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DESIGN OF A GENERIC PATH PATH PLANNING SYSTEM PowerPoint PPT Presentation


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DESIGN OF A GENERIC PATH PATH PLANNING SYSTEM. AILAB Path Planning Workgroup. OUTLINE. Path Planning Basics Current Implementations System Design Conclusion. PATH PLANNING BASICS. Path Configuration Work Space Configuration Space (Cspace) Cell Decomposition

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DESIGN OF A GENERIC PATH PATH PLANNING SYSTEM

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DESIGN OF A GENERIC PATH PATH PLANNING SYSTEM

AILAB

Path Planning Workgroup


OUTLINE

  • Path Planning Basics

  • Current Implementations

  • System Design

  • Conclusion

AILAB Path Planning Workgroup


PATH PLANNING BASICS

  • Path

  • Configuration

  • Work Space

  • Configuration Space (Cspace)

    • Cell Decomposition

    • Roadmap (Skeletonization)

  • Free, Obstacle, Unknown Space

  • Dimension and Degrees of Freedom

AILAB Path Planning Workgroup


Cell Decomposition

  • Regular Grids

  • Multiresolution Cells

  • Trapezoidal Cells

AILAB Path Planning Workgroup


Roadmap (Skeletonization)

  • Meadow Maps

  • Generalized Voronoi Diagrams

  • Visibility Graphs

  • Probabilistic Roadmaps

AILAB Path Planning Workgroup


Properties of Path Planners

  • Dynamic vs. static

  • Global vs. local

  • Optimal vs. suboptimal

  • Complete vs. heuristic

  • Metric vs. topological

AILAB Path Planning Workgroup


Classification of Obstacles

Category of Obstacles from Arai et. al. [Arai89, 28]

AILAB Path Planning Workgroup


Path Planning Techniques

  • Reactive Methods

    • Artificial Potential Fields

    • Vector Field Histogram Method

  • Graph Traversing Methods

    • A* Algorithm

    • Best First / Breadth First / Greedy Search

  • Wavefront Method

  • Other Methods

    • Wall following, Space filling curves, Splines,Topological maps, etc.

AILAB Path Planning Workgroup


Possible problems of applying ordinary PP methods to MAS are,

Collisions,

Deadlock situations, etc.

Problems with MA-PP are,

Computational overhead,

Information exchange,

Communication overhead, etc.

Problems with MA-PP

AILAB Path Planning Workgroup


Approaches

  • Cenralised: All robots in one composite system.

    +Find complete and optimum solution if exists.

    +Use complete information

    -Exponential computational complexity w.r.t # of robots

    -Single point of failure

  • Decoupled: First generate paths for robots (independently), then handle interactions.

    +Proportional computation time w.r.t # of robots

    +Robust

    - Not complete

    -Deadlocks may occur

AILAB Path Planning Workgroup


Improvements for MA-PP

  • Priority assignment

  • Aging

  • Rule-Based methods

  • Resource allocation

  • Robot Groups

  • Virtual dampers and virtual springs

  • Assigning dynamic information to edges and vertices

    ...

AILAB Path Planning Workgroup


Characteristics of MAS

According to Dudek et. al. [Dudek96,53],

  • Team Size1, 2, limited, infinite

  • Communication RangeNone, Near, Infinite

  • Communication TopologyBroadcast, Addressed, Tree, Graph

  • Communication BandwidthHigh, Motion related, Low, Zero

  • Team CompositionHomogeneous, Heterogeneous

AILAB Path Planning Workgroup


Characteristics of Domain

  • Initial InformationNone, Partial, Complete

  • Number of Targets1, Many

  • Target AvailableTrue (i.e. go to target), False (i.e. explore for target)

  • Stationary TargetsTrue, False

AILAB Path Planning Workgroup


Complexity of Path Planning

  • In 3D work space finding exact solution is NP-HARD. [Xavier92, 54]

  • Path planning is PSPACE-HARD. [Reif79,55]

  • The compexity increases exponentially with,

    • Number of DOF [Canny88, 9]

    • Number of agents

AILAB Path Planning Workgroup


Imperfect solutions

  • Used in case of compex problems,

    • Approximation

    • Probabilistic

    • Heuristic

    • Special cases

AILAB Path Planning Workgroup


CURRENT IMPLEMENTATIONS

  • Sampling Based Algorithms

    • Incomplete, but efficient and practical

  • Types

    • Multiple Query

    • Single Query

AILAB Path Planning Workgroup


Multiple Query

  • A map is generated for multiple queries

  • Fill the space adequately

  • Probabilistic Roadmap

    • Uniform sampling of C-free

    • Local planner attempts connections

    • Biased sampling

AILAB Path Planning Workgroup


Single Query

  • Suited for high dimensions

  • Find a path as quick as possible

  • RRTs

    • Grow from an initial state

      • RRT-Connect : Grow from both initial and goal

    • Expand by performing incremental motions

AILAB Path Planning Workgroup


Demos

  • Path Planning

    • Probabilistic Roadmap (PRM)

      • Different sampling methods

    • Rapidly-exploring Random Trees (RRTs)

      • RRT

      • RRT-Connect

AILAB Path Planning Workgroup


SYSTEM DESIGN

* Following slides are based on Lavelle’s Motion Strategy Library, implemented in C++

AILAB Path Planning Workgroup


Overview

MODULES:

  • Model

  • Geom

  • Problem

  • Solver

  • Scene

  • Render

  • Gui

AILAB Path Planning Workgroup


Model

  • Contain incremental simulators that model the kinematics and dynamics of a variety of mechanical systems. The methods allow planning algorithms to compute the future system state, given the current state, an interval of time, and a control input applied over that interval.

AILAB Path Planning Workgroup


Geom

  • These define the geometric representations of all obstacles in the world, and of each part of the robot. The methods allow planning algorithms to determine whether any of the robot parts are in collision with each other or with obstacles in the world.(PQP - the ProximityQueryPackage)

AILAB Path Planning Workgroup


Problem

  • This is an interface class to a planner, which abstracts the designer of a planning algorithm away from particular details such as collision detection, and dynamical simulations. Each instance of a problem includes both an instance of Model and of Geometry. An initial state and final state are also included, which leads to a problem to be solved by a solver (typically a planning algorithm).

AILAB Path Planning Workgroup


Planner

  • The most important module.

  • Base for all path planners...

AILAB Path Planning Workgroup


CONCLUSION

  • Path planning is a challenging task with many different applications.

  • Each application may device its own path planning strategy.

  • A generic path planning library may provide solution or guidelines for other path planners.

  • ...

AILAB Path Planning Workgroup


QUESTIONS?

Thank you...

kaplanke@boun.edu.tr

fuatgeleri@gmail.com

AILAB Path Planning Workgroup


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