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“Visibility-based Probabilistic Roadmaps for Motion Planning” Siméon, Laumond, Nissoux. Presentation by: Mathieu Bredif CS326A: Paper Review Winter 2004. Motivation. Save computation time without sacrificing coverage and connectivity. Visibility PRM is an optimized variation of basic PRM.
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“Visibility-based Probabilistic Roadmaps for Motion Planning” Siméon, Laumond, Nissoux Presentation by: Mathieu Bredif CS326A: Paper Review Winter 2004
Motivation • Save computation time without sacrificing coverage and connectivity. • Visibility PRM is an optimized variation of basic PRM
Ensuring Coverage • Visibility Domain of configuration q: • Visibility = • Local planer = • Dynamic Collision • Checking on: • Straight lines • Manhattan paths • Non-holonomic • … q
Ensuring Coverage • Free Space Coverage with Guard nodes Shared Visibility Guard
Ensuring Coverage • Free Space Coverage with Guard nodes Shared Visibility Guard
Creating Connections • Completing roadmap with Connection nodes Shared Visibility Guard Connection
Termination criterion • Meanwhile: 1/ntry = estimation of the volume of the subset of the free space not yet covered by visibility domains. • M is max number of failures before the insertion of a new guard node. • (1-1/M) = estimation of the coverage.
Pathological Case • Probability of connection between guard nodes depend on where they are (randomly) placed.
Possible Improvements • It might be nice to have movable guards to prevent pathological case. • Use sampling techniques to find narrow passages (First Paper).
Visibility PRM – Basic PRM comparison • Heavier Node “filtering” process BUT reduction in calls to the local method, from O(n2) to O(n). • Remaining problems of randomly chosen configuration points (inherent to PRM).
Conclusions • Roadmap size is reduced. • Faster Queries • Few potential routes to choose from (good or bad?) • Control of the coverage by (1-1/M) • Computation Costs seem to be lower than with Basic-PRM.