Victoria Interrante

A novel cubic-order algorithm for approximating principal direction vectors

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.

User Studies: Why, How, and When?

User studies offer a scientifically sound method to measure a visualizations performance. Reasons abound for pursuing user studies, particularly when evaluating the strengths and weaknesses of different visualization techniques. A good starting point in any study is the scientific or visual design question to be examined. This drives the process of experimental design. A poorly designed experiment will yield results of only limited value. Although a comprehensive discussion of experimental design is beyond the scope of the article, we offer suggestions and lessons learned. We also describe how we designed experiments to answer important questions from our own research.

Enhancing transparent skin surfaces with ridge and valley lines

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. The 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. We describe a promising technique for communicating the shape and position of the transparent skin surface while at the same time minimally occluding underlying isointensity dose surfaces and anatomical objects: adding a sparse, opaque texture comprised of a small set of carefully chosen lines. We explain the perceptual motivation for explicitly drawing ridge and valley curves on a transparent surface, describe straightforward mathematical techniques for detecting and rendering these lines, and propose a small number of reasonably effective methods for selectively emphasizing the most perceptually relevant lines in the display.

Distance perception in NPR immersive virtual environments, revisited

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.

Line direction matters: an argument for the use of principal directions in 3D line drawings

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.

Visualizing 3D flow

Line integral convolution (LIC) is an elegant and versatile technique for representing directional information via patterns of correlation in a texture. In this article we discuss some of the facto...We discuss volume line integral convolution (LIC) techniques for effectively visualizing 3D flow, including using visibility-impeding halos and efficient asymmetric filter kernels. Specifically, we suggest techniques for selectively emphasizing critical regions of interest in a flow; facilitating the accurate perception of the 3D depth and orientation of overlapping streamlines; efficiently incorporating an indication of orientation into a flow representation; and conveying additional information about related scalar quantities such as temperature or vorticity over a flow via subtle, continuous line width and color variations.

Elucidating factors that can facilitate veridical spatial perception in immersive virtual environments

Ensuring veridical spatial perception in immersive virtual environments (IVEs) is an important yet elusive goal. In this paper, we present the results of two experiments that seek further insight into this problem. In the first of these experiments, initially reported in Interrante, Ries, Lindquist, and Anderson (2007), we seek to disambiguate two alternative hypotheses that could explain our recent finding (Interrante, Anderson, and Ries, 2006a) that participants appear not to significantly underestimate egocentric distances in HMD-based IVEs, relative to in the real world, in the special case that they unambiguously know, through first-hand observation, that the presented virtual environment is a high-fidelity 3D model of their concurrently occupied real environment. Specifically, we seek to determine whether people are able to make similarly veridical judgments of egocentric distances in these matched real and virtual environments because (1) they are able to use metric information gleaned from their exposure to the real environment to calibrate their judgments of sizes and distances in the matched virtual environment, or because (2) their prior exposure to the real environment enabled them to achieve a heightened sense of presence in the matched virtual environment, which leads them to act on the visual stimulus provided through the HMD as if they were interpreting it as a computer-mediated view of an actual real environment, rather than just as a computer-generated picture, with all of the uncertainties that that would imply. In our second experiment, we seek to investigate the extent to which augmenting a virtual environment model with faithfully-modeled replicas of familiar objects might enhance peoples ability to make accurate judgments of egocentric distances in that environment.

Volume rendering in radiation treatment planning

Successful treatment planning in radiation therapy depends in part on understanding the spatial relationship between patient anatomy and the distribution of radiation dose. Several visualizations based on volume rendering that offer potential solutions to this problem are presented. The visualizations use 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, metallic shading, surface and solid texturing, synthetic fog, shadows, and other artistic devices are used. Also outlined is a method based on 3-D mip maps for efficiently generating perspective volume renderings and beams-eye views.<<ETX>>

Effectively visualizing multi-valued flow data using color and texture

In this paper we offer several new insights and techniques for effectively using color and texture to simultaneously convey information about multiple 2D scalar and vector distributions, in a way that facilitates allowing each distribution to be understood both individually and in the context of one or more of the other distributions. Specifically, we introduce the concepts of: color weaving for simultaneously representing information about multiple co-located color encoded distributions; and texture stitching for achieving more spatially accurate multi-frequency line integral convolution representations of combined scalar and vector distributions. The target application for our research is the definition, detection and visualization of regions of interest in a turbulent boundary layer flow at moderate Reynolds number. In this work, we examine and analyze streamwise-spanwise planes of three-component velocity vectors with the goal of identifying and characterizing spatially organized packets of hairpin vortices.

Transitional environments enhance distance perception in immersive virtual reality systems

Several experiments have provided evidence that ego-centric distances are perceived as compressed in immersive virtual environments relative to the real world. The principal factors responsible for this phenomenon have remained largely unknown. However, recent experiments suggest that when the virtual environment (VE) is an exact replica of a users real physical surroundings, the persons distance perception improves. Furthermore, it has been shown that when users start their virtual reality (VR) experience in such a virtual replica and then gradually transition to a different VE, their sense of presence in the actual virtual world increases significantly. In this case the virtual replica serves as a transitional environment between the real and virtual world. In this paper we examine whether a persons distance estimation skills can be transferred from a transitional environment to a different VE. We have conducted blind walking experiments to analyze if starting the VR experience in a transitional environment can improve a persons ability to estimate distances in an immersive VR system. We found that users significantly improve their distance estimation skills when they enter the virtual world via a transitional environment.