CAVASS Visualization Aspects

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CAVASS -Visualization Aspects

• George Greveraa,b, Jayaram Udupab, Dewey Odhnerb,
  Ying Zhugeb, Andre Souzab, Tad Iwanagab, and
  Shipra Mishrab
• aDepartment of Mathematics and Computer Science,
  Saint Josephs University, 5600 City Avenue,
  Philadelphia, PA 19131
• bMedical Image Processing Group (MIPG),
  Department of Radiology, University of
  Pennsylvania, 423 Guardian Drive, 4th Floor
  Blockley Hall, Philadelphia, PA 19104-6021

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What is CAVASS?

• A CAVA Software System
• What is CAVA?
• Computer Assisted Visualization and Analysis
• So CAVASS is a Computer Assisted Visualization
  and Analysis Software System

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What is CAVASS?

• Next generation of 3DVIEWNIX.
• development started in 1987
• released in 1993
• development dates back to the 70s
• free
• runs on Unix and subsequently Linux
• 60 person years of effort
• distributed to 100s of sites
• basis for over 15 specialized packages/apps
• Why CAVASS?

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Significant, more recent developments

• PC platform matures.
• price spirals downward
• performance increases dramatically
• supplant Unix as the scientific workstation of
  choice
• Network bandwidth greatly increases.
• Useable parallel processing standards are defined
  and become freely available.
• Toolkits such as VTK and ITK become freely
  available.
• GUI concept matures and platform independent
  libraries are developed.

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CAVASS features

• Image processing
• Visualization
• Manipulation
• Analysis
• Of large, multidimensional (at least 3D),
  possibly multimodality, data sets.

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Key CAVASS features

• Built upon our experience with 3DVIEWNIX.
• Leverages the existing 3DVIEWNIX software base
  and user interface.
• Port to Windows and Mac OS with continued support
  for Unix and Linux.
• Implement parallel algorithms for time consuming
  operations.
• Support for stereo rendering.
• Interface to ITK.

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Other CAVASS related presentations

• 6509-66 in Visualization Conference Image
  Processing Aspects
• 6519-07 in PACS Conference Software Overview
• Software Workshop, Sunday at 515PM

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Visualization and CAVASS

• All of the most popular modes of visualization
  are incorporated into CAVASS.
• various 2D slice modes
• reslicing
• MIP
• surface rendering
• volume rendering
• animation

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An example of overlaid slice display in CAVASS on
the Windows operating system.
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3D rendering in CAVASS

• Surface rendering
• Volume rendering

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3D rendering in CAVASS

• Surface rendering
• utilizes digital shell and triangulated shell
  (t-shell) rendering algorithms
• operates 6 to 30 times faster entirely in
  software than hardware-based rendering
• implemented only in sequential and not parallel
  mode (because of their existing high speed)

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3D rendering in CAVASS

• Volume rendering
• based on shell rendering
• implemented in parallel mode
• compared to the implementation in VTK
• CAVASS operates at least as fast as VTK and often
  achieves superior performance by a factor of 1.5
  to 5

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Volume Visualization

• surface rendering
• typically binary
• explicit surface
• geometric primitives

• volume rendering
• employs some classification (transfer) function
• no explicit surface
• no geometry

• shell rendering
• some classification
• fuzzy surface
• surface normals

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Shell Rendering

• Udupa, Odhner, 1991
• binary shell defined
• Udupa, Odhner, 1993
• fuzzy shell defined
• Olstad, Steen, Halaas, 1995
• VLSI architecture for shell rendering
• Carnielli, Falcao, Udupa, 1998
• perspective projection introduced
• Grevera, Udupa, Odhner, 1999
• S/R renders surfaces in software 18 to 31 times
  faster than hardware
• Grevera, Udupa, Odhner, 2000
• S/R renders volumes in software at nearly the
  same speed of volume rendering hardware
• Grevera, Udupa, Odhner, 2001
• T-shell rendering introduced
• software/hardware hybrid
• reduce triangles sent to graphics pipeline
• Grevera, Udupa, Odhner, 2005
• T-shell rendering entirely in software 2-10x
  faster than hardware

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Shell Rendering

• parallel projection
• FTB/BTF voxel projection (no ray casting)
• takes advantage of medical data
• regular, cuboidal nature of voxels
• closed surfaces
• combines surface and volume rendering

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T-shell

• not a decimation method retains full detail
• hardware takes a long time to render the first
  view
• 50-2000 times longer than t-shell rendering
• hardware fails to render more than 6 million
  triangles
• T-shell rendering has no such limitation
• T-shell rendering is about 2-10 times faster than
  the hardware method

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Example of triangulated shell (t-shell) rendering
in CAVASS on the Windows operating system.
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Example of triangulated shell (t-shell) rendering
in CAVASS on the Windows operating system.
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Experimental results
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Description of datasets of varying sizes used in
the comparisons.
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Surface rendering timing comparison for CAVASS
shell rendering (sequential implementation with
and without antialiasing) and surface rendering
as implemented in VTK.
Note Same input triangulated surface.
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Volume rendering timing comparison for sequential
and parallel implementations of CAVASS volume
rendering, VTK ray casting, and VTK 2D texture
mapped volume rendering.
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Portable graphics user interface

• Considered Qt, wxWidgets (formerly wxWindows),
  and FLTK.
• Qt proprietary, closed, fees
• FLTK free but doesnt maintain native
  look-and-feel
• wxWidgets
• one C API for all OSs
• maintains native look-and-feel
• free, open source, multiplatform
• portable support for threads, copy-paste,
  drag-and-drop, print, etc.

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Head mounted display employed by CAVASS for
stereo viewing.
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Parallelism

• Considered
• MPI/OpenMPI
• Message Passing Interface
• OpenMP
• Open specifications for Multi Processing

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Parallelism

• MPI
• free (for both Windows, Linux, and Unix)
• part of base Linux install
• COW (cluster of workstations model)
• leverages existing hardware/computers
• optional, inexpensive network upgrade
• OpenMP
• requires purchase of specialized compilers
• multi-threaded, shared memory parallelism model
• requires purchase of expensive multiprocessor
  systems

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Parallelism recommendation

• CAVASS uses MPI.

YOU ALREADY
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Thanks for your attention!

• CAVASS is available from www.mipg.upenn.edu/cavas
  s.
• Release date July/August 2007.
• The authors gratefully acknowledge NIH grant
  number R01-EB004395-01 for support of this work.

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Other CAVASS related presentations

• 6509-66 in Visualization Conference Image
  Processing Aspects
• 6519-07 in PACS Conference Software Overview
• Software Workshop, Sunday at 545 PM