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

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 Space-Filling ( Scatter Plot ) ( Treemap )

TreeMap of a Million Items

TreeMap 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 ] ) 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

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 15M tps, achievable in practice only with Δ strips. ) This work done with NVidia GeForce3 cards, 2GHz computers, OpenGL 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 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.

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

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.

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.

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”, 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.

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.