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

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

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Slide1 l.jpg

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 l.jpg

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

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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?

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Standard 2D plots

Overvieew l.jpg


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Prior 3D experience

  • Collaborators viewed data in immersive environment

  • Got lost – no context

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Previous interactive tools

  • Cosmic Explorer [Song1993]

  • SGI Explorer [Christensen1995]

  • PartiView [Levy2001]

  • AstroMD [Gheller2002]

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What’s missing

  • Ability to group galaxies into structures they define

    • Voids

    • Filaments

  • Reference axes in all three RA-DEC-cz dimensions

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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



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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

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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

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Curved drop lines

  • Explicit connection between galaxies and reference axes

  • Curved to fit RA-DEC-cz coordinate system

  • Allows comparison to standard plots

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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

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Confirmation of analysis

  • Quantitative analysis shows two separate overdensities

  • Overdensities pop out in visualization

  • ~95% correspondence between grouping by hand and quantitative grouping

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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

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Negative result

  • Previous 2D plots identified potential filament structure

  • When rotated in 3D, filament is shown to be two separate structures

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Computation vs. visualization

  • Voids – could compute

  • Filaments – maybe could compute

  • Visualization helps astronomers know where to focus quantitative analysis

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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 l.jpg


  • Called GyVe (GalaxyViewer)

  • Built on VTK, Python, and Tkinter

  • Available at

  • Runs on Windows and Linux

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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

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  • NSF Grant AST 04-06443 (Fleenor)

  • James A. Rose

  • Russell M. Taylor II

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