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Scientific Visualization : From Data to Insight
Vijay NatarajanIndian Institute of Science
Bangalore
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What is Visualization?» http://en.wikipedia.org/wiki/Visualization» Creative Visualization
» “Creative Visualization is the cognitive process of purposefully generating visual mental imagery, with eyes open or closed …”
» … day dreaming
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What is Visualization?
» Visual representation of data (https://en.wiktionary.org/wiki/visualization)
» Data ! Pictures» Scientific Visualization» Scientific (Data) Visualization
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Scientific Data
» Source: Simulations, measurement from imaging devices, sensing devices
» Focus: Scalar dataVijay Natarajan CSA Summer School, July 2017 5
NIR microscopy Density distribution in Silicium
CT / MRI
Electron microscopy
Atomistic simulations(Pore networks)
!
f :D"R
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Scientific Data Visualization» Aim: Study and develop methods to
" Understand underlying phenomena" Communicate (research) findings
» Application domains" medical imaging" x-ray crystallography" structural biology" computational fluid dynamics" climate science" material science" geology, cosmology , …
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CSA Summer School, July 2017 #7
Visualization Pipeline
[dos Santos, S. and Brodlie, K., Gaining understanding of multivariate and multidimensional data through visualization, Computers & Graphics, 28(3), 311–325, 2004.]
Vijay Natarajan
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Visualization : Current Challenges
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» Large data sizes» Feature-rich data» Integrated analysis
and visualization" Visual abstractions" Intuitive exploration
[Doraiswamy and Natarajan, IEEE Trans. Visualization and Computer Graphics, 2013]
vacet.sci.utah.edu
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• Surface plot• interpret scalar value as height
• Color mapping
• assign a color to scalar values
• Contour plot• extract curves as pre-image of given scalar value
Scalar Field Visualization - 2D
!
f :R2 "R
Source: Wikipedia
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IsosurfacePreimage of an isovalue: Isocontours and Isosurfaces
Source: Wikipedia
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Scalar Field Visualization
Isosurfacing for Volume data
Foot from Visible Human Data [US NIH and NLM]
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Isosurfaces
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Isosurfaces
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Isosurfaces
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Isosurfaces
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Isosurfaces
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Isosurfaces
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Isosurface Topology
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Minimum
Maximum
Critical Points
Saddle
Saddle
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Topological Structures : Reeb Graph
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Reeb Graphs
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Georges Henri Reeb
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Contour Tree
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» Loop-free Reeb graph
» Degree-1 and Degree-3
nodes
» How many trees with 1
minimum and 4 maxima?
» 1 minimum and 0 maxima?
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Topological Structures as Abstract Representations
Highlight bones/organs via Reeb graph
[Doraiswamy and Natarajan, IEEE Trans. Visualization and Computer Graphics, 2013]
Pore Networks from MS Complex
[Gyulassy, Natarajan, et al. IEEE Trans. Visualization and Computer Graphics, 2007]
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Mapping to the Volume
» Arcs in Reeb graph map to cylinders in domain» Use Reeb graph as an abstract interface into
scalar volume
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Computing Reeb Graph
» Split-and-compute strategy (2011)• 10 times faster than earlier methods• 4-6 million elements in 4-6 sec
» Parallel algorithm (2015)• 8.6 billion points in 3 min on 64 cores• Requires 10GB only
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Simplification threshold = 0.005 Simplification threshold = 0.01
Simplification + Multiresolution
Input may contain noise or small-sized features
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(Topological) Feature-directed Visualization
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Application 1: Transfer Function Design
Topology controlled volume rendering [Weber et al., IEEE TVCG 2007]
Spatially aware transfer function design
[Doraiswamy and Natarajan, IEEE TVCG 2011]
Movie at 2x
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Application 2: Interactive Exploration of Time-Varying Data
[Doraiswamy and Natarajan, IEEE Trans. Visualization and Computer Graphics, 2011]
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Application 2: Interactive Exploration of Time-Varying Data
[Doraiswamy and Natarajan, IEEE Trans. Visualization and Computer Graphics, 2011]
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Application 3: Segmentation
[Doraiswamy and Natarajan, IEEE Trans. Visualization and Computer Graphics, 2011]
Reeb graph-directed surface segmentation
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Application 4: Isosurface Selection
Extracting and tracking cloud systems[Doraiswamy, Natarajan, and Nanjundiah. IEEE Trans. Visualization and Computer Graphics, 2013]
Flexible isosurfaces[Carr et al., IEEE VIS 2004]
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Application 5: Symmetry in Scientific Data
» Detect similar subtrees within contour tree
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[Thomas and Natarajan, Symmetry in scalar field topology, IEEE TVCG 2011]
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5: Symmetry-aware transfer function design
Adenovirus Ribonucleoprotein Bacteriophage Flagella Bacteriophage
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5: Symmetry-Aware Transfer Function Design
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Acknowledgements
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Visualization and Graphics LabIndian Institute of Science
" Department of Science and Technology, India
" Intel" Robert Bosch Centre for
Cyber-Physical Systems, IISc
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Summary» Challenges in visualization» Feature-directed visualization» Abstract / topology-based representations» Efficient computation of topological structures
" Parallel (GPU / Hybrid) algorithms" Memory efficient
» New applications!!
» Webserver and libraries at http://vgl.csa.iisc.ac.in
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based representations
: VGLIISc