CAGD-based computer vision

Journal ArticleThree-dimensional model-based computer vision uses geometric models of objects and sensed data to recognize objects in a scene. Likewise, Computer Aided Geometric Design (CAGD) systems are used to interactively generate three-dimensional models during the design process. Despite this similarity, there has been a dichotomy between these fields. Recently, the unification of CAGD and vision systems has become the focus of research in the context of manufacturing automation

Parallel lumigraph reconstruction

Journal ArticleThis paper presents three techniques for reconstructing Lumigraphs/ Lightfields on commercial ccNUMA parallel distributed shared memory computers. The first method is a parallel extension of the software-based method proposed in the Lightfield paper. This expands the ray/two-plane intersection test along the film plane, which effectively becomes scan conversion. The second method extends this idea by using a shear/warp factorization that accelerates rendering. The third technique runs on an SGI Reality Monster using up to eight graphics pipes and texture mapping hardware to reconstruct images. We characterize the memory access patterns exhibited using the hardware-based method and use this information to reconstruct images from a tiled UV plane. We describe a method to use quad-cubic reconstruction kernels. We analyze the memory access patterns that occur when viewing Lumigraphs. This allows us to ascertain the cost/benefit ratio of various tilings of the texture plane

Binary-swap and shear-warp volume renderer on the T3D

Journal ArticleLarge parallel machines give today's scientists the ability to compute very large simulations which may generate equally large data. Not only does having visualization tools on the parallel system allow the scientist to take advantage of the large memory to visualize the data, the processing power allows interactive manipulation of visualization parameters. We will describe a volume renderer on the T3D which allows us to take advantage of the capabilities of the Shear-Warp renderer and the Binary-Swap compositing algorithm to produce an image in sub-second times, several seconds faster than other techniques. An interactive interface using AVS through a FDDI connection is described

Model for volume lighting and modeling

Journal ArticleAbstract-Direct volume rendering is a commonly used technique in visualization applications. Many of these applications require sophisticated shading models to capture subtle lighting effects and characteristics of volumetric data and materials. For many volumes, homogeneous regions pose problems for typical gradient-based surface shading. Many common objects and natural phenomena exhibit visual quality that cannot be captured using simple lighting models or cannot be solved at interactive rates using more sophisticated methods. We present a simple yet effective interactive shading model which captures volumetric light attenuation effects that incorporates volumetric shadows, an approximation to phase functions, an approximation to forward scattering, and chromatic attenuation that provides the subtle appearance of translucency. We also present a technique for volume displacement or perturbation that allows realistic interactive modeling of high frequency detail for both real and synthetic volumetric data

CAGD-based computer vision

Journal ArticleAbstract-Three-dimensional model-based computer vision uses geometric models of objects and sensed data to recognize objects in a scene. Likewise, computer aided geometric design (CAGD) systems are used to interactively generate three-dimensional models during the design process. Despite this similarity, there has been a dichotomy between these fields. Recently, the unification of CAGD and vision systems has become the focus of research in the context of manufacturing automation

Interactive rendering and efficient querying for large multivariate seismic volumes on consumer level PCs

pre-printWe present a volume visualization method that allows interactive rendering and efficient querying of large multivariate seismic volume data on consumer level PCs. The volume rendering pipeline utilizes a virtual memory structure that supports out-of-core mul- tivariate multi-resolution data and a GPU-based ray caster that allows interactive multivariate transfer function design. A Gaussian mixture model representation is precomputed and nearly interactive querying is achieved by testing the Gaussian functions against user defined transfer functions on the GPU in the runtime. Finally, the method has been tested on a multivariate 3D seismic dataset which is larger than the size of the main memory of the testing machine

CAD-based robotics

Journal ArticleWe describe an approach which facilitates and makes explicit the organization of the knowledge necessary to map robotic system requirements onto an appropriate assembly of algorithms, processors, sensor, and actuators. In order to achieve this mapping, several kinds of knowledge are needed. In this paper, we describe a system under development which exploits the Computer Aided Design (CAD) database in order to synthesize

Non-photorealistic volume rendering using stippling techniques

Journal ArticleSimulating hand-drawn illustration techniques can succinctly express information in a manner that is communicative and informative. We present a framework for an interactive direct volume illustration system that simulates traditional stipple drawing. By combining the principles of artistic and scientific illustration, we explore several feature enhancement techniques to create effective, interactive visualizations of scientific and medical datasets. We also introduce a rendering mechanism that generates appropriate point lists at all resolutions during an automatic preprocess, and modifies rendering styles through different combinations of these feature enhancements. The new system is an effective way to interactively preview large, complex volume datasets in a concise, meaningful, and illustrative manner. Volume stippling is effective for many applications and provides a quick and efficient method to investigate volume models

Volume Ray casting with peak finding and differential sampling

Journal ArticleDirect volume rendering and isosurfacing are ubiquitous rendering techniques in scientific visualization, commonly employed in imaging 3D data from simulation and scan sources. Conventionally, these methods have been treated as separate modalities, necessitating different sampling strategies and rendering algorithms. In reality, an isosurface is a special case of a transfer function, namely a Dirac impulse at a given isovalue. However, artifact-free rendering of discrete isosurfaces in a volume rendering framework is an elusive goal, requiring either infinite sampling or smoothing of the transfer function. While preintegration approaches solve the most obvious deficiencies in handling sharp transfer functions, artifacts can still result, limiting classification. In this paper, we introduce a method for rendering such features by explicitly solving for isovalues within the volume rendering integral. In addition, we present a sampling strategy inspired by ray differentials that automatically matches the frequency of the image plane, resulting in fewer artifacts near the eye and better overall performance. These techniques exhibit clear advantages over standard uniform ray casting with and without preintegration, and allow for high-quality interactive volume rendering with sharp C0 transfer functions

Interactive isosurface ray tracing of time-varying tetrahedral volumes

Journal ArticleAbstract- We describe a system for interactively rendering isosurfaces of tetrahedral finite-element scalar fields using coherent ray tracing techniques on the CPU. By employing state-of-the art methods in polygonal ray tracing, namely aggressive packet/frustum traversal of a bounding volume hierarchy, we can accomodate large and time-varying unstructured data. In conjunction with this efficiency structure, we introduce a novel technique for intersecting ray packets with tetrahedral primitives. Ray tracing is flexible, allowing for dynamic changes in isovalue and time step, visualization of multiple isosurfaces, shadows, and depth-peeling transparency effects. The resulting system offers the intuitive simplicity of isosurfacing, guaranteed-correct visual results, and ultimately a scalable, dynamic and consistently interactive solution for visualizing unstructured volumes