“Visibility-based Probabilistic Roadmaps for Motion Planning” Siméon, Laumond, Nissoux Presentation by: Eric Ng CS326A: Paper Review Spring 2003

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: 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 Connection Shared Visibility Guard

Implementation Strategy

Pathological Case Probability of connection between guard nodes depend on where they are (randomly) placed.

Remarks about Visibility PRM [1/2] Node “filtering” process is heavier than Basic PRM, but gains from reduction in calls to the local method, from O(n 2 ) to O(n). It doesn’t solve the problem inherent to PRM, due to randomly chosen configuration points. But allows for faster computation if it does find a path. M is max number of failures before the insertion of a new guard node. The more complex the C- space, the larger M is necessary to provide suitable coverage.

Remarks about Visibility PRM [2/2] The more complex the the C-space, the more advantageous it is for the V-PRM. Because of fairly quick calculations, this algorithm can be done on-the-fly to generate new paths if new information is processed.

Conclusions Roadmap is more compact. –Faster computation –Few potential routes to choose from (good or bad?) It might be nice have movable guards to prevent pathological case. Would improve connectivity issues with narrow passages by integrating higher sampling in problem areas.