Marta Fairén

Way‐Finder: guided tours through complex walkthrough models

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.

Omni‐directional Relief Impostors

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.

Enhancing collaboration in virtual reality applications

We derive a complete component framework for transforming standalone virtual reality (VR) applications into full-fledged multithreaded collaborative virtual reality environments (CVREs), after characterizing existing implementations into a feature-rich superset. Our main contribution is placing over the existing VR tool a very concise and extensible class framework as an add-on component that provides emerging collaboration features. The enhancements include: a scalable arbitrated peer-to-peer topology for scene sharing; multi-threaded components for graphics rendering, user interaction and network communications; a streaming message protocol for client communications; a collaborative user interface model for session handling; and interchangeable user roles with multicamera perspectives, avatar awareness and shared 3D annotations. We validate the framework by converting the existing ALICE VR Navigator into complete CVRE, with experimental results showing good performance in the collaborative inspection and manipulation of complex models.

MiniVR: a portable virtual reality system

Abstract This paper describes a new virtual reality system designed to be small enough to be totally portable. It is a semi-immersive interaction system based on a movable stereoscopic projection screen with a tracking system to capture the movement of the screen with respect to the virtual model. The system can be used for cooperative inspection of very complex computer-aided design environments, allowing very simple interaction among users and designers at distant locations.

On extending collaboration in virtual reality environments

We characterize the feature superset of collaborative virtual reality environments (CVRE) out of existing implementations, and derive a novel component framework for transforming standalone VR tools into fully fledged multi-threaded 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 the good performance of our approach in the collaborative inspection of complex models.

Simplification of Topologically Complex Assemblies

In this paper we present a new simplification approach intended for scenes containing a huge number of simple objects forming a topologically complex assembly. Our method combines appearance preservation and topology reduction by converting a 3D model to and from an intermediate octree representation. During the conversion of the input mesh into an octree, appearance attributes such as colour are stored in the octree nodes. Unlike related approaches, the inside/outside values at octree vertices are computed according to neighbourhood configuration rather than by direct sampling. This allows the reconstructed surface to span only a reduced subset of the terminal nodes of the octree (those which are classified as border nodes), thus avoiding small cracks and removing internal structures not visible from the outside. The reconstruction step of our method succeeds in preserving the appearance of most of the scene objects while drastically simplifying the geometry and topology.