Exact From-region Visibility Culling

To pre-process a scene for the purpose of visibility culling during walkthroughs it is necessary to solve visibility from all the elements of a finite partition of viewpoint space. Many conservative and approximate solutions have been developed that solve for visibility rapidly. The idealised exact solution for general 3D scenes has often been regarded as computationally intractable. Our exact algorithm for finding the visible polygons in a scene from a region is a computationally tractable pre-process that can handle scenes of the order of millions of polygons. The essence of our idea is to represent 3-D polygons and the stabbing lines connecting them in a 5-D Euclidean space derived from Plücker space and then to perform geometric subtractions of occluded lines from the set of potential stabbing lines.We have built a query architecture around this query algorithm that allows for its practical application to large scenes. We have tested the algorithm on two different types of scene: despite a large constant computational overhead, it is highly scalable, with a time dependency close to linear in the output produced

Exact from-region visibility culling

To pre-process a scene for the purpose of visibility culling during walkthroughs it is necessary to solve visibility from all the elements of a finite partition of viewpoint space. Many conservative and approximate solutions have been developed that solve for visibility rapidly. The idealised exact solution for general 3D scenes has often been regarded as computationally intractable. Our exact algorithm for finding the visible polygons in a scene from a region is a computationally tractable pre-process that can handle scenes of the order of millions of polygons. The essence of our idea is to represent 3-D polygons and the stabbing lines connecting them in a 5-D Euclidean space derived from Plücker space and then to perform geometric subtractions of occluded lines from the set of potential stabbing lines.We have built a query architecture around this query algorithm that allows for its practical application to large scenes. We have tested the algorithm on two different types of scene: despite a large constant computational overhead, it is highly scalable, with a time dependency close to linear in the output produced

A Framework for n-dimension Visibility Calculation

4 pagesVisibility computation is a fundamental task in computer graphics, as in many other scientific domains. While it is well understood in two dimensions, this does not remain true in high dimensional spaces. Using Grassmann Algebra, we propose a framework for solving visibility problems in any n-dimensional spaces, for n ≥ 2. Our presentation recalls the problem statement, in two and three dimensions. Then, we formalize the space of n-dimensional lines. Finally, we show how this leads to a global framework for visibility computations, giving an example of use with exact soft shadows

Some Considerations about Geometric Algebras in relation with Visibility in Computer Graphics

We give some considerations about the use of geometric algebras in the context of visibility, showing some advantages and disadvantages for their use as the underlying framework. We emphasize the use of conformal geometric algebra since, among other reasons, it allows us to study easily the visibility for flat varieties and, due to the same algebraic expression of hyper-spheres and linear varieties, the results might be generalized to non-flat objects

Emergency crowd simulation for outdoor environments

Cataloged from PDF version of article.We simulate virtual crowds in emergency situations caused by an incident, such as a fire, an explosion, or a terrorist attack. We use a continuum dynamics-based approach to simulate the escaping crowd, which produces more efficient simulations than the agent-based approaches. Only the close proximity of the incident region, which includes the crowd affected by the incident, is simulated. We use a model-based rendering approach where a polygonal mesh is rendered for each agent according to the agent's skeletal motion. To speed up the animation and visualization, we employ an offline occlusion culling technique. We animate and render a pedestrian model only if it is visible according to the static visibility information computed. In the pre-processing stage, the navigable area is decomposed into a grid of cells and the from-region visibility of these cells is computed with the help of hardware occlusion queries. (C) 2009 Elsevier Ltd. All rights reserved

Cartes de photons et visibilité

Les méthodes de simulation d'éclairage par tracé de photons sont souvent utilisées pour leur simplicité et leur versatilité. Les deux étapes classiques de ces approches sont : (i) les calculs d'inter-réflexions lumineuses, indépendantes du point de vue, correspondant à des suivis de chemins lumineux dont les impacts sur les surfaces de la scène sont stockés sous forme de cartes de photons ; (ii) l'exploitation des cartes de photons pour produire une ou plusieurs images de l'environnement virtuel. La première phase repose exclusivement sur des méthodes de Monte-Carlo ; la seconde requiert au moins une estimation de densité pour le calcul d'éclairement. Malheureusement, le tracé de photons est également connu pour les différents biais produits lors de l'estimation de densité des photons pour le calcul de l'éclairement en un point. Ce rapport montre pourquoi la visibilité est un élément fondamental lors de l'estimation de densité ; nous proposons de la prendre en compte de manière précise pour réduire ou supprimer certains biais. Nos résultats mettent en évidence l'importance de la visibilité dans la qualité des images produites

Lazy visibility evaluation for exact soft shadows

International audienceThis report presents a novel approach to compute high quality and alias-free soft shadows using exact visibility computations. This work relies on a theoritical framework allowing to group lines according to the geometry they intersect. From this study, we derive a new algorithm encoding lazily the visibility from a polygon. Contrary to previous works on from-polygon visibility, our approach is very robust and straightforward to implement. We apply this algorithm to solve exactly and efficiently the visibility of an area light source from any point in a scene. As a consequence, results are not sensitive to noise, contrary to soft shadows methods based on area light source sampling. We demonstrate the reliability of our approach on different scenes and configurations

Lazy visibility evaluation for exact soft shadows

Présentation invitée de l'article du même nom publié en 2012 dans la revue Computer Graphics Forum.International audienceThis paper presents a novel approach to compute high quality and noise-free soft shadows using exact visibility computations. This work relies on a theoretical framework allowing to group lines according to the geometry they intersect. From this study, we derive a new algorithm encoding lazily the visibility from a polygon. Contrary to previous works on from-polygon visibility, our approach is very robust and straightforward to implement. We apply this algorithm to solve exactly and efficiently the visibility of an area light source from any point in a scene. As a consequence, results are not sensitive to noise, contrary to soft shadows methods based on area light source sampling. We demonstrate the reliability of our approach on different scenes and configurations

Computing axes of rotation for 4-axis CNC milling machine by calculating global visibility map from slice geometry

This thesis presents a new method to compute a global visibility map (GVM) in order to determine feasible axes of rotation for 4-axis CNC machining. The choice of the 4th-axis is very important because it directly determines the critical manufacturing components; visibility, accessibility and machinability of the part. As opposed to the considerable work in GVM computation, this thesis proposes an innovative approximation approach to compute GVM by utilizing slice geometry. One advantage of the method is that it is feature-free, thus avoiding feature extraction and identification. In addition, the method is computationally efficient, and can be easily parallelized in order to vastly increase speed. In this thesis, we further present a full implementation of the approach as a critical function in an automated process planning system for rapid prototyping