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Prepared By Xiaoshan Pan

Interactive Navigation in Complex Environments Using Path Planning Salomon et al.(2003) University of North Carolina. Prepared By Xiaoshan Pan. Content. 1 st section (3/4) Pre-compute a global roadmap Graph search (ini goal) in real-time Display motion 2 nd section (1/4)

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Prepared By Xiaoshan Pan

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  1. Interactive Navigation in Complex Environments Using Path PlanningSalomon et al.(2003) University of North Carolina Prepared By Xiaoshan Pan

  2. Content • 1st section (3/4) • Pre-compute a global roadmap • Graph search (inigoal) in real-time • Display motion • 2nd section (1/4) • User-steered exploration

  3. Runtime algorithm Basic Idea Preprocessing phase

  4. Shooting rays Random Rays Gravity Precomputation: Sampling

  5. Gravity Precomputation: Sampling • Shooting rays • Walkable surface -Max # of samples -Min dist between samples • Construct roadmap ө ө

  6. Rc • Connectors • - Rc > Rg Guards & Connectors (C-space) • Reachability (vs. visibility) • Guards • - guards can’t see each other Rg

  7. 1. Pick a random config. c 2. Can c be a Connector? See any Guards in Rc? - Yes  then connect, goto while (else goto 3) 3. Can c be a Guard? See any Guards in Rg? - no! c becomes a Guard, connect to connectors (if any), goto while - yes  reject c, goto while c c c Algorithm (build_roadmap) While (map_coverage < P_cover), do // map_coverage = guards_reachable/entire_space Return roadmap Be a Connector Be a Guard Be rejected Connector Connector Connector Guard Guard Guard Guard Guard Guard

  8. ini goal Search for a path: init  goal • Initial position (Rc radius) • Goal position • Graph search…

  9. Display Motion: Smooth Path • Walk along the path • Smoothing path (cutting redundant corners while walking) ini goal

  10. User-steered exploration (local walk) • User has control • A directional vector • Robot do not penetrate objects • Robot always stays on a walkable surface • In free space • Surface within a tolerance angle • Steps ok, cliffs NO!!

  11. Local Walk Algorithm • Follow the directional vector, if • - Goal is reached, stop • - Collision, project along obstacle edge • - New surface, step up/down (not a cliff!) • - Edge, step up/down or project along the edge

  12. Discussion • Can deal with complex environment • Because it pre-computes a global roadmap. • Still… • Pre-computation could be time consuming. • Walking along line segments does not look natural. • Overall assessment: Pretty good 

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