Abstract—In this paper, we present a framework for high quality splatting based on elliptical Gaussian kernels. To avoid aliasing artifacts, we introduce the concept of a resampling filter, combining a reconstruction kernel with a low-pass filter. Because of the similarity to Heckbert’s EWA (elliptical weighted average) filter for texture mapping, we call our technique EWA splatting. Our framework allows us to derive EWA splat primitives for volume data and for point-sampled surface data. It provides high image quality without aliasing artifacts or excessive blurring for volume data and, additionally, features anisotropic texture filtering for point-sampled surfaces. It also handles nonspherical volume kernels efficiently; hence, it is suitable for regular, rectilinear, and irregular volume datasets. Moreover, our framework introduces a novel approach to compute the footprint function, facilitating efficient perspective projection of arbitrary elliptical kernels at very little additional cost. Finally, we show that EWA volume reconstruction kernels can be reduced to surface reconstruction kernels. This makes our splat primitive universal in rendering surface and volume data. Index Terms—Rendering systems, volume rendering, texture mapping, splatting, antialiasing. 1

In this paper we give I/O-optimal techniques for the extraction of isosurfaces from volumetric data, by a novel application of the I/Ooptimal interval tree of Arge and Vitter. The main idea is to preprocess the dataset once and for all to build an efficient search structure in disk, and then each time we want to extract an isosurface, we perform an output-sensitive query on the search structure to retrieve only those active cells that are intersected by the isosurface. During the query operation, only two blocks of main memory space are needed, and only those active cells are brought into the main memory, plus some negligible overhead of disk accesses. This implies that we can efficiently visualize very large datasets on workstations with just enough main memory to hold the isosurfaces themselves. The implementation is delicate but not complicated. We give the first implementation of the I/O-optimal interval tree, and also implement our methods as an I/O filter for Vtk's isosurface ext...

We present a simple,robust, and practical method for object simplification for applications where gradual elimination of high frequency details is desired. This is accomplished by converting an object into multi-resolution volume rastersusing a controlled filtering and sampling technique.Amultiresolution triangle-mesh hierarchycan then be generated by applying the Marching Cubes algorithm. We f urther propose an adaptive surface generation algorithm to reduce the number of triangles generated by the standardMarching Cubes. Our method simplifies the topology of objects in a controlled fashion. In addition, at eachlevel of detail, multi-layered meshes can be used for an efficient antialiased rendering.

In this paper, using certain conformal mappings from uniformization theory, we give an explicit method for flattening the brain surface in a way which preserves angles. From a triangulated surface representation of the cortex, we indicate how the procedure may be implemented using finite elements. Further, we show how the geometry of the brain surface may be studied using this approach. Keywords: Brain flattening, functional MRI, harmonic maps, segmentation. This paper has been accepted for publication in IEEE Transactions on Medical Imaging. 1 Introduction Recently a number of techniques have been proposed to obtain a flattened representation of the cortical surface; see, e.g., [4, 5, 6, 14, 24] and the references therein. Flattening the brain surface has uses in many areas including functional magnetic resonance imaging. Indeed, since it is important to visualize functional magnetic resonance imaging data for neural activity within the three dimensional folds of the brain, ...

Abstract—Lazy Sweep Ray Casting is a fast algorithm for rendering general irregular grids. It is based on the sweep-plane paradigm, and it is able to accelerate ray casting for rendering irregular grids, including disconnected and nonconvex (even with holes) unstructured irregular grids with a rendering cost that decreases as the “disconnectedness ” decreases. The algorithm is carefully tailored to exploit spatial coherence even if the image resolution differs substantially from the object space resolution. Lazy Sweep Ray Casting has several desirable properties, including its generality, (depth-sorting) accuracy, low memory consumption, speed, simplicity of implementation, and portability (e.g., no hardware dependencies). We establish the practicality of our method through experimental results based on our implementation, which is shown to be substantially faster (by up to two orders of magnitude) than other algorithms implemented in software. We also provide theoretical results, both lower and upper bounds, on the complexity of ray casting of irregular grids.

In this paper we present a novel framework for direct volume rendering using a splatting approach based on elliptical Gaussian kernels. To avoid aliasing artifacts, we introduce the concept of a resampling filter combining a reconstruction with a low-pass kernel. Because of the similarity to Heckbert’s EWA (elliptical weighted average) filter for texture mapping we call our technique EWA volume splatting. It provides high image quality without aliasing artifacts or excessive blurring even with non-spherical kernels. Hence it is suitable for regular, rectilinear, and irregular volume data sets. Moreover, our framework introduces a novel approach to compute the footprint function. It facilitates efficient perspective projection of arbitrary elliptical kernels at very little additional cost. Finally, we show that EWA volume reconstruction kernels can be reduced to surface reconstruction kernels. This makes our splat primitive universal in reconstructing surface and volume data.

In this paper, we consider a novel 3D visualization technique based on surface flattening for virtual colonoscopy. Such visualization methods could be important in virtual colonoscopy since they have the potential for non-invasively determining the presence of polyps and other pathologies. Further, we demonstrate a method which presents a surface scan of the entire colon as a cine, and affords viewer the opportunity to examine each point on the surface without distortion. We use certain angle-preserving mappings from differential geometry in order to derive an explicit method for flattening surfaces obtained from 3D colon CT imagery. Indeed, we describe a general method based on a discretization of the Laplace-Beltrami operator for flattening a surface onto the plane in a manner which preserves the local geometry. From a triangulated surface representation of the colon, we indicate how the procedure may be implemented using a finite element technique, which takes into acc...

Abstract — While there have been advances in visualization systems, particularly in multi-view visualizations and visual exploration, the process of building visualizations remains a major bottleneck in data exploration. We show that provenance metadata collected during the creation of pipelines can be reused to suggest similar content in related visualizations and guide semi-automated changes. We introduce the idea of query-by-example in the context of an ensemble of visualizations, and the use of analogies as first-class operations in a system to guide scalable interactions. We describe an implementation of these techniques in VisTrails, a publicly-available, open-source system. Index Terms—visualization systems, query-by-example, analogy 1

Introduction Physical phenomena often vary substantially in scale. There can be large regions where a given physical quantity only varies slightly. At the same time, there can be small regions where the same quantity changes rapidly. Adaptive mesh refinement (AMR) ,see [1, 2, 3], is a technique used in computational fluid dynamics (CFD) to simulate phenomena characterized by drastically varying scales. By using a set of nested grids at different resolutions, AMR combines the topological simplicity of structured rectilinear grids permitting the efficient computation and storage of the result with the adaptivity to changes in spatial resolution of unstructured grids. The data sets we visualize result from the simulation of astrophysical phenomena by Bryan et al. [3] using the Berger and Colella [1] AMR algorithm. They consist of a hierarchy of grids of increasing resolutions. Each level consists of a number of axisaligned rectilinear grids with data samples associated with the cell cen

This paper describes vlib, a generic application programming interface for volume graphics which supports many of the significant developments in the field to date. We present an overview of the interface and describe how its novel object modeling framework is able to facilitate a variety of modeling and rendering effects, including a method of achieving spatial deformation. We also discuss a volumetric ray-tracing algorithm for producing high quality images with a minimal memory overhead. The paper closes with some comments on our freeware implementation of the interface.