Loeiz Glondu

Efficient collision detection for brittle fracture

In complex scenes with many objects, collision detection plays a key role in the simulation performance. This is particularly true for fracture simulation, where multiple new objects are dynamically created. In this paper, we present novel algorithms and data structures for collision detection in real-time brittle fracture simulations. We build on a combination of well-known efficient data structures, namely distance fields and sphere trees, making our algorithm easy to integrate on existing simulation engines. We propose novel methods to construct these data structures, such that they can be efficiently updated upon fracture events and integrated in a simple yet effective self-adapting contact selection algorithm. Altogether, we drastically reduce the cost of both collision detection and collision response. We have evaluated our global solution for collision detection on challenging scenarios, achieving high frame rates suited for hard real-time applications such as video games or haptics. Our solution opens promising perspectives for complex brittle fracture simulations involving many dynamically created objects.

Example-Based Fractured Appearance

A common weathering effect is the appearance of cracks due to material fractures. Previous exemplar‐based aging and weathering methods have either reused images or sought to replicate observed patterns exactly. We introduce a new approach to exemplar‐based modeling that creates weathered patterns on synthetic objects by matching the statistics of fracture patterns in a photograph. We present a user study to determine which statistics are correlated to visual similarity and how they are perceived by the user. We then describe a revised physically‐based fracture model capable of producing a wide range of crack patterns at interactive rates. We demonstrate how a Bayesian optimization method can determine the parameters of this model so it can produce a pattern with the same key statistics as an exemplar. Finally, we present results using our approach and various exemplars to produce a variety of fracture effects in synthetic renderings of complex environments. The speed of the fracture simulation allows interactive previews of the fractured results and its application on large scale environments.

Combining brain-computer interfaces and haptics: detecting mental workload to adapt haptic assistance

In this paper we introduce the combined use of Brain-Computer Interfaces (BCI) and Haptic interfaces. We propose to adapt haptic guides based on the mental activity measured by a BCI system. This novel approach is illustrated within a proof-of-concept system: haptic guides are toggled during a path-following task thanks to a mental workload index provided by a BCI. The aim of this system is to provide haptic assistance only when the users brain activity reflects a high mental workload. A user study conducted with 8 participants shows that our proof-of-concept is operational and exploitable. Results show that activation of haptic guides occurs in the most difficult part of the path-following task. Moreover it allows to increase task performance by 53% by activating assistance only 59% of the time. Taken together, these results suggest that BCI could be used to determine when the user needs assistance during haptic interaction and to enable haptic guides accordingly.

EVALUATION OF PHYSICAL SIMULATION LIBRARIES FOR HAPTIC RENDERING OF CONTACTS BETWEEN RIGID BODIES

Haptic rendering has opened a new range of virtual reality applications, enabling a human user to interact with a virtual world using the sense of touch. This kind of interaction enables to enhance applications such as computer-assisted design, where 3D manipulations are part of the system. However, building an application with an accurate haptic feedback is still challenging, especially for interactions between rigid bodies, where stiff contacts can only be displayed with a high simulation frequency. This paper presents the possibilities of implementation of a modular haptic display system that relies on two main components: a physical simulation part and a haptic rendering part. For that purpose, we define a generic coupling approach that enables to perform haptic rendering using admittance haptic devices, through a scaling interface that cleanly separates the physical simulation and the haptic rendering system of units. Four physical simulation libraries are evaluated with respect to haptic rendering quality criteria, based on their behavior in four discriminant test cases. We show that the proposed approach leads to a modular, generic and stable haptic application.

Precomputed Shape Database for Real-Time Physically-Based Simulation

Adding dynamically physical properties to virtual objects can not generally be handled in real-time during a simulation. In this paper, we propose a method for handling the real-time physical simulations of arbitrary objects that are represented by their surface mesh. Our method is based on a database in which physical data are stored for a wide variety of objects. When a query object needs to be physically simulated in the virtual world, a similarity search is performed in the database and the associate physical data are then extracted. We propose and compare three different similarity search methods that fit with our real-time needs. We demonstrate our approach for the simulations of different physical phenomena such as fracture or deformations. Our results show that our method has a great potential for the physical simulation of objects represented by their surface meshes in interactive applications.

A Sub-world Coupling Scheme for Haptic Rendering of Physically-based Rigid Bodies Simulation

In the virtual reality context, the use of haptic rendering as an additional se nsory modality significantly improves the degree of realism of virtual worlds. The physical realism of the intera ction between the user and the objects of the virtual world is particularly important when dealing with contact or collis ion between rigid objects as, for example, in assembly tasks. The high frequency rates required for smoo th manipulations are often difficult to reach, in particular for rigid bodies simulations. Hence, we propose a new coupling scheme based on a dynamic subset of the virtual world, a localized Haptic Sub-World, running at a higher freq uency than the rest of the virtual world. This Sub-World, located around the virtual object manipulated by the user , is synchronized with the virtual world through a dynamic analysis of the interface between the two subsets. Using th is coupling scheme in our software environment, we are able to achieve high frequency haptic rendering usin g sophisticated simulation methods on virtual worlds with a large number of rigid bodies.