Geometric anticipation: assisting users in 2D layout tasks

We describe an experimental interface that anticipates a user's intentions and accommodates predicted changes in advance. Our canonical example is an interactive version of ``magnetic poetry'' in which rectangular blocks containing single words can be juxtaposed to form arbitrary sentences or ``poetry.'' The user can rearrange the blocks at will, forming and dissociating word sequences. A crucial attribute of the blocks in our system is that they anticipate insertions and gracefully rearrange themselves in time to make space for a new word or phrase. The challenges in creating such an interface are three fold: 1) the user's intentions must be inferred from noisy input, 2) arrangements must be altered smoothly and intuitively in response to anticipated changes, and 3) new and changing goals must be handled gracefully at any time, even in mid animation. We describe a general approach for handling the dynamic creation and deletion of organizational goals. Fluid motion is achieved by continually applying and correcting goal-directed forces to the objects. Future applications of this idea include the manipulation of text and graphical elements within documents and the manipulation of symbolic information such as equations

Geometric anticipation: assisting users in 2D layout tasks

We describe an experimental interface that anticipates a user's intentions and accommodates predicted changes in advance. Our canonical example is an interactive version of ``magnetic poetry'' in which rectangular blocks containing single words can be juxtaposed to form arbitrary sentences or ``poetry.'' The user can rearrange the blocks at will, forming and dissociating word sequences. A crucial attribute of the blocks in our system is that they anticipate insertions and gracefully rearrange themselves in time to make space for a new word or phrase. The challenges in creating such an interface are three fold: 1) the user's intentions must be inferred from noisy input, 2) arrangements must be altered smoothly and intuitively in response to anticipated changes, and 3) new and changing goals must be handled gracefully at any time, even in mid animation. We describe a general approach for handling the dynamic creation and deletion of organizational goals. Fluid motion is achieved by continually applying and correcting goal-directed forces to the objects. Future applications of this idea include the manipulation of text and graphical elements within documents and the manipulation of symbolic information such as equations

Towards Accurate And Efficient Volume Rendering

This thesis is concerned with improvements to algorithms for volume rendering; a technique that provides scientists with the means for visual exploration of three-dimensional data. Despite its numerous successes, and its increasing use within the scientific community, state-of-the-art volume rendering algorithms have many shortcomings. Difficulties include: ensuring the accuracy of the rendered images, producing images with modest computational resources, and rendering the diverse types of data that are currently being produced. The work in this thesis was motivated by the demands of an ongoing visualization project in four-dimensional cardiac visualization. We present solutions to some key problems in ensuring accuracy and in producing algorithms that can scale to handle large datasets. Although the theoretical work in this thesis applies to arbitrary data topologies, our implementations have assumed that the data is defined by sample points on a regular rectilinear grid. In the area of accuracy, we focus on the error that is introduced during volume projection. This phase of the volume rendering process involves the evaluation of the emission-absorption volume rendering line integral. This thesis presents four techniques for controlled precision volume integration. These schema depart from existing approaches in that they provide error bounds along with the solutions they generate. In each case, the error analysis leads to an algorithm for evaluating the integral to any specified tolerance. Our investigations into efficiency issues have resulted in two advances. First, an adaptive error bracketing scheme is presented that builds on the controlled precision volume integration methods. Using adaptive error bracketing, the solution for a viewing ray is continually refined until a user-specified error tolerance is met. The algorithm allows processing of the data without imposing a strict front-to-back or back-to-front evaluation order. Second, a suite of tools are presented that can be used to efficiently compute perspective projections of volume data. These include a paging strategy that is useful when a dataset is too large to fit into RAM memory and a ray splitting technique for adaptive supersampling. The latter technique ensures that all data features contribute to the final image while avoiding overcomputation in regions close to the eyepoint

Controlled Precision Volume Integration

Traditional methods for evaluating the low-albedo volume rendering integral do not include bounds on the magnitude of approximation error. In this paper, we examine three techniques for solving this integral with error bounds: trapezoid rule, Simpson's rule, and a power series method. In each case, the expression for the error bound provides a mechanism for computing the integral to any specified precision. The formulations presented are appropriate for polynomial reconstruction from point samples; however, the approach is considerably more general. The three techniques we present differ in relative efficiency for computing results to a given precision. The trapezoid rule and Simpson's rule are most efficient for low- to medium-precision solutions. The power series method converges rapidly to a machine precision solution, providing both an efficient means for high-accuracy volume rendering, and a reference standard by which other approximations may be measured. CR Categoriesand Subject..