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Corrections to the Surface Area Metric with Respect to Mail-Boxing

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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Corrections to the Surface Area Metric with Respect to Mail-Boxing

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  1. Corrections to the Surface Area Metric with Respect to Mail-Boxing Warren Hunt

  2. 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)

  3. What is Mail-boxing? • Optimization for partitioning based acceleration structures • Attempts to avoid multiple intersection tests between the same ray/object pair

  4. 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

  5. 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!

  6. 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

  7. 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!)

  8. KD-Tree Split Plane Left BV Right BV Example: Abutted Cells 1 1 1

  9. KD-Tree Split Planes Left BV Right BV KD-Tree Split Plane Example: Overlapping Cells 2Δ 1-Δ • Original SAM wouldn’t allow either of these splits! • Detailed explanation in the paper 1

  10. 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

  11. Specific Results Teaser • Using an interactive ray-tracer

  12. 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

  13. Questions?

  14. Advertisement! • I’m graduating this fall and looking for a job! • Formally as of now • Willing to relocate etc.

  15. Perspective Questions?

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