Download presentation
Presentation is loading. Please wait.
1
Roadmap Methods How do I get there? Visibility Graph Voronoid Diagram
2
The Roadmap Idea Capture the connectivity of C free in a network of 1-D curves: the roadmap
3
Visibility Graph Method (VGM) Polygonal robot A translating at fix orientation No rotation! Polygonal obstacle in R 2 VGM: construct a semi-free path as a simple polygonal line connecting q init to q goal
4
Main Proposition CB a polygonal region of the plane There exists a semi-free path between q init and q goal There exists a simple polygonal line lying in cl(C free ) with end points q init and q goal and such that its vertices are certices of CB
5
Example q init q goal
6
Visibility Graph - Definition The visibility graph is the non-directed graph G specified as: Nodes: q init, q goal and vertices of CB Edges: 2 nodes connected if either the line segment joining them is an edge of CB, or it lies entirely in C free at endpoints Algorithm of the visibility graph method: 1.Construct visibility graph G 2.Search G for a path from q init to q goal 3.If a path is found, return it; otherwise failure
7
Constructing the VG: Naïve Approach X, X’: q init, q goal or CB vertices If X, X’ endpoints of same edge of CB, then the nodes are connected by a link Otherwise X, X’ are connected by a link iff the line passing through them does not intersect CB Complexity of algorithm O(n 3 )
8
Variation of sweep-line algorithm For each X, compute the orientation i of every half-line from X to another point X i. Sort these orientations. Rotate half-line from X, from 0 to 2 . Stop at each i. At each stop, update intersection with CB Algorithm is O(n 2 logn) Constructing the VG: Improvement
9
Retraction Approach Def.: X a topological space, Y a subspace of X. A surjective map X Y is a retraction iff it is continuous and its restriction to Y is the identity Def.: the retraction preserves connectivity iff for all x X, x and (x) are in the same path- connected component. Proposition: Let :C free R, where R C free is a network of 1D curves, be a CPR. There exists a free-path between q init and q goal iff there exists a path in R between (q init) and (q goal )
10
Voronoid Diagram Def.: let = C free. For any q in C free, let Clearance(q)=min p ||q-p|| Near(q)={p / ||q-p||=clearance(q)} The Voronoid diagram of C free is the set: Vor(C free )={q C free / card(near(q))>1}
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.