Information Visualization

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Information Visualization
Focus Context
Fengdong Du
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Based on the paper
A Review and Taxonomy of Distortion-Oriented
Presentation Techniques by Y.K Leung and M.D
Apperley
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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?

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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

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• 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.

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Distortion-based Techniques

• Bifocal Display
• Polyfocal Display
• Perspective Wall
• Fisheye View
• Graphical Fisheye View

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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.

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• 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.

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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.

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Bifocal Display

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

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Fold
Project
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Demagnified in X and Y, but no distortion
Demagnified and distorted in X
No demagnification and distortion
Demagnified and distorted in Y
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• Has the disadvantage of discontinuity of
  magnification at the boundary.

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Polyfocal Display

• Proposed by Kadmon and Shlomi1978 for
  presentation of statistical data on cartographic
  maps.
• Mathematical foundation for many distortion-based
  techniques.
• Highest peak is the focus of the display

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• 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.

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Multifocal Polyfocal Projection
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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.

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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.

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Increasing demagnification rate
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The view is dependent on the length of the wall,
the width of the view port, the angle T, the size
of the central region.
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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.

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• 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.

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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

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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.

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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.

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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.

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Stretchable Rubber Sheet
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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.

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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.