a physical prototype to assess if a human worker can assemble a part or component, and if it can be disassembled later on for service and maintenance. But, a physical prototype is expensive, time consuming and increases the time to market the product. Frequently, a physical prototype is available very late in the design process, making it difficult to integrate any major changes. Pratt [3] points out that up to 70% of the total life cycle costs of a product are committed by decisions made in the early stages of design. In fact, it has been recognized the benefits of using virtual environments and virtual prototyping for assembly and maintenance verification and it has been identified has an opportunity to improve the development process and a topic of ongoing research [1, 2, 4]. In this paper, we present a collision detection algorithm focused in the development of a better real time collision detection algorithm for supporting assembly and maintenance simulation in virtual prototyping environments. First, we present the requirements of a collision detection manager for virtual prototyping environments. Virtual prototype

2 models are defined as a collection of surfaces. Available collision detection toolkits for virtual environments are based on polygons. The integration of surface knowledge into the design of the collision detection algorithm, contributes for the development of a better real time collision detection algorithm for supporting assembly and maintenance simulations. The algorithm presented in this paper, takes advantage of the scene graph structure and determines, for each pair of colliding objects, the intersecting surfaces. The virtual prototyping environment uses this knowledge for the automatic recognition of geometric constraints during user interaction in assembly and maintenance operations. We also introduce the novel concept of Overlapping Axis-Aligned Bounding Boxes (OAABB for improving the collision detection performance. A straightforward algorithm for finding collisions is of square complexity. The algorithm that we present uses the OAABB to reduce the complexity and improve performance. Virtual Prototyping Framework The ongoing research at the Center for Virtual Environments at the University of Salford is concerned in the development of a unified platform, for virtual prototyping. A goal of this research is to integrate expertise from design, engineering, testing, manufacturing and maintenance in a unified concurrent engineering framework in a virtual environment. The integration of different stages of the product development cycle in a unified virtual prototyping leads to more effective rapid prototyping. In this environment, a virtual prototype is built from a three-dimensional CAD drawing. The 3D virtual model gives complete information about the product earlier in the development cycle. Conventional prototyping can take weeks or months. Virtual prototyping is quicker and reduces the cost of building prototypes as opposed to conventional methods. In this virtual prototyping framework, a 3D virtual model of the product is used within the different stages of the product life cycle. The virtual model behaves as the physical prototype enabling the simulation of all aspects of a product, such as, mechanical design, kinematics, dynamics, testing and maintenance, in a unified framework. In this way, more analyses of the design can be performed before there is a need to build the physical prototype, which is more difficult to modify, thus reducing furthermore the costs and the time to market the product. The architecture of the proposed unified virtual prototyping environment is shown in figure 1. Visualization Virtual Prototyping System Interaction Physical Realism Behaviour Collision Detection Constraint-based Geometric Figure 1 - Architecture of the unified virtual prototyping environment. The framework for the virtual prototyping environment consists of three main components: visualization; interaction and behavior simulation. These components are commonly present in virtual environments applications. The function of each of these components is as follows: Visualization: This component is responsible for the presentation of high-level 3D graphical and multimedia scenes. Interaction: This module gives to the user the feeling of direct interaction with the application, rather than with a computer. The user is able to interact naturally in 3D by touching, feeling, grabbing, moving and manipulating objects, as he/she would do in the physical world. Behavior: This module supplies the functionality that helps in the simulation of the reality. It contributes to the enrichment of the creation of the sensation of manipulating a real world. Three modules can be identified: 1 Physical Realism : This component is responsible for the simulation of physical properties such as: solidity, gravity, elastic collisions, and others. The physical realism manager includes generic behaviors that contribute to the simulation of reality. When an object is dropped, it falls according to the gravity laws until it stops on the floor. An object like a balloon rises in the air until it reaches the virtual room ceiling. Each object has its individual behavior, knowing how to react to various stimuli the environment exerts upon it. 2 Constraint-based Geometric : This component is responsible for modeling interactive assembly and disassembly tasks. This manager automatically recognizes geometric constraint relationships between the assembly components. It also automatically removes the constraint relationships appropriately, when the user is disassembling a model. The constraint-based geometric module also manages constraint relationships while simulating constrained motion. 3 Collision Detection : This module is responsible for finding precisely and interactively collisions between the geometric surfaces. The collision detection manager checks if any objects are

3 colliding in the world at any moment. For objects that do collide, the system determines appropriate behavior to simulate reality. For assembly/disassembly and maintenance simulations, the collision detection manager determines the colliding surfaces passed to the constraint-based geometric manager. This information is used for the automatic recognition of geometric constraint relationships among the assembly components and to remove the geometric constraint relationships appropriately during user interaction. Collision Detection Requirements for Maintenance in Virtual Prototyping The Virtual Prototyping Group at the Centre for Virtual Environments at the University of Salford is also working in the exploration of the applicability of virtual reality in maintenance simulation, which involves complex object interaction and control [2]. Work is being carried on in the development of a simulation environment that allows designers and engineers to assess maintenance tasks before any physical prototype is built. In a maintenance simulation scenario, it is necessary to allow the user to interactively carry out assembly and disassembly operations on the virtual prototypes in a realistic way. These operations rely in a set of geometric constraint relationships that are automatically established or removed as the user manipulates the assembly components. On the other hand, in such environment, the three-dimensional virtual prototypes need also to simulate physical properties realistic. These processes use the collision detection for: providing collision response to stop object penetration; establishing a set of geometric constraints relationships; simulating constrained motion; simulating kinematics motion and sliding; assisting users to carry out precise object manipulations. This section presents problems identified from our experiments and characteristics of a collision detection manager to be developed for assisting in assembly and maintenance operations in virtual prototyping environments. A collision detection component for this purpose should: (a determine collisions based on surfaces; (b determine collisions precisely; (c determine collisions interactively. A collision detection manager for assisting in assembly and maintenance operations in virtual prototyping environments should be surface based. Wimalaratne [5] identifies the need of developing efficient surface-based collision software to integrate a virtual prototyping system for assembly simulation. Virtual prototyping models, generated by Computer-Aided Design (CAD systems, are surface-based. There are several publicly available collision detection toolkits for virtual environments: I-COLLIDE [6]; RAPID [7]; V-COLLIDE [8]; SOLID [9]; QuickCD [10]. These collision detection managers support polygonal models [11], disregarding all the surface data of the CAD model. The awareness of all the colliding surfaces is a valuable information for the constraint manager, enabling the automatic recognition of constraints and avoiding penetrating objects. Consider the example presented in figure 2. The user is manipulating a shaft part. For the recognition of constraints, the designer uses the knowledge of the intersecting surfaces. This is an issue that current collision detection toolkits are lacking. Publicly collision detection implementations can determine exactly intersecting polygons. These implementations do not provide information about intersecting surfaces. (a (b Figure 2 - The simulation of solidity is disabled. (a The shaft is partially inside a mechanical component. In (b there are intersecting surfaces that can be selected for the recognition of constraints. A collision detection manager for assisting in assembly and maintenance operations in virtual prototyping environments should find collisions precisely. In the simulation of assembly and disassembly operations, finding precise collisions is an important task for achieving realistic behaviour [12]. When assembling two components, it is necessary to find which parts are colliding, to determine possible constraints and simulate solidity. When simulating the dynamic behaviour of a virtual prototype, collision detection is used again to determine the exact interactions between different components. If a user wants to grab a virtual prototype, a collision check must be done to guarantee that he is touching it. Figure 3 shows an example that emphasizes the importance of exactly finding collisions for the recognition of constraints in assembly operations.

4 Scene Graph Objects O 1... O m (a (b Figure 3 - In the digger case study scenario it is used the concept of virtual sensor based on bounding volumes. (a Identification of a constraint between the two highlighted surfaces. (b The two components are assembled unrealistically. S 1... S i Polygons P 1 P 2... P j P 1 P 2... P k Figure 4 - Virtual prototyping scene graph. Figure 3-a presents a situation where there is no contact between the two highlighted surfaces. However, it is automatically recognized a constraint between the two surfaces, as a result of the determination of an overlap between the two corresponding bounding volumes. If the user accepts the recognized constraint, the two components are unrealistically assembled as it is presented in figure 3-b. Collision detection algorithms implemented only with bounding volumes are ineffective in automatically identifying geometric constraints correctly. A collision detection manager for assisting in assembly and maintenance operations in virtual prototyping environments should find collisions interactively. Finding collisions in a three-dimensional environment can be a very demanding task. In some environments it can easily consume up to 50% of the total run time [13]. In real industrial case studies tested and evaluated at the Center for Virtual Environments at the University of Salford, 3D virtual prototypes can be very complex with thousands of primitives. Developing collision detection algorithms for complex environments is an open research issue [14]. Furthermore, maintaining the user of a virtual prototyping application engaged and providing the illusion of being immersed and working interactively in the system requires a constant high frame rate. In the worst case, it is required an update rate of at least 10 Hz. Collision Detection Architecture This section presents a novel algorithm for finding collisions in a virtual prototyping environment. The collision detection manager described, in the following paragraphs, takes advantage of the scene graph structure (figure 4 available from CAD models. For each pair of objects it determines the colliding surfaces. The proposed algorithm for the determination of colliding objects and surfaces in a virtual prototyping scene graph is done in three steps (figure 5: 1 Filter Objects ; 2 Filter ; 3 Polygons ion. Scene Graph Filter Objects Filter Polygons ion O i, O' j, OAABB(O i,o' j, OAABB(,S' l Colliding Figure 5 - Collision Detection Architecture. Filter Objects This manager determines possible objects candidates for collisions. This stage uses the axisaligned bounding box (AABB of each object. If a pair of axis-aligned bounding boxes do not overlap, then the corresponding two objects cannot intersect and this pair of objects is filtered out. Two objects, O i and O j, are candidates for collision if the corresponding axis-aligned bounding boxes overlap. In this case, the collision detection manager determines the Overlapping Axis-Aligned Bounding Box, OAABB (O i, O j, of the two objects (figure 6. This is determined as the volume that is common to the two overlapping axis-aligned bounding boxes. A novelty of the proposed algorithm is the use of the OAABB (O i, O j of the two objects in the next step of the collision detection process.

5 OAABB(O 1,O' 2 OAABB(O 1,O' 2 AABB(S 2 AABB(S' 1 AABB(O' 2 S 2 S' 1 S 2 S' 1 S' 2 O 1 O 1 S 1 S' 2 S 1 AABB(S' 2 O' 2 O' 2 S' 3 AABB(S 1 S' 3 AABB(S' 3 AABB(O 1 S 3 S 4 Figure 6 - The Overlapping Axis-Aligned Bounding Box (OAABB concept shown in 2D. Filter This process determines possible surfaces candidates for intersection. For every pair of objects candidates for collision determined in the previous step, the algorithm filters out surfaces that cannot intersect. This is a novelty of the present algorithm. The determination of precise collisions in a virtual prototyping environment considers the available surface data from the CAD model. The proposed algorithm uses the axis-aligned bounding box of each surface and the overlapping axis-aligned bounding box determined in the first step (figure 7. For two objects, O i and O j, a straightforward implementation for finding pairs of surfaces candidates for collision, checks for intersection every AABB of each surface from one object against every AABB of each surface from the other object (figure 8. This approach is of complexity O(n 2, n is the number of surfaces of each object. To achieve a better performance, it is proposed the use of the OAABB (O i, O j determined from the two candidates objects for intersection. Two surfaces and S l, are candidate for intersection if they also intersect the OAABB (O i, O j (figure 7. In this way, surfaces whose AABBs do not intersect the OAABB (O i, O j are filtered out. The remaining m surfaces of each object are than intersected to find if their corresponding AABBs are overlapping. This step is also of complexity O(m 2, but m is the small number of remaining surfaces of each object. In the example shown in figures 7 and 8, there is an overhead of 50% of the straightforward implementation over the approach based on the OAABB. For every pair of surfaces and S l, whose AABBs overlap, it is determined the OAABB (, S l of the two surfaces, to be used in the next step of the collision detection manager. A list of pairs of surfaces candidates for collision and the corresponding OAABB is the output of the filter surface manager. Figure 9 presents the final architecture of the filter surfaces manager illustrating this procedure. S 3 S 4 AABB(S 3 Straightforward Approach O(n 2 (AABB(S 1, AABB(S' 1 (AABB(S 1, AABB(S' 2 (AABB(S 1, AABB(S' 3 (AABB(S 2, AABB(S' 1 (AABB(S 2, AABB(S' 2 (AABB(S 2, AABB(S' 3 (AABB(S 3, AABB(S' 1 (AABB(S 3, AABB(S' 2 (AABB(S 3, AABB(S' 3 (AABB(S 4, AABB(S' 1 (AABB(S 4, AABB(S' 2 (AABB(S 4, AABB(S' 3 AABB(S 4 Figure 7 - The filtering surface process shown in 2D. Surface Filter Implementation OAABB Approach (AABB(S 1, OAABB(O 1,O' 2 (AABB(S 2, OAABB(O 1,O' 2 (AABB(S 3, OAABB(O 1,O' 2 (AABB(S 4, OAABB(O 1,O' 2 (AABB(S' 1, OAABB(O 1,O' 2 (AABB(S' 2, OAABB(O 1,O' 2 (AABB(S' 3, OAABB(O 1,O' 2 (AABB(S 1, AABB(S' 2 Figure 8 - Comparison of two approaches for filtering surfaces. Filter Filter with Bounding Boxes AABB( OAABB(O i,o' j AABB( AABB(S' l O i, O' j, OAABB(O i,o' j AABB(S' l OAABB(O i,o' j, OAABB( Figure 9 - The filter surfaces manager architecture. Polygons ion This manager is responsible for determining precisely intersecting polygons. For every pair of objects candidates for collision, the previous stage determined a set of pairs of surfaces that can possible collide. Finding precisely if two objects intersect, needs checking for collision every pair of

6 polygons from this set of surfaces. ing two polygons is an expensive computational operation. Axis-aligned bounding boxes of each polygon can be used to reduce the number of such operations in a process for filtering polygons (figure 10. obtained, in the determination of the intersecting surfaces, by the algorithm described in this paper., OAABB( O 1 S 2 S 1 OAABB(S 1,S' 2 S' 1 Polygons ion P 1 P 2 P 3 P' 3 S' 2 P' P' 1 2 O' 2 Filter Polygons with P' P' 5 4 Bounding Boxes P 4 S' 3 P 5 S 3 S 4 Figure 10 - Filtering polygons using AABBs and OAABB in 2D. AABB(P m OAABB(,S' l AABB(P' n OAABB(,S' l Pairs of polygons whose AABBs do not overlap, cannot intersect and are discarded. At this point, the proposed algorithm introduces the novelty of using again the overlapping axis-aligned bounding box. At this stage, the polygon intersection manager uses the overlapping axis-aligned bounding box, OAABB (, S l, between every pair of surfaces candidates for collision. Two polygons can possible collide if and only if their AABBs intersect the OAABB (, S l. Therefore, the first operation accomplished in this stage consists in, testing for each polygon of and S l, if its AABB intersects the OAABB (, S l. If there is no intersection then the corresponding polygon is filtered out. AABBs pairs of the remaining polygons are then intersected. Those non-intersecting pairs are filtered out. These previous steps filter out every pair of polygons that do not intersect, because theirs corresponding axisaligned bounding box do not overlap. In the end, there are a small number of pairs of polygons candidates for collision. The final step is to proceed with the intersection of pairs of polygons. If there is a pair of intersecting polygons then the corresponding surfaces intersect. A list of colliding surfaces is constructed. Figure 11 presents the final architecture of the polygons intersection manager showing these steps. Results We implemented in C++ the collision detection algorithm described in this paper. Next, it is discussed one experiment using two components from a digger model, running in an AMD Athlon1600+ with 512Mb. We used one static component and a moving component. The static model has 14 surfaces and 3521 triangles. The moving component has 25 surfaces and 6205 triangles. Over the trajectory described by the moving object, there are several intersecting surfaces between the two models. Table 1 presents results AABB(P m AABB(P' n P m P' n Colliding Figure 11 - The polygons intersection manager architecture. Number ing Surface Collision Detection approach based on OAABB Total Total Time Number Number (ms AABBs Triangle Tests Tests , , , , , , ,33 Table 1 Time and overlapping tests to determine intersecting surfaces for the surface collision detection algorithm supported by the OAABB concept. Table 2 presents results obtained, when the surface collision detection manager does not use the OAABB concept, for the same objects and trajectories. On average, the use of the OAABB concept reduces the number of AABBs comparisons about forty times. It can be shown from tables 1 and 2, the contribution of the OAABB concept for the performance of the surface collision detection algorithm. It allows the determination of the intersecting surfaces, about thirty times faster on average.

7 Number ing Surface Collision Detection approach without OAABB Total Total Time Number Number (ms AABBs Triangle Tests Tests Table 2 Timing to determine intersecting surfaces in a straightforward approach. In this case, the OAABB concept is not used. We also compare results from table 1 with the RAPID [7] collision detection toolkit in table 3, for the same objects and trajectories. We use RAPID for comparison, since this approach presents good performance and functionality [11], when compared with other publicly available toolkits for collision detection. However, we remember that the RAPID collision detection toolkit determines intersecting polygons. Rapid Number Total Number Total Number Time (ms ing Triangles OBBs Tests Triangle Tests Table 3 Time and number of comparisons to determine intersecting triangles using Rapid. From tables 1 and 3, we can see that our approach is on average fifteen times faster than RAPID. The surface collision detection presented, determines intersecting surfaces, taking advantage of the scene graph structure available from the CAD model. For the simulation of maintenance operations, the application needs to know the intersecting surfaces. Two surfaces intersect if there is one pair of intersecting triangles. The use of the OAABBs, at both the object and surface levels, helps in reducing the number of axis-aligned bounding boxes and triangle tests. On average the RAPID executes three and an half more OBB tests than the surface collision detection approach executes AABBs. In this case, the OBB tests are about thirty times more expensive than AABBs comparisons [11]. Again, RAPID executes, on average, about thirty times more triangle intersecting tests than the surface collision detection algorithm described. This explains the better performance achieved by the surface collison detection algorithm presented in this paper. Conclusions and Future Work The main contribution of the present paper is the presentation of a novel collision detection algorithm, that determines precisely intersecting surfaces at interactive rates, between 3D assembly models in virtual prototype environments. We implemented this algorithm in C++. We also present our view about the development of a unified virtual prototyping environment at the Center for Virtual Environments at the University of Salford. The collision detection manager plays an important role in this framework. We identify requirements for a collision detection manager to assist assembly and maintenance operations, in a virtual prototyping environment. Current virtual prototype environments base the collision detection manager on bounding volumes or on polygonal models. The available surface data from the CAD model is not used. The novel collision detection algorithm presented in this paper determines precisely intersecting surfaces. It uses the surface knowledge available from the CAD model to improve performance and determines intersecting surfaces interactively. This knowledge about the intersecting surfaces can be used, more effectively, by the constraint-based geometric manager, in the automatic recognition of geometric constraints during user interaction in maintenance simulations. In this paper, it is also introduced the novel concept of overlapping axis-aligned bounding boxes OAABB for improving the overall performance. A straightforward collision detection algorithm is of complexity O(n 2. The use of the OAABB concept, at both the object and surface level, can significantly improve performance. We showed that the surface collision detection implementation has good performance and compares favourable to publicly available collision detection algorithms. We are planning to integrate a R-tree spatial partitioning tree, to organize the object geometry in the 3D space, to improve performance furthermore and test it in large scene graphs. Acknowledgements Mauro Figueiredo is being supported by FSE and PRODEP III program project reference 5.3/ALG/ /01.

8 References [1] Sá, A. G., and Zachmann, G. (1999. Virtual reality as a tool for verification of assembly and maintenance processes. Computers & Graphics, Vol. 23, No. 3, pp [2] Fernando, T, Marcelino, L, Wimalaratne, P. (2001 Constraint-based Immersive Virtual Environment for Supporting Assembly and Maintenance Tasks, HCII 2001, New Orleans, Vol.1, pp [3] Pratt, M. J. (1995, Virtual prototypes and product models in mechanical engineering. In J. Rix, S. Haas & J. Teixeira (Eds., Virtual prototyping virtual environments and the product design process, pp. 113 [4] Loock, A., and Schömer, E. (2001 A Virtual Environment for Interactive Assembly Simulation: From Rigid Bodies to Deformable Cables. In 5 th World Multiconference on Systemics, Cybernetics and Informatics (SCI'01, Vol. 3 (Virtual Engineering and Emergent Computing, pp [5] Wimalaratne, P. (2002, Constraint-based functional virtual prototyping for assembly simulation. PhD thesis, University of Salford, Salford, UK. [6] Cohen, J., Lin, M., Manocha, D. and Ponamgi, K. (1995. I-COLLIDE: An Interactive and Exact Collision Detection System for Large-Scale Environments, In Proceedings of ACM Int. 3D Graphics Conference, vol. 1, pp [7] Gottschalk, S., Lin, M. C. and Manocha, D. (1996. Obb-tree: A hierarchical structure for rapid interference detection, In Proc. of ACM Siggraph'96, pp [8] Hudson, T. C., Lin, M. C., Cohen, J., Gottschalk, S. and Manocha, D. (1997. V-COLLIDE: Accelerated Collision Detection for VRML, In Proc. of VRML, pp [9] Van Der Bergen, G. (1997. Efficient Collision Detection of Complex Deformable Models using AABB Trees, In Journal of Graphics Tools, 2, 4, pp [10] Klosowski, J., Held, M., Mitchell, J., Sowizral, H. and Zikan, K. (1998. Efficient Collision Detection using Bounding Volume Hierarchies of k-dops, IEEE Trans. On Visualization and Computer Graphics, 4, 1, pp [11] Figueiredo, M., Marcelino, L., Fernando, T. (2002 A Survey on Collision Detection Techniques for Virtual Environments. In Proc. of V Symposium in Virtual Reality, Brasil, pp [12] Munlin, M. (1995, Interactive assembly modeling within a virtual environment. PhD thesis, University of Leeds, Leeds, UK. [13] Wieland, F., Carnes, D. and Schultz, G. (2001 Using Quad Trees for Parallelizing Conflict Detection in a Sequencial Simulation. In Proc. of the 15th Workshop on Parallel and Distributed Simulation, pp [14] Lin, M. C. and Gottschalk, S. (1998 Collision Detection between Geometric Models: A Survey, In Proc. of IMA Conference on Mathematics of (San Diego (CA, vol. 1, pp Biography Mauro Figueiredo is Professor Adjunto at the University of Algarve, Portugal. He is a PhD student in Computer Science at the University of Salford, with research interests in collision detection for assisting assembly and maintenance operations in virtual prototyping environments. Figueiredo received his degree in Computer Science from the University of Coimbra in 1990 and his MS in Industrial Automation from University of Coimbra in Prof. Fernando is the Head of the Virtual Prototyping Research Group and he is also the Director of the North West Research Centre for Advanced Virtual Prototyping. His research interests are in constraintbased assembly modelling, maintenance simulation, distributed virtual engineering environments and multi-sensory interfaces..