René Caubet

A new object-order ray-casting algorithm

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.

Discrete Ray-Tracing of Huge Voxel Spaces

The quality of images produced by Discrete Ray‐Tracing voxel spaces is highly dependent on 3d grid resolution. The huge amount of memory needed to store such grids often discards discrete Ray‐Tracing as a practical visualization algorithm. The use of an octree can drastically change this when most of space is empty, as such is the case in most scenes.

EXTRUSION OF 1D IMPLICIT PROFILES: THEORY AND FIRST APPLICATION

This paper presents a new interpretation of the general definition of the binary blending operator of implicit modeling. Instead of considering the operator as a composition of potential functions or as a function defined in the combined primitives metric, we propose to consider it as an implicit curve extruded in an implicit extrusion field. An implicit extrusion field is a 2D space for which each coordinate is a potential field. The study of general concepts around implicit extrusion field allows us to introduce theoretical notion of free-form blending controlled point-by-point by the user. Through the use of functional interpolation functions, we propose modeling tools to create, sculpt or combine implicit primitives by extrusion of a profile in an implicit extrusion field.

An Extended Radiosity Using Parallel Ray-Traced Specular Transfers

The realism in image synthesis needs complex illumination models. In this paper, our goal is to describe a parallel extended radiosity method with general reflectance functions. This approach will allow us to produce realistic images. At first, we analyse existing extended radiosity methods to explain the energy transfer principles and how to compute them. Then we study theoretical frameworks on radiance and luminance transfers in a close environment to deduce a progressive extended radiosity method with parallel ray-traced specular transfers. Then we describe our implementation of this method in the VOXAR machine, parallel architecture dedicated to the ray-tracing algorithm.

Visualization of Isosurfaces with Parametric Cubes

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.

Interactive constraint system for solid modeling objects

The interaction of mechanisms applications presents a challenging domain for research in constraint-based systems. In these applications several requirements must be solved. Time consuming and complex tasks must take advantage of every computational opportunity to improve performance. Moreover, the constraints solver must give a rapid solution even in critical situations such as under-constraints, over-constraints and cyclic constraints problems. In this paper, we present a geometric constraint system named LinkEdit that provides an interactive tool to construct objects from rigid primitives and constrain them by several constraints types. In LinkEdit system, internal and external constraints are integrated as a new paradigm for constraint definition and the constraint solver is designed to handle the previous requirements, by combining local propagation and propagation of degrees of freedom techniques.

Multi-user interactions in the context of concurrent virtual world modelling

Distributed virtual reality, thanks to newly proposed paradigms, offers interesting perspectives to virtual world modelling. Our main interests are in applications which allow users to edit and deform existing shapes. This paper presents a concurrent virtual world modelling application based on those ideas. Herein is shown how concrete manipulations of tools (such as a hammer) are transformed into free form deformations of existing shapes. We also present a first implementation based on VIPER (Virtuality Programming EnviRonment) a generic distributed virtual reality development platform.

A 4D Ray Tracing

We are going to present a survey of techniques using temporal coherence in between frames to render animation sequences with ray tracing. A new method using temporal coherence in the ray space (lightpath of rays) is proposed. The goal of this technique is to factorize intersection and illumination calculations over the frames of the sequence. An optical event springing out many times in the sequence is computed once. The method is based upon 4D intersection calculations between temporal rays and moving objects. At the end of this paper, we present measurements showing the number of rays we need not calculate with our solution. These results come from simulating the algorithm behavior through a graphic and statistic ray analyser tool.

Modelling with constraints: a bibliographical survey

Nowadays, constraint solvers play a fundamental role in many graphical applications, including geometrical and mechanical CAD systems, layouts, user interfaces and animation. These applications use constraints to conveniently describe the relations between objects. Constraints are automatically maintained and satisfied by a constraint solver. So, numerical and tedious tasks are left to the solver and the designer can concentrate on the design process. In this paper, we present the concepts of constraints and constraint solvers. We classify the principal resolution methods, giving their drawbacks and shortcomings. We also examine different application domains using constraint solvers.

Accelerating volume rendering with quantized voxels

We present here a new algorithm for accelerating volume rendering with an orthographic projection. Because volume rendering handles huge data sets, a reduction in the computational cost of voxel projection is required to obtain interactive volume rendering. We satisfy this issue by using the possibilities of orthographic projection that allows the quantization of voxel positions by subdividing the pixels. The same projection properties are given for all the voxels with the center falling within the same pixel subdivision. In contrast with classical algorithms that require several instructions to compute either the next traversed voxel or the next rasterized pixel, our method needs only one addition instruction and one addressing instruction that is sufficient to determine one projected pixel. Splatting can also have a decisive advantage of it. Our algorithm is well suited for low-end platforms when no hardware acceleration is available. Experimental results show that our rendering rate is better than other existing methods. This algorithm might allow obtaining real-time volume rendering on conventional computers soon.