The exploration of complex walkthrough models is often a difficult task due to the presence of densely occluded regions which pose a serious challenge to online navigation. In this paper we address the problem of algorithmic generation of exploration paths for complex walkthrough models. We present a characterization of suitable properties for camera paths and we discuss an efficient algorithm for computing them with little or no user intervention. Our approach is based on identifying the free-space structure of the scene (represented by a cell and portal graph) and an entropy-based measure of the relevance of a view-point. This metric is key for deciding which cells have to be visited and for computing critical way-points inside each cell. Several results on different model categories are presented and discussed.

Virtual Reality (VR) is being integrated into many different areas of our lives, from industrial engineering to video-games, and also including teaching and education. We have several examples where VR has been used to engage students and facilitate their 3D spatial understanding, but can VR help also teachers? What are the benefits teachers can obtain on using VR applications? In this paper we present an application (VR4Health) designed to allow students to directly inspect 3D models of several human organs by using Virtual Reality systems. The application is designed to be used in an HMD device autonomously as a self-learning tool and also reports information to teachers in order that he/she becomes aware of what the students do and can redirect his/her work to the concrete necessities of the student. We evaluate both the students' and the teachers' perception by doing an experiment and asking them to fill-in a questionnaire at the end of the experiment.

Relief impostors have been proposed as a compact and high-quality representation for high-frequency detail in 3D models. In this paper we propose an algorithm to represent a complex object through the combination of a reduced set of relief maps. These relief maps can be rendered with very few artifacts and no apparent deformation from any view direction. We present an efficient algorithm to optimize the set of viewing planes supporting the relief maps, and an image-space metric to select a sufficient subset of relief maps for each view direction. Selected maps (typically three) are rendered based on the well-known ray-height-field intersection algorithm implemented on the GPU. We discuss several strategies to merge overlapping relief maps while minimizing sampling artifacts and to reduce extra texture requirements. We show that our representation can maintain the geometry and the silhouette of a large class of complex shapes with no limit in the viewing direction. Since the rendering cost is output sensitive, our representation can be used to build a hierarchical model of a 3D scene. Figure 1: Several relief maps are combined to provide an impostor set that can be rendered from arbitrary directions.

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Abstract. We characterize the feature superset of Collaborative Virtual Reality Environments (CVREs) out of existing implementations, and derive a novel component framework for transforming standalone VR tools into full-fledged multithreaded collaborative environments. The contributions of our approach rely on cost-effective techniques for loading graphics rendering, user interaction and network communications software components into separate threads, with a top thread for session collaboration. The framework recasts VR tools under a scalable peer-to-peer topology for scene sharing, callback hooks for event broadcasting and multicamera perspectives of avatar interaction. We validate the framework by applying it to our own ALICE VR Navigator. Experimental results show good performance of our approach in the collaborative inspection of complex models.

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