Interactive Navigation in Complex Environments Using Path Planning Salomon et al.(2003) University...
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Transcript of Interactive Navigation in Complex Environments Using Path Planning Salomon et al.(2003) University...
Interactive Navigation in Complex Environments Using Path Planning
Salomon et al.(2003) University of North Carolina
Prepared By Xiaoshan Pan
Content
1st section (3/4)– Pre-compute a global roadmap– Graph search (inigoal) in real-time– Display motion
2nd section (1/4)– User-steered exploration
Basic Idea
Preprocessing phase
Runtime algorithm
Precomputation: Sampling
Gravity
•Shooting rays
Random Rays
Precomputation: Sampling
Gravity
•Shooting rays
ө ө
•Walkable surface
•Construct roadmap
-Max # of samples
-Min dist between samples
•Connectors - Rc > Rg
Rc
Guards & Connectors (C-space)
•Reachability (vs. visibility)
Rg
•Guards - guards can’t see each other
- yes reject c, goto while
c
- no! c becomes a Guard, connect to connectors (if any), goto while
Algorithm (build_roadmap)
While (map_coverage < P_cover), do // map_coverage = guards_reachable/entire_space
Return roadmap
Connector
GuardGuard
Connector
GuardGuard
Connector
GuardGuard
2. Can c be a Connector? See any Guards in Rc? - Yes then connect, goto while (else goto 3)
1. Pick a random config. c
c
3. Can c be a Guard? See any Guards in Rg?
c
Be a Connector Be a Guard Be rejected
Search for a path: init goal Initial position (Rc radius)
ini
goal
Goal position Graph search…
Display Motion: Smooth Path Walk along the path
ini
goal
Smoothing path (cutting redundant corners while walking)
User-steered exploration (local walk)
User has control– A directional vector
Robot always stays on a walkable surface
– In free space– Surface within a tolerance
angle– Steps ok, cliffs NO!!
Robot do not penetrate objects
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
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