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