Kellogg S. Booth

Testing for the consecutive ones property, interval graphs, and graph planarity using PQ-tree algorithms

A data structure called a PQ-tree is introduced. PQ-trees can be used to represent the permutations of a set U in which various subsets of U occur consecutively. Efficient algorithms are presented for manipulating PQ-trees. Algorithms using PQ-trees are then given which test for the consecutive ones property in matrices and for graph planarity. The consecutive ones test is extended to a test for interval graphs using a recently discovered fast recognition algorithm for chordal graphs. All of these algorithms require a number of steps linear in the size of their input.

Hipikat: a project memory for software development

Sociological and technical difficulties, such as a lack of informal encounters, can make it difficult for new members of noncollocated software development teams to learn from their more experienced colleagues. To address this situation, we have developed a tool, named Hipikat that provides developers with efficient and effective access to the group memory for a software development project that is implicitly formed by all of the artifacts produced during the development. This project memory is built automatically with little or no change to existing work practices. After describing the Hipikat tool, we present two studies investigating Hipikats usefulness in software modification tasks. One study evaluated the usefulness of Hipikats recommendations on a sample of 20 modification tasks performed on the Eclipse Java IDE during the development of release 2.1 of the Eclipse software. We describe the study, present quantitative measures of Hipikats performance, and describe in detail three cases that illustrate a range of issues that we have identified in the results. In the other study, we evaluated whether software developers who are new to a project can benefit from the artifacts that Hipikat recommends from the project memory. We describe the study, present qualitative observations, and suggest implications of using project memory as a learning aid for project newcomers.

Heuristics for ray tracing using space subdivision

Ray tracing requires testing of many rays to determine intersections with objects. A way of reducing the computation is to organize objects into hierarchical data structures. We examine two heuristics for space subdivisions using bintrees, one based on the intuition that surface area is a good estimate of intersection probability, one based on the fact that the optimal splitting plane lies between the spatial median and the object median planes of a volume. Traversal algorithms using cross links between nodes are presented as generalizations of ropes in octrees. Simulations of the surface area heuristic and the cross link scheme are presented. These results generalize to other hierarchical data structures.

Fish tank virtual reality

The defining characteristics of what we call “Fish Tank Virtual Reality” are a stereo image of a three dimensional (3D) scene viewed on a monitor using a perspective projection coupled to the head position of the observer. We discuss some of the relative merits of this mode of viewing as compared to head mounted stereo displays. In addition, we report the experimental investigation of the following variables: 1) whether or not the perspective view is coupled to the actual viewpoint of the observer, 2) whether stereopsis is employed. Experiment 1 involved the subjective comparison of pairs of viewing conditions and the results suggest that head coupling may be more important than stereo in yielding a strong impression of three dimensionality. Experiment 2 involved subjects tracing a path from a leaf of a 3D tree to the correct root (there were two trees intermeshed). The error rates ranged from 22% in the pictorial display, to 1.3% in the head coupled stereo display. The error rates for stereo alone and head coupling alone were 14.7% and 3.2% respectively. We conclude that head coupling is probably more important than stereo in 3D visualization and that head coupling and stereo combined provide an important enhancement to monitor based computer graphics.

Evaluating 3D task performance for fish tank virtual worlds

“Fish tank virtual reality” refers to the use of a standard graphics workstation to achieve real-time display of 3D scenes using stereopsis and dynamic head-coupled perspective. Fish tank VR has a number of advantages over head-mounted immersion VR which makes it more practical for many applications. After discussing the characteristics of fish tank VR, we describe a set of three experiments conducted to study the benefits of fish tank VR over a traditional workstation graphics display. These experiments tested user performance under two conditions: (a) whether or not stereoscopic display was used and (b) whether or not the perspective display was coupled dynamically to the positions of a user’s eyes. Subjects using a comparison protocol consistently preferred head coupling without stereo over stereo without head coupling. Error rates in a tree-tracing task similar to one used by Sollenberger and Milgram showed an order of magnitude improvement for head-coupled stereo over a static (nonhead-coupled) display, and the benefits gained by head coupling were more significant than those gained from stereo alone. The final experiment examined two factors that are often associated with human performance in virtual worlds: the lag (or latency) in receiving and processing tracker data arid the rate at which frames are updated. For the tree-tracing task, lag had a larger impact on performance than did frame update rate, with lag having a multiplicative effect on response time. We discuss the relevance of these results for the display of complex 3D data and highlight areas requiring further study,

High-speed visual estimation using preattentive processing

A new method is presented for performing rapid and accurate numerical estimation. The method is derived from an area of human cognitive psychology called preattentive processing. Preattentive processing refers to an initial organization of the visual field based on cognitive operations believed to be rapid, automatic, and spatially parallel. Examples of visual features that can be detected in this way include hue, intensity, orientation, size, and motion. We beleive that studies from preattentive vision should be used to assist in the design of visualization tools, especially those for which high-speed target detection, boundary identification, and region detection are important. In our present study, we investigated two known preattentive features (hue and orientation) in the context of a new task (numerical estimation) in order to see whether preattentive estimation was possible. Our experiments tested displays that were designed to visualize data from salmon migration simulations. The results showed that rapid and accurate estimation was indeed possible using either hue or orientation. Furthermore, random variation in one of these features resulted in no interference when subjects estimated the percentage of the other. To test the generality of our results, we varied two important display parameters—display duration and feature difference—and found boundary conditions for each. Implications of our results for application to real-world data and tasks are discussed.

GeneyTM: designing a collaborative activity for the palmTM handheld computer

This paper describes a project to explore issues surrouding the development of a collaborative handheld educational application for children. A user-centered, iterative design process was used to develop GeneyTM, a collaborative problem solving application to help children explore genetic concepts using PalmTM handheld computers. The design methodology utilized mock-ups of representative tasks and scenarios, pre-design meetings with targets users, prototype development, and feedback sessions with target users. The results of this work identify an effective way of utilizing handheld computers for collaborative learning and provide important insights into the design of handheld applications for children. This work also illustrates the necessity of user-centered design when new user groups are targeted, especially when novel user interface paradigms are employed that go beyond current windows-based interfaces.

A Linear Time Algorithm for Deciding Interval Graph Isomorphism

Author(s): Lueker, George S.; Booth, Kellogg S. | Abstract: A graph is an interval graph if and only if each of its vertices can be associated with an interval on the real line in such a way that two vertices are adjacent in the graph exactly when the corresponding intervals have a nonempty intersection. An efficient algorithm for testing isomorphism of interval graphs is implemented using a data structure called a PQ-tree. The algorithm runs in 0(n + e) steps for graphs having n vertices and e edges. It is shown that for a somewhat larger class of graphs, namely the chordal graphs, isomorphism is as hard as for general graphs.

Playing together beats playing apart, especially for girls

This paper describes follow-on studies focusing on how gender and grouping affects performance and attitudes of children playing a puzzle solving game called The Incredible Machine (TIM). We found that children playing together on one machine solved significantly more puzzles than children playing alone on one machine. Female/Female pairs playing together on one machine, on average, completed significantly more puzzles than Female/Female pairs playing side-by-side on two computers. In addition, the level of motivation to continue playing the game was affected by the opportunity to play with a partner, and success in the game. This paper describes follow-on studies focusing on how gender and grouping affects performance and attitudes of children playing a puzzle solving game called The Incredible Machine (TIM). We found that children playing together on one machine solved significantly more puzzles than children playing alone on one machine. Female/Female pairs playing together on one machine, on average, completed significantly more puzzles than Female/Female pairs playing side-by-side on two computers. In addition, the level of motivation to continue playing the game was affected by the opportunity to play with a partner, and success in the game

Shadow reaching: a new perspective on interaction for large displays

We introduce Shadow Reaching, an interaction technique that makes use of a perspective projection applied to a shadow representation of a user. The technique was designed to facilitate manipulation over large distances and enhance understanding in collaborative settings. We describe three prototype implementations that illustrate the technique, examining the advantages of using shadows as an interaction metaphor to support single users and groups of collaborating users. Using these prototypes as a design probe, we discuss how the three components of the technique (sensing, modeling, and rendering) can be accomplished with real (physical) or computed (virtual) shadows, and the benefits and drawbacks of each approach.