Robotic Motion Planning:
A* and D* Search
Robotics Institute 16-735
http://www.cs.cmu.edu/~motionplanning
Howie Choset
http://www.cs.cmu.edu/~choset
16-735, Howie Choset with slides from Ayorkor Mills-Tettey, Vincent Lee-Shue Jr. Prasad Narendra Atkar, Kevin Tantisevi
Outline
• Overview of Search Techniques
• A* Search
• D* Search
• D* Lite
2
Graphs
Collection of Edges and Nodes (Vertices)
A tree
3
Search in Path Planning
• Find a path between two locations in an
unknown, partially known, or known
environment
• Search Performance
– Completeness
– Optimality → Operating cost
– Space Complexity
– Time Complexity
4
Search
• Uninformed Search
– Use no information obtained from the
environment
– Blind Search: BFS (Wavefront), DFS
• Informed Search
– Use evaluation function
– More efficient
– Heuristic Search: A*, D*, etc.
5
Uninformed Search
Graph Search from A to N
BFS
6
Informed Search: A*
Notation
• n → node/state
• c(n1,n2) → the length of an edge
connecting between n1 and n2
• b(n1) = n2 → backpointer of a node n1 to a
node n2.
7
Informed Search: A*
• Evaluation function, f(n) = g(n) + h(n)
• Operating cost function, g(n)
– Actual operating cost having been already traversed
• Heuristic function, h(n)
– Information used to find the promising node to traverse
– Admissible → never overestimate the actual path cost
Cost on a grid
8