Interactive Information Visualization of a Million Items Jean-Daniel

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 Info. Vis 2002 Reviewed for CS 526 by John T. Bell

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.

Classic Visualization Techniques Overlapping ( Scatter Plot ) Space-Filling ( Treemap )

Tree. Map of a Million Items

Tree. Map of a UNIX Filesystem

Human Perception: Pre-Attentive Graphical Features Nelson Johnson Yu Buy Bush Bell Theys, M. Theys, C.

Pre-Attentive Features ( Healy [ 11 ] ) • • orientation length width size curvature number terminators • • • intersection closure color (hue) intensity flicker direction of motion • binocular luster • stereo depth • 3 D depth cues • lighting direction

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 )

Technical Constraints • 1600 x 1200 displays -> 1. 92 Million pixels • Refresh rate of 10 fps requires special techniques. ( Graphics cards at 15 M tps, achievable in practice only with Δ strips. ) • This work done with NVidia Ge. Force 3 cards, 2 GHz computers, Open. GL • Interactive speeds achieved by cleverly offloading rendering tasks to the GPU

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 )

Illustration of Shaded Rectangles

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

Transparency & Stereo Vision • Transparency can be useful in overlap situations, BUT it interferes with preattentive 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.

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.

Animation of Property Changes

Animating View Changes

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 Open. GL points of varying sizes instead of quads ( NVidia Vertex programs extension. )

Performance • 23, 000 lines of C++, reads XML or directory • NVidia Ge. Force 3 on 2 GHz Pentium and 3 Dlab 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.

Conclusions & Future Work • 1 M items have been displayed on 1600 x 1200, 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.

Web Site, Downloads, Movies • Http: //www. cs. umd. edu/hcil/millionvis

References - General • Jean-Daniel Fekete & Catherine Plaisant, “Interacive Information Visualization of a Million Items”, Info. Vis 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.

References - Treemaps • [4] Bederson et al. , “Ordered and Quantum Treemaps: Making Effective Use of 2 D 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.