Information Visualization

1. Information Visualization Focus + Context Fengdong Du

2. Based on the paper: “A Review and Taxonomy of Distortion-Oriented Presentation Techniques” by Y.K Leung and M.D Apperley

3. Introduction • Large amount of information vs. relatively small computer screen. • locating a given item of information • interpreting an item of information? • relating an item with some other items?

4. Two Category of Approaches • Non-distortion-oriented approaches. • Displaying a portion of the information at a time; • Scrolling or paging access • Providing hierarchical access • Structure-specific presentation • Weakness

5. (Continued) • Distortion-oriented Approaches: • Distort an image of large amount of information so that it can fit in screen. • Allow the user to examine a local area in detail; • At the same time, present a global view of the information space; • Provide navigation mechanism.

7. Distortion-based Techniques • Bifocal Display • Polyfocal Display • Perspective Wall • Fisheye View • Graphical Fisheye View

8. Idea of Distortion-based Techniques • Co-existence of local details with global context at reduced magnification. • A focus region to display detailed information. • Demagnified view of the peripheral areas is presented around the focus area.

10. (Continued) • A distorted view is created by applying a transformation function to an undistorted image. • A magnification function, provides a profile of the magnification factors for the entire area of image.

12. System Response Issue • Depends on three factors: • Complexity of the transformation function. • Amount of information and details to be presented. • Computational power of the hardware.

13. Bifocal Display • Distortion at one or two dimensions with linear transformation function. • Combination of detailed view and two distorted side views.

14. (Continued) Fold Project

16. (Continued)

17. (Continued) • Has the disadvantage of discontinuity of magnification at the boundary.

18. Polyfocal Display • Proposed by Kadmon and Shlomi[1978] for presentation of statistical data on cartographic maps. • Mathematical foundation for many distortion-based techniques. • “Highest peak is the focus of the display”

20. (Continued) • The magnification function is controlled two sets of parameters: • Magnification at the peak • Rate of change of magnification with the distance from the peak • The boundary of the display is distorted as well.

21. Multifocal Polyfocal Projection

22. Multifocal Polyfocal Projection • Multiple peaks in the display • No restriction on the numbers of peaks in the magnification function. • Need to consider the computation time and the comprehensibility of the distorted image.

23. Perspective Wall • A conceptual descendent of the Bifocal display. • Smoothly integrated detailed and contextual views. • Side panels are demagnified directly proportional to their distance from the viewer.

25. Increasing demagnification rate

26. The view is dependent on the length of the wall, the width of the view port, the angle Θ, the size of the central region.

27. Fisheye View • Originally proposed by Furnas (1986), but many variations of applications. • Basic idea: more relevant information presented in great detail; the less relevant information presented as an abstraction. • Relevance is computed on basis of the importance of information elements and their distance to the focus.

28. (Continued) • Degree of interest (DOI) function: • DOI(a|.=b) = API(a) – D(A,b) • DOI(a|.=b): DOI of a, given the current focus is b. • API(a): static global apriori importance measure. • D(a,b): distance between a and b.

30. Graphical Fisheye View • An extension of the fisheye view concept. • Could be also considered as a special case of polyfocal display. • Topological network, multi-layer data and hierarchical structures

33. Taxonomy of Distortion-based Techniques • Magnification • Piecewise continuous magnification function • Bifocal display: constant magnifications • Perspective wall: varying magnifications • Continuous magnification function • Polyfocal display • Fisheye view • Continuous magnification function can be simulated by piecewise functions.

35. Continuous Magnification Function • Distortion of boundary problem: • Apply the transformation in X and Y directions independently. • Pull the boundary and remap the distorted image onto a rectangular size.

36. Unified Theory • Treat the displayed information as it was printed on a stretchable rubber sheet with rigid frame. • Any stretching in one part of the sheet results in an equivalent amount of shrinkage in other areas. • The consequence of the stretching and the shrinking of the sheet is an overall distorted view.

37. Stretchable Rubber Sheet

38. Implementation Issues • Distortion-based techniques have widely different complexities, depending on the transformation function. • Tradeoff needs to be made to choose computational power and the system memory. • Distortion with continuous magnification functions are hard to apply the cutting and pasting technique.

39. Conclusion • Distortion-based techniques can be categorized as: • Continuous magnification function • Non-continuous magnification function • The unified theory of all distortion-based techniques are “stretchable rubble sheet”. • The taxonomy helps us to understand the relationship between these techniques.