corrections to the surface area metric with respect to mail boxing
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Corrections to the Surface Area Metric with Respect to Mail-Boxing. Warren Hunt. Introduction. The Surface Area Metric is the most common cost metric for acceleration structures The metric doesn’t account for the effects of mail-boxing (when present). What is Mail-boxing?.

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Presentation Transcript
introduction
Introduction
  • The Surface Area Metric is the most common cost metric for acceleration structures
  • The metric doesn’t account for the effects of mail-boxing (when present)
what is mail boxing
What is Mail-boxing?
  • Optimization for partitioning based acceleration structures
  • Attempts to avoid multiple intersection tests between the same ray/object pair
contribution overview
Contribution Overview
  • Present a correction to the surface area metric for mail-boxing
    • Extremely simple to implement
    • Significant reduction in intersection tests
    • Modest improvement in performance
    • Improves the effectiveness of mail-boxing
the surface area metric
The Surface Area Metric
  • Cost(s) = P(sleft)Cost(sleft) + P(sright)Cost(sright)
  • P is the probability function (based on surface area)
  • During build, cost is estimated by the number of objects overlapping each side
    • Mail-boxing changes this cost!
corrected surface area metric
Corrected Surface Area Metric
  • Cost(s) = P(sleft)*Cost(sleft)+ P(sright)*Cost(sright)- P(sright^left)*Cost(sright^left)
  • P(sleft^right) is the probability that a ray strikes both sides of the split
    • Partition is convex, use ratio of surface areas
  • Cost(sleft^right) is the number of objects that occur on both sides of the split
effects of the modification
Effects of the Modification
  • Fundamentally changes the effectiveness of kd-trees when using mail-boxing
    • Allows splits that the SAH wouldn’t previously allow
    • Allows mail-boxing to fully address the integral duplication problem in kd-trees (explained shortly!)
example abutted cells
KD-Tree

Split Plane

Left BV

Right BV

Example: Abutted Cells

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1

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example overlapping cells
KD-Tree

Split Planes

Left BV

Right BV

KD-Tree

Split Plane

Example: Overlapping Cells

1-Δ

  • Original SAM wouldn’t allow either of these splits!
  • Detailed explanation in the paper

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results
Results
  • ~30% reduction in intersection tests when compared to the uncorrected SAM
  • ~5% reduction in overall render-time
  • ~5% increase in traversal steps
  • Results are fairly consistent between off-line and real-time ray-tracers
specific results teaser
Specific Results Teaser
  • Using an interactive ray-tracer
conclusions
Conclusions
  • Presented a correction to the surface area metric for mail-boxing
    • Extremely simple to implement
    • Significant reduction in intersection tests
    • Modest improvement in performance
    • Improves the effectiveness of mail-boxing
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