Computer Science and Engineering

Abstract Marsupial robotics is a field which requires a high initial investment prior to experiments. We present a new simulation tool used for marsupial actions, enabling research in the area of marsupial robotics. A flexible abstraction for a marsupial system is presented which allows for the modeling of many differing marsupial models. The interface and simulation model are covered in detail. Two experiments are presented which use the model to demonstrate the flexibility and range of the abstraction and simulation.

Abstract The performance of systems for human activity recognition depends heavily on the placement of cameras observing the scene. This work addresses the question of the optimal placement of cameras to maximize the performance of these types of recognition tasks. Specifically, our goal is to optimize the quality of the joint observability of the tasks being performed by the subjects in an area.

There are a number of applications in computer graphics that require as a first step the accurate estimation of principal direction vectors at arbitrary vertices on a triangulated surface. Although several methods for calculating principal directions over such models have been previously proposed, we have found in practice that all exhibit unexplained large errors in some cases. In this article, we describe our theoretical and experimental investigations into possible sources of errors in the approximation of principal direction vectors from triangular meshes, and suggest a new method for estimating principal directions that can yield better results under some circumstances.

This paper discusses strategies for effectively portraying 3D flow using volume line integral convolution. Issues include defining an appropriate input texture, clarifying the distinct identities and relative depths of the advected texture elements, and selectively highlighting regions of interest in both the input and output volumes. Apart from offering insights into the greater potential of 3D LIC as a method for effectively representing flow in a volume, a principal contribution of this work is the suggestion of a technique for generating and rendering 3D visibility-impeding "halos" that can help to intuitively indicate the presence of depth discontinuities between contiguous elements in a projection and thereby clarify the 3D spatial organization of elements in the flow. The proposed techniques are applied to the visualization of a hot, supersonic, laminar jet exiting into a colder, subsonic coflow.

While many factors contribute to shape perception, psychological research indicates that the direction of lines on the surface may have an important influence. This is especially the case when other techniques (shading, silhouetting) do not present sufficient shape information. The psychology literature suggests that lines in the principal directions of curvature may communicate surface shape better than lines in other directions. Moreover, principal directions have the quality of geometric invariance so line directions are based on the surface geometry and are viewpoint and light source independent, and the lines do not move above over the surface during animation unless desired. In this work we describe principal direction line drawings which show the flow of curvature over the surface. The technique is presented for arbitrary surfaces represented by either 3D volume data or a polygonal surface mesh. The latter format is common in the field of computer graphics yet thus far has not been widely used for principal direction estimation. The methods offered in this paper can be used alone or in conjunction with other NPR techniques to improve artistic 3D renderings of arbitrary surfaces.

There are many applications that can benefit from the simultaneous display of multiple layers of data. The objective in these cases is to render the layered surfaces in a such way that the outer structures can be seen and seen through at the same time. This paper focuses on the particular application of radiation therapy treatment planning, in which physicians need to understand the three-dimensional distribution of radiation dose in the context of patient anatomy.

A n elegant and versatile technique, line integral convolution (LIC) 1,2 represents directional information via patterns of correlation in a texture. Although most commonly used to depict 2D flow, or flow over a surface in 3D, LIC methods can also portray 3D flow through a volume. 1,3 However, the popularity of LIC as a device for illustrating 3D flow has historically been limited by the computational expense of generating and rendering such a 3D texture and by the difficulties inherent in clearly and effectively conveying the directional information embodied in the resulting volumetric output textures.

Considerable evidence suggests that a viewer's perception of the 3D shape of a polygonally-defined object can be significantly affected (either masked or enhanced) by the presence of a surface texture pattern. However, investigations into the specific mechanisms of texture's effect on shape perception are still ongoing and the question of how to design and apply a texture pattern to a surface in order to best facilitate shape perception remains open. Recently, we have suggested that, for anisotropic texture patterns, the accuracy of shape judgments may be significantly affected by the orientation of the surface texture pattern anisotropy with respect to the principal directions of curvature over the surface. However, it has been difficult, until this time, to conduct controlled studies specifically investigating the effect of texture orientation on shape perception because there has been no simple and reliable method for texturing an arbitrary doubly curved surface with a specified input pattern such that the dominant orientation of the pattern everywhere follows a predefined directional vector field over the surface, while seams and projective distortion of the pattern are avoided. In this paper, we present a straightforward and highly efficient method for achieving such a texture and describe how it can potentially be used to enhance shape representation. Specifically, we describe a novel, efficient, automatic algorithm for seamlessly synthesizing, from a sample 2D pattern, a high resolution fitted surface texture in which the dominant orientation of the pattern locally follows a specified vector field over the surface at a per-pixel level and in which seams, projective distortion, and repetition artifacts in the texture pattern are nearly completely avoided. We demonstrate the robustness of our method with a variety of texture swatches applied to standard graphics data sets and we explain how our method can be used to facilitate research in the perception of shape from texture.

Numerous previous studies have suggested that distances appear to be compressed in immersive virtual environments presented via head mounted display systems, relative to in the real world. However, the principal factors that are responsible for this phenomenon have remained largely unidentified. In this paper we shed some new light on this intriguing problem by reporting the results of two recent experiments in which we assess egocentric distance perception in a high fidelity, low latency, immersive virtual environment that represents an exact virtual replica of the participant's concurrently occupied real environment. Under these novel conditions, we make the startling discovery that distance perception appears not to be significantly compressed in the immersive virtual environment, relative to in the real world.

Successful treatment planning in radiation therapy depends in part on understanding the spatial relationship between patient anatomy and the distribution of radiation dose. We present several visualizations based on volume rendering that offer potential solutions to this problem. The visualizations employ region boundary surfaces to display anatomy, polygonal meshes to display treatment beams, and isovalue contour surfaces to display dose. To improve perception of spatial relationships, we use metallic shading, surface and solid texturing, synthetic fog, shadows, and other artistic devices. Also outlined is a method based on 3D mip maps for efficiently generating perspective volume renderings and beam's-eye views. To evaluate the efficacy of these visualizations, we are building a radiotherapy planning system based on a Cray YMP and the Pixel-Planes 5 raster display engine. The system will allow interactive manipulation of beam geometry, dosimetry, shading, and viewing parameters, and will generate volume renderings of anatomy and dose in real time.

Transparency can be a useful device for simultaneously depicting multiple superimposed layers of information in a single image. However, in computer-generated picturesas in photographs and in directly viewed actual objects -it can often be difficult to adequately perceive the threedimensional shape of a layered transparent surface or its relative depth distance from underlying structures.

When an immersive virtual environment represents a space that is larger than the available space within which a user can travel by directly walking, it becomes necessary to consider alternative methods for traveling through that space. The traditional solution is to require the user to travel 'indirectly', using a device that changes his viewpoint in the environment without actually requiring him to move -for example, a joystick. However, other solutions involving variations on direct walking are also possible. In this paper, we present a new metaphor for natural, augmented direct locomotion through moderately large-scale immersive virtual environments (IVEs) presented via head mounted display systems, which we call seven league boots. The key characteristic of this method is that it involves determining a user's intended direction of travel and then augmenting only the component of his or her motion that is aligned with that direction.

I n our ongoing quest to convey more information more clearly in a single image, harnessing the full potential of texture for data representation remains an elusive goal. Others have begun excellent work in this area, 1-3 and my efforts are inspired by their example. The grail that I seek is a partially ordered multidimensional palette of richly detailed and varying texture patterns that can be used-in conjunction with lightness and hue-to represent multivariate information. The goal is to facilitate the flexible visual appreciation of the correlations of various quantities across the different dimensions. The approach that I outline here departs a bit from the norm, but is motivated by a desire to proceed more directly from my vision of what I want to achieve, unrestrained by the limitations of the tools I have on hand. In the following discussion, I motivate the adoption of rich, natural textures-resembling those from photographic images 4 -as elemental primitives and sketch some of the approaches that we can take to enhance our understanding of how to effectively harness their properties. My intent here is not to present results, but to expound on the issues and conclude with the questions to which we're still seeking answers.

This paper discusses techniques for extracting feature lines from three-dimensional unstructured grids. Our twin objectives are to facilitate the interactive manipulation of these typically very large and dense meshes, and to clarify the visualization of the solution data that accompanies them.

As visualization researchers, we are interested in gaining a better understanding of how to effectively use texture to facilitate shape perception. If we could design the ideal texture pattern to apply to an arbitrary smoothly curving surface in order to enable its 3D shape to be most accurately and effectively perceived, what would the characteristics of that texture pattern be? In this paper we describe the results of a comprehensive controlled observer experiment intended to yield insight into that question.

Studies have shown that observers' judgments of surface orientation and curvature are affected by the presence of surface texture pattern. However, the question of designing a texture pattern that does not hide the surface information nor conveys a misrepresentation of the surface remains unsolved. The answer to this question has important potential impact across a wide range of visualization applications. Molecular modeling and radiation therapy are among the many fields that are in need of accurately visualizing their data that could benefit from such methods.