Transcript Slide 1

Interactive Visualization of
Intercluster Galaxy Structures in
the Horologium-Reticulum
Supercluster
Jameson Miller
UNC Chapel Hill
1/23
Cory W. Quammen Matthew C. Fleenor
Roanoke College
UNC Chapel Hill
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Data description
• Galaxy positions in RADEC-cz coordinate system
> Right-ascension (RA) ~ longitude
> Declination (DEC) ~ latitude
> cz – radial dimension (recessional
velocity)
• ~2500 galaxy locations
• ~30 clusters
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The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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
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Overvieew
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Prior 3D experience
• Collaborators viewed data in
immersive environment
• Got lost – no context
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Previous interactive tools
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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)
Intercluster
Galaxy
Group 1
Group 2
Cluster
…
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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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The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
RA-DEC-cz reference axes
• Orientation to
dataset
• Colored with justnoticeably-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 RADEC-cz coordinate
system
• Allows comparison
to standard plots
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Structure perception
• Structure-frommotion
> Strongest shape cue
• Torsional rocking
> Structure-from-motion
without interaction
• Stereo
> Complements other
techniques
> User can control eyeseparation 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!
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Software
• Called GyVe (Galaxy Viewer)
• Built on VTK, Python, and Tkinter
• Available at
http://gyve.sourceforge.net/
• Runs on Windows and Linux
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The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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
20/23
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Acknowledgements
• NSF Grant AST 04-06443 (Fleenor)
• James A. Rose
• Russell M. Taylor II
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