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Matthew C. Fleenor Roanoke College

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1 Matthew C. Fleenor Roanoke College
Interactive Visualization of Intercluster Galaxy Structures in the Horologium-Reticulum Supercluster Jameson Miller UNC Chapel Hill Cory W. Quammen UNC Chapel Hill Matthew C. Fleenor Roanoke College

2 Data description Galaxy positions in RA-DEC-cz coordinate system
Right-ascension (RA) ~ longitude Declination (DEC) ~ latitude cz – radial dimension (recessional velocity) ~2500 galaxy locations ~30 clusters

3 Domain questions What is the distribution of intercluster galaxies?
Are there large void regions? How many? Does the supercluster have filaments? How do clusters fit into the structure defined by intercluster galaxies?

4 Standard 2D plots

5 Overvieew

6 Prior 3D experience Collaborators viewed data in immersive environment
Got lost – no context

7 Previous interactive tools
Cosmic Explorer [Song1993] SGI Explorer [Christensen1995] PartiView [Levy2001] AstroMD [Gheller2002]

8 What’s missing Ability to group galaxies into structures they define
Voids Filaments Reference axes in all three RA-DEC-cz dimensions

9 Data types Sparse 3D position data Nominal (categorical) data
Intercluster galaxies vs. clusters User-defined groups indicating structure (filament, void boundary) Group 1 Group 2 Intercluster Galaxy Cluster

10 Nominal encoding 3D glyphs Nominal color encoding
Enough screen real estate Distinct shapes encode object type Depth queues from perspective and occlusion Nominal color encoding Group membership Encoded by 10 of 12 colors recommended by Ware2004

11 RA-DEC-cz reference axes
Orientation to dataset Colored with just-noticeably-different color than background Can turn sides, top, and bottom on or off

12 Curved drop lines Explicit connection between galaxies and reference axes Curved to fit RA-DEC-cz coordinate system Allows comparison to standard plots

13 Structure perception Structure-from-motion Torsional rocking Stereo
Strongest shape cue Torsional rocking Structure-from-motion without interaction Stereo Complements other techniques User can control eye-separation parameter

14 Confirmation of analysis
Quantitative analysis shows two separate overdensities Overdensities pop out in visualization ~95% correspondence between grouping by hand and quantitative grouping

15 Positive result Quick identification of void regions
Selection of galaxies along rim defines bounds of void Offline sphere-fitting refines estimation Six voids identified Known clusters reside around voids

16 Negative result Previous 2D plots identified potential filament structure When rotated in 3D, filament is shown to be two separate structures

17 Computation vs. visualization
Voids – could compute Filaments – maybe could compute Visualization helps astronomers know where to focus quantitative analysis

18 Effective techniques User-controlled interaction Torsional rocking
Critical for maintaining viewer orientation Interactive scaling allows snapping between overview of data and local features, giving context when zooming in Home key moves back to a familiar orientation Torsional rocking Rocking aids void definition when far galaxies peek out from closer galaxy View angle optimization Stereo Stereo is helpful for finding galaxies bordering voids Picking with mouse was hampered by stereo Collaborators came across campus to use it!

19 Software Called GyVe (Galaxy Viewer) Built on VTK, Python, and Tkinter
Available at Runs on Windows and Linux

20 Future work Isosurfaces – initial attempt unused
Image processing for identifying voids from density projections Add interactive statistical tools Haptic probes to feel around for structures

21 Acknowledgements NSF Grant AST 04-06443 (Fleenor) James A. Rose
Russell M. Taylor II

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