An Advanced Evenly-Spaced Streamline Placement Algorithm

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ADVESS
An Advanced Evenly-Spaced Streamline Placement
Algorithm
Zhanping Liu Robert J. Moorhead II Joe
Groner Visualization Analysis and Imaging
Lab High Performance Computing Collaboratory Missi
ssippi State University
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Outline
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Introduction
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Introduction

• Evenly-Spaced Streamlines (ESS)

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Introduction

• Evenly-Spaced Streamlines (ESS)

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Introduction

• Evenly-Spaced Streamlines (ESS)

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Introduction

• Evenly-Spaced Streamlines (ESS)

• Four problems with ESS placement generation

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Introduction

• Evenly-Spaced Streamlines (ESS)

• Four problems with ESS placement generation

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Introduction

• Evenly-Spaced Streamlines (ESS)

• Four problems with ESS placement generation

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Introduction
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Introduction
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ADVESS
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ADVESS

• Accelerating Placement Generation

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ADVESS
streamlets shown in red encroach inward near the
field boundaries
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ADVESS

• Enhancing Placement Quality

• Adaptive step sizing requires line-clipping
  against boundaries

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ADVESS

• Enhancing Placement Quality

• Double-queue seeding strategy

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ADVESS

• Enhancing Placement Quality

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ADVESS

• Enhancing Placement Quality

• Obtain the local flow variance magnitude about
  convergence divergence
• Map the magnitude to 0, 1 use it to locally
  adjust threshold distance(s)
• The adjusted threshold distance is larger for
  laminar areas and smaller for
• turbulent areas to reduce cavities without
  noticeable uniformity degradation

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ADVESS

• Detecting Streamline Loops rarely mentioned
  in ESS algorithms

• A naïve intra-line inter-sample distance
  checking does not work since
• the distance between any two successive
  samples of a streamline is less
• than the threshold distance and a simplistic
  intra-line inter-sample
• distance checking always terminates advection
  from the beginning

• A loop is a closed streamline or an open but
  tightly spiraling streamline
• A streamline is ill-looping when the distance
  between two successive
• cycles is less than the advection threshold
  distance d_test
• A closed streamline is always ill-looping

• A spiraling streamline is ill-looping when it
  spirals tightly enough and
• then it may be ill-looping as a whole or only
  in part
• The ill-looping part of a streamline (closed or
  spiraling) is what a loop
• detector should be really focused on and the
  ill-looping part does not
• necessarily begin with the seed

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ADVESS

• Detecting Streamline Loops so far without a
  robust solution for ESS

• A strategy using seed-based inter-sample
  distance checking does not
• work regardless of the use of a seed-based
  curve length or accumulated
• angle as a threshold to begin such kind of
  distance checking

• Our principle is to allow the ill-looping part
  of a streamline to advect
• as long as within a one-cycle limit and this
  encourages a closed
• streamline to form the first cycle and a
  spiraling streamline to show
• the structure in more detail without
  cluttering the placement
• Our universal, effective, and robust strategy
  is to perform both distance
• checking and ill-looping angle checking on
  each existing sample against
• the current sample (NOT the seed) to see
  whether or not the ill-looping
• part approaches the one-cycle limit and is
  going to cause loop problems

• The use of dot-product for ill-looping angle
  representation, cell-based
• inter-sample distance checking for saving the
  approach-the-one-cycle-
• limit judgment, and sample-stamp checking for
  skipping unnecessary
• inter-sample distance checking makes our
  strategy a fast solution

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Results
a loop-free comparison
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ESS placements generated using our ADVESS
algorithm
ESS placements generated using Jobard-Lefers
algorithm
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ESS placements generated using our ADVESS
algorithm
ESS placements generated using Mebarki et als
algorithm
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Results
Three Algorithms in Comparison
Three Algorithms in Comparison
When considering loop-related issues, our
ADVESS is better in overall placement quality
than Mebarki et als algorithm as we will
demonstrate
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without loop detection ? excessive samples
are generated due to ill-looping streamlines
? more distance checking is needed for them ?
more time consumed
Results
ADVESS adopts an effective, robust, and fast loop
detector
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Hawaii islands
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Results
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Conclusions

• ADVESS is capable of interactive placement of
  evenly-spaced streamlines
• RK4-ASSEC allows rapid but accurate streamline
  advection, which is
• critical to the fast and robust loop
  detection strategy
• CHPI provides a fast and flexible
  curve-sampling scheme to generate evenly-
• spaced samples along a streamline for
  inter-sample distance control
• The use of a large sampling size for CHPI
  considerably reduces the amount of
• distance checking while maintaining
  acceptable uniformity
• A double-queue seeding strategy helps preserve
  important flow structures and
• favors long streamlines in an ESS placement
• Adaptive distance control exploits flow
  characteristics to reduce cavities and
• discontinuities by context-sensitively
  adjusting inter-line threshold distance
• An effective, robust, and fast loop detector
  is capable of handling complex flow
• fields without cluttering an ESS placement
• ADVESS is an order-of-magnitude faster than
  Jobard-Lefers algorithm with
• better placement quality
• ADVESS is over five times faster than Mebarki
  et als algorithm with
• comparable placement quality but with more
  robust loop detection

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Conclusions
ADVESS
Welcome to Our ADVESS
Open to Your Advice
Any Questions?
Thank you!