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Jameson Miller UNC Chapel Hill. Cory W. Quammen UNC Chapel Hill. Interactive Visualization of Intercluster Galaxy Structures in the Horologium-Reticulum Supercluster. Matthew C. Fleenor Roanoke College. Data description. Galaxy positions in RA-DEC-cz coordinate system

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slide1

Jameson Miller

UNC Chapel Hill

Cory W. QuammenUNC Chapel Hill

Interactive Visualization of Intercluster Galaxy Structures in the Horologium-Reticulum Supercluster

Matthew C. FleenorRoanoke College

data description
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
domain questions
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?
prior 3d experience
Prior 3D experience
  • Collaborators viewed data in immersive environment
  • Got lost – no context
previous interactive tools
Previous interactive tools
  • Cosmic Explorer [Song1993]
  • SGI Explorer [Christensen1995]
  • PartiView [Levy2001]
  • AstroMD [Gheller2002]
what s missing
What’s missing
  • Ability to group galaxies into structures they define
    • Voids
    • Filaments
  • Reference axes in all three RA-DEC-cz dimensions
data types
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

InterclusterGalaxy

Cluster

nominal encoding
Nominal encoding
  • 3D glyphs
    • 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
ra dec cz reference axes
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
curved drop lines
Curved drop lines
  • Explicit connection between galaxies and reference axes
  • Curved to fit RA-DEC-cz coordinate system
  • Allows comparison to standard plots
structure perception
Structure perception
  • Structure-from-motion
    • Strongest shape cue
  • Torsional rocking
    • Structure-from-motion without interaction
  • Stereo
    • Complements other techniques
    • User can control eye-separation parameter
confirmation of analysis
Confirmation of analysis
  • Quantitative analysis shows two separate overdensities
  • Overdensities pop out in visualization
  • ~95% correspondence between grouping by hand and quantitative grouping
positive result
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
negative result
Negative result
  • Previous 2D plots identified potential filament structure
  • When rotated in 3D, filament is shown to be two separate structures
computation vs visualization
Computation vs. visualization
  • Voids – could compute
  • Filaments – maybe could compute
  • Visualization helps astronomers know where to focus quantitative analysis
effective techniques
Effective techniques
  • User-controlled interaction
    • 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!
software
Software
  • Called GyVe (GalaxyViewer)
  • Built on VTK, Python, and Tkinter
  • Available at http://gyve.sourceforge.net/
  • Runs on Windows and Linux
future work
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
acknowledgements
Acknowledgements
  • NSF Grant AST 04-06443 (Fleenor)
  • James A. Rose
  • Russell M. Taylor II
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