Interactive Information Visualization of a Million Items

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Interactive Information Visualization of a
Million Items

• Jean-Daniel Fekete Catherine Plaisant
• Human Computer Interaction Laboratory
• University of Maryland
• http//www.cs.umd.edu/hcil
• Originally Presented at InfoVis 2002

Reviewed for CS 526 by John T. Bell
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Project Goals

• To display very large numbers of data items
• Each item to be displayed as a separate atomic
  object, not aggregated.
• Visualization to be cognitively perceptual.
• Provide continuous interaction and smooth
  animation when changing viewing parameters or
  view types.

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Classic Visualization Techniques

• Overlapping Space-Filling(
  Scatter Plot ) ( Treemap )

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TreeMap of a Million Items
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TreeMap of a UNIX Filesystem
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Human PerceptionPre-Attentive Graphical Features

• Nelson
• Johnson
• Yu
• Buy
• Bush
• Bell
• Theys, M.
• Theys, C.

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Pre-Attentive Features ( Healy 11 )

• binocular luster
• stereo depth
• 3D depth cues
• lighting direction

• orientation
• length
• width
• size
• curvature
• number
• terminators

• intersection
• closure
• color (hue)
• intensity
• flicker
• direction of motion

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Interactive Techniques ( Ahlberg 1 )

• Overview, zoom in, filter, details
• Display query results
• Rapid, incremental, reversible control
• Selection by pointing, not typing
• Immediate continuous feedback
• Techniques for large data sets include space
  time multiplexing space deformations (
  aggregation, sampling, LOD )

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Technical Constraints

• 1600 x 1200 displays - 1.92 Million pixels
• Refresh rate of 10 fps requires special
  techniques. ( Graphics cards at 15M tps,
  achievable in practice only with ? strips. )
• This work done with NVidia GeForce3 cards, 2GHz
  computers, OpenGL
• Interactive speeds achieved by cleverly
  offloading rendering tasks to the GPU

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Individual Item Display

• Items displayed as shaded quads, w/o borders
• Information attributes include size, position,
  color ( categorical or value based ), and
  intensity ( value based )
• Color indicated using one-dimensional texture
  indexes. ( One byte per vertex, not 3 or 4 )
• Data per vertex X, Y, Z, and S ( text. Index )

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Illustration of Shaded Rectangles
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Synthetic Overlap

• Stencil Buffer can be accessed to determine
  overlap counts and/or filtering accordingly

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Transparency Stereo Vision

• Transparency can be useful in overlap situations,
  BUT it interferes with pre-attentive processing
  by blending colors.
• Therefore only useful when dynamically adjustable
  for exploring overlap information.
• Stereo vision also of limited usefulness with
  overlap exploration, for the same reasons.

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Animation and Interaction

• Data exploration often involves changing views -
  This can cause problems correlating information
  in different views.
• Flipping can be used when geometry is fixed.
• Linear interpolation works when layout fixed.
• Otherwise interpolate in two stages Postion
  first, then size. ( Treemaps can be squarified or
  slice-and-dice. )
• Texture maps can speed up the process, by warping
  a square area as a whole unit.

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Animation of Property Changes
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Animating View Changes
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Implementing Dynamic Queries

• Used to dynamically filter the data based on a
  range of values for a particular attribute.
• Items are stored as display lists on the GPU
• Z-coordinate is mapped to changing attribute
• Near and far clipping planes are adjusted based
  on slider values, and the GPU solves the problem
  of which items to display.
• For PCs with limited video RAM, use OpenGL points
  of varying sizes instead of quads ( NVidia Vertex
  programs extension. )

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Performance

• 23,000 lines of C, reads XML or directory
• NVidia GeForce 3 on 2GHz Pentium and 3Dlab
  Wildcat 5110 on dual 1.7 GHz Pentium
• Sustainable performance 2.5 M Quads / sec
• 10 fps treemap animations for any treemap,
  through the use of texture maps.
• 3 / 6 fps scatterplots, for animations / queries.

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Conclusions Future Work

• 1M items have been displayed on 1600x1200,
  interactively without aggregation.
• New techniques have been developed to take
  advantage of modern GPU capabilities.
• Future data explorations include U MD catalog and
  circulation data and U.S. Census data, involving
  domain experts in user testing.

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Web Site, Downloads, Movies

• Http//www.cs.umd.edu/hcil/millionvis

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References - General

• Jean-Daniel Fekete Catherine Plaisant,
  Interacive Information Visualization of a
  Million Items, InfoVis 2002.
• 1 Ahlberg et al., Visual Information Seeking
  Tight Coupling of Dynamic Query Filters with
  Starfield Display, Human Factors in Computing
  Systems, 1994.
• 11 Healy et al., Visualizing Real-Time
  Multivariate Data using Preattentive Processing,
  ACM Transactions on Modeling and Computer
  Simulation, 1995.

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References - Treemaps

• 4 Bederson et al., Ordered and Quantum
  Treemaps Making Effective Use of 2D Space to
  Display Hierarchies, ACM Transactions on
  Computer Graphics.
• 13 Johnson et al., Tree-maps A Space-Filling
  Approach to the Visualization of Hierarchical
  Information Structures, IEEE Visualization 91.