Volumetric ray tracing

ACM Siggraph Computer Graphics, 1984

This paper presents new algorithms to trace objects represented by densities within a volume grid, e.g. clouds, fog, flames, dust, particle systems. We develop the light scattering equations, discuss previous methods of solution, and present a new approximate solution to the full three-dimensional radiative scattering problem suitable for use in computer graphics. Additionally we review dynamical models for clouds used to make an animated movie.

1995

In this paper we present an acceleration method for volumetric ray tracing which utilizes standard graphics hardware without compromising image accuracy. The graphics hardware is employed to ident@ those segments of each ray that could possibly contribute to the jinal image. A volumetric ray tracing algorithm is then used to compute the$nal image, traversing only the identi$ed segments of the rays. This technique can be used to render volumetric isosurfaces as well as translucent volumes. In addition, this method can accelerate the traversal of shadow rays when performing recursive ray tracing.

ACM Transactions on Graphics, 2005

We present a new, fast algorithm for rendering physically-based soft shadows in ray tracing-based renderers. Our method replaces the hundreds of shadow rays commonly used in stochastic ray tracers with a single shadow ray and a local reconstruction of the visibility function. Compared to tracing the shadow rays, our algorithm produces exactly the same image while executing one to two orders of magnitude faster in the test scenes used. Our first contribution is a two-stage method for quickly determining the silhouette edges that overlap an area light source, as seen from the point to be shaded. Secondly, we show that these partial silhouettes of occluders, along with a single shadow ray, are sufficient for reconstructing the visibility function between the point and the light source.

Computer Graphics Forum, 1998

This paper presents a method taking global illumination into account in a ray tracing environment. A vector approach is introduced, which allows to deal with all the types of light paths and the directional properties of materials. Three types of vectors are defined: Direct Light Vectors associated to light sources, Indirect Light Vectors which correspond to light having been diffusely reflected at least once and Caustic Light Vectors which are associated to light rays emitted by sources and reflected and/or transmitted by specular surfaces. These vectors are estimated at a small number of points in the scene. A weighted interpolation between known values allows to reconstruct these vectors for the other points, with the help of a gradient computation for the indirect component. This approach also allows to take uniform area light sources (spherical, rectangular and circular) into account for all the types of vectors. Computed images are thus more accurate and no discretizing of the geometry of the scene is needed.

Field Guide to Astronomical Instrumentation

We describe a methodology for implementing a ray tracer which provides both a convenient testbed for developing new algorithms and a way to exploit the growing number of acceleration techniques. These bene ts are a natural consequence of a collection of data abstractions called the ray tracing kernel. By de ning an object in a broad sense, the kernel allows a single abstraction to encapsulate a wide spectrum of concepts including geometric primitives, acceleration techniques, CSG operators, and object transformations. Through hierarchical nesting of instances of these objects we are able to construct and eciently render complex environments.

PLoS ONE, 2012

The field of volume visualization has undergone rapid development during the past years, both due to advances in suitable computing hardware and due to the increasing availability of large volume datasets. Recent work has focused on increasing the visual realism in Direct Volume Rendering (DVR) by integrating a number of visually plausible but often effect-specific rendering techniques, for instance modeling of light occlusion and depth of field. Besides yielding more attractive renderings, especially the more realistic lighting has a positive effect on perceptual tasks. Although these new rendering techniques yield impressive results, they exhibit limitations in terms of their exibility and their performance. Monte Carlo ray tracing (MCRT), coupled with physically based light transport, is the de-facto standard for synthesizing highly realistic images in the graphics domain, although usually not from volumetric data. Due to the stochastic sampling of MCRT algorithms, numerous effects can be achieved in a relatively straight-forward fashion. For this reason, we have developed a practical framework that applies MCRT techniques also to direct volume rendering (DVR). With this work, we demonstrate that a host of realistic effects, including physically based lighting, can be simulated in a generic and flexible fashion, leading to interactive DVR with improved realism. In the hope that this improved approach to DVR will see more use in practice, we have made available our framework under a permissive open source license.

IEEE Transactions on Visualization and Computer Graphics, 2012

We present an algorithm that enables real-time dynamic shading in direct volume rendering using general lighting, including directional lights, point lights and environment maps. real-time performance is achieved by encoding local and global volumetric visibility using spherical harmonic (SH) basis functions stored in an efficient multi-resolution grid over the extent of the volume. Our method enables high frequency shadows in the spatial domain, but is limited to a low frequency approximation of visibility and illumination in the angular domain. In a first pass, Level Of Detail (LOD) selection in the grid is based on the current transfer function setting. This enables rapid on-line computation and SH projection of the local spherical distribution of visibility information. Using a piecewise integration of the SH coefficients over the local regions, the global visibility within the volume is then computed. By representing the light sources using their SH projections, the integral over lighting, visibility and isotropic phase functions can be efficiently computed during rendering. The utility of our method is demonstrated in several examples showing the generality and interactive performance of the approach.

Computer Graphics Forum, 2013

Interactive volume rendering in its standard formulation has become an increasingly important tool in many application domains. In recent years several advanced volumetric illumination techniques to be used in interactive scenarios have been proposed. These techniques claim to have perceptual benefits as well as being capable of producing more realistic volume rendered images. Naturally, they cover a wide spectrum of illumination effects, including varying shading and scattering effects. In this survey, we review and classify the existing techniques for advanced volumetric illumination. The classification will be conducted based on their technical realization, their performance behavior as well as their perceptual capabilities. Based on the limitations revealed in this review, we will define future challenges in the area of interactive advanced volumetric illumination.

Intelligent Computer Graphics …, 2010

In this paper we present a novel real-time algorithm to compute the global illumination of dynamic scenes with arbitrarily complex dynamic illumination. We use a virtual point light (VPL) illumination model on the volume representation of the scene. Unlike other dynamic VPL-based real-time approaches, our method handles occlusion (shadowing and masking) caused by the interference of geometry and is able to estimate diffuse inter-reflections from multiple light bounces.

1990

We provide a general technique for all ray tracing space subdivision methods to perform what we term as "Approximate Ra.y Tracing." An implementation of the Approximate Ray Tracing called the Approximate Slicing Extent Technique or ASET is provided. ASET checks only one ray-polygon intersection per cell along the path of the ray. All other ray-object intersections are eliminated. While the benefits of standard art>a subdivision techniques have proven to be fairly optimal, our experiments have shown an average of fifteen to fifty percent reduction in the time required to ray trace approximate images. Time savings are expected to be greater when more complex scenes are rendered. Irrespective of the scene complexity, ASET adds only a constant amount of memory overhead.