International audience

Abstract We propose a versatile pipeline to render B‐Rep models interactively, precisely and without rendering‐related artifacts such as cracks. Our rendering method is based on dynamic surface evaluation using both tesselation and ray‐casting, and direct GPU surface trimming. An initial rendering of the scene is performed using dynamic tesselation. The algorithm we propose reliably detects then fills up cracks in the rendered image. Crack detection works in image space, using depth information, while crack‐filling is either achieved in image space using a simple classification process, or performed in object space through selective ray‐casting. The crack filling method can be dynamically changed at runtime. Our image space crack filling approach has a limited runtime cost and enables high quality, real‐time navigation. Our higher quality, object space approach results in a rendering of similar quality than full‐scene ray‐casting, but is 2 to 6 times faster, can be used during navigation and provides accurate, reliable rendering. Integration of our work with existing tesselation‐based rendering engines is straightforward.

This research work is carried out in the framework of a project focusing on the future of aeronautical maintenance. One of our main objectives is to localize continuously technicians in relation to the aircraft on which they intervene during maintenance session. This module will be part of a context-aware application that will deliver several services to maintainers. The challenge is hard, the expected precision is around a centimeter and constraints are numerous. As for examples, the system must work inside and outside a hangar, inside and outside the aircraft, whatever the hangar configuration, the weather, the luminosity are. This paper presents the early stages of our research methodology. It first provides initial steps that were dedicated to a study of the operational context and a discussion of the results of a state of art of available technologies for localization. They allowed us to concentrate our choices on a Hybrid Localization System (HLS) combining an Inertial Measurement Unit (IMU), a 3D model of the aircraft and a third technology that will be integrated later (optical or radio wave). Next, this document depicts methods that have been implemented and tested. Depending on the way covered by the technician during the maintenance session, the obtained error rate is around 5-10%. The 3D registration offers an interesting gain inside the aircraft or in the vicinity of binding elements. In this difficult context, the research path taken to design the HLS looks already promising. Localization will be improved when the vision module, on which we are still working, will be integrated.

Abstract This paper presents an experimental feedback on a serious game dedicated to strengthening programming skills. This serious game, called Prog&Play, is built on an open source real‐time strategy game. Its goal is to be compatible with different students, teachers and institutions. We based its evaluation on an iterative process that allows to implement the game and carry out experimentations in several contexts. Through this assessment, we define a framework which has been tested by third parties and we analyse both positive and negative points to improve the project. Evaluation is indeed beneficial and enables you to establish communication about the implemented practices.

Distributed virtual environments (DVEs) should provide a quick feedback of users' interactions as well as a coherent view of the shared world. Nowadays, DVEs are scaling in complexity and in number of participants, which increases message exchange. This increase consumes processing power and bandwidth, and thus limits interactivity, consistency and scalability. To reduce the amount of message exchange, DVEs systems use various filtering techniques. Among these, interest management techniques filter messages according to users' interests in the world. In this paper, we present ASSET, a DVE system that uses a multicast and multi-server interest management filtering technique. It is aimed to scale well while maintaining interactivity, coherency and simplicity.

Development of mixed reality systems is almost always following an ad-hoc process. The development cycle often turns out to be highly expensive and time consuming. This paper presents a new prototyping approach: a combination of model-based design and simulation based prototyping.

Many direct volume rendering algorithms have been proposed during the last decade to render 256/sup 3/ voxels interactively. However a lot of limitations are inherent to all of them, like low-quality images, a small viewport size or a fixed classification. In contrast, interactive high quality algorithms are still a challenge nowadays. We introduce here an efficient and accurate technique called object-order ray-casting that can achieve up to 10 fps on current workstations. Like usual ray-casting, colors and opacities are evenly sampled along the ray, but now within a new object-order algorithm. Thus, it allows to combine the main advantages of both worlds in term of speed and quality. We also describe an efficient hidden volume removal technique to compensate for the loss of early ray termination.

To render images from volume datasets, an interpolation method also called reconstruction is needed. The level of details of the resultant image closely depends on the filter used for reconstruction. We propose here a new filter producing C1 continue surfaces. The provided image quality is better than current high-quality algorithms, like splatting or trilinear raycasting, where tiny details are often eliminated. In contrast with other studied high quality filters that are practically unusable, our algorithm has been implemented interactively on a modest platform thanks to an efficient implementation using parametric cubes. We also demonstrate the interest of a min-max octree in the visualization of isosurfaces interactively thresholded.

Abstract: The radiosity method is one of the most popular rendering algorithms. It allows to simulate interreflections of light accurately between surfaces as energy transfers are well designed. However, this algorithm and its derivatives need to break scenes into a relatively large number of small elements to approximate the illumination function. Even with a very large number of elements, not all the illumination effects can be simulated. In fact, there are always artefacts when modelling sharp shadows, besides shadows falling between mesh vertices can be missed entirely. To reduce the computational cost of such methods and to increase the accuracy of the radiosity solution, adaptive mesh generation is well suited. In this paper, we present a ray‐tracing based algorithm for adaptive mesh generation which resolves all the illumination problems without lengthening computation time too much. This method allows a small number of initial elements and increases element density in critical locations while solving the illumination problem.