Topological Path Planning JBNU, Division of Computer Science and Engineering Parallel Computing Lab Jonghwi Kim Introduction to AI Robots Chapter 9

Chapter Objectives Define the difference between a natural and artificial landmark and give one example of each Given a description of an indoor office environment and a set of behaviors, build a relational graph representation labeling the distinctive places and local control strategies using gateways Describe in one or two sentences : gateway, image signature, visual homing, viewframe, orientation region Given a figure showing landmarks, create a topological map showing landmarks, landmark pair boundaries, and orientation regions

Contents Overview Landmarks and Gateways Relational Methods Associative Methods Case Study of Topological Navigation with a Hybrid Architecture Summary

Overview Route representations fall into one of two approaches : Relational  most popular  giving the robot an abbreviated, “connect the dots” graph-style of spatial memory  use an explicit representation, support path planning  focus on the graph-like representation of spatial memory Associative  better for retracing known paths  focus on coupling sensing with localization

Landmarks and Gateways Landmark  one or more perceptually distinctive features of interest on an object or locale of interest  not necessarily a single  can be a grouping of objects McDonald’s stand of aspen trees

Landmarks and Gateways Landmark  be either artificial or natural  “artificial” and “natural” ≠ “man-made” and “organic” artificial landmark  set of features added to an existing object or locale in order to either support recognition of the landmark or some other perceptual activity

Landmarks and Gateways Landmark natural landmark  configuration of existing features selected for recognition which were not expressly designed for the perceptual activity

Landmarks and Gateways Landmark  must satisfy three criteria Be readily recognizable Support the task dependent activity Be perceivable from many different viewpoints good landmark’s characteristics passive in order to be available despite a power failure should be perceivable over the entire range where the robot might need to see it should have distinctive features, and, if possible, unique feature

Landmarks and Gateways Gateway  an opportunity for a robot to change its overall direction of navigation  critical for localization, path planning, and map making

Relational Methods Relational methods  represent the world as a graph or network of nodes and edges Nodes gateways, landmarks, or goals Edges a navigable path between two nodes can attach additional information – direction(N,S,E,W), approximate distance, terrain type, the behaviors needed to navigate that path

Relational Methods Earliest relational graphs for navigation(Smith and Cheeseman)

Relational Methods Earliest relational graphs for navigation(Smith and Cheeseman)

Relational Methods Relational graphs for navigation(Kuipers and Byun)

Relational Methods Distinctive places  landmark that the robot could detect from a nearby region called a neighborhood

Associative Methods Associative methods  create a behavior which converts sensor observations into the direction to go to reach a particular landmark assumption perceptual stability : that views of the location that are close together should look similar perceptual distinguishability : that views far away should look different

Associative Methods Visual homing  work done by Nelson, and later by Engelson image signature created by partitioning an image into sections possible measurement edge density dominant edge orientation average intensity so on…

Associative Methods Visual homing

Associative Methods Visual homing

Associative Methods QualNav(qualitative navigation)  the ideas from Levitt and Lawton  for outdoor navigation over large distances as part of the Defense Advance Research Projects Agency (DARPA) Autonomous Land Vehicle (ALV) project in the late 1980’s

Associative Methods QualNav(qualitative navigation)

Case Study of Topological Navigation with a Hybrid Architecture  Case study of topological navigation using the SFX architecture in 1994 AAAI Mobile Robot Competition by a team of undergraduates form the Colorado School of Mines

Case Study of Topological Navigation with a Hybrid Architecture  placed in a random room  navigate out of the room and to another room within 15 minutes  be given a topological map  How the topological map was entered the activities of Cartographer  How scripts were used to simplify behavioral management, and the lessons learned

Case Study of Topological Navigation with a Hybrid Architecture Path planning a sample topological map start nodes direction blockages landmark

Case Study of Topological Navigation with a Hybrid Architecture Path planning  Cartographer input : a gateway type, start node, goal node output : a list of nodes representing the best path  preprocessing reclassifying (a hall to door connection as Hd) eliminates extraneous gateways  Task Manager select the appropriate abstract navigation behavior d

Case Study of Topological Navigation with a Hybrid Architecture Path planning

Case Study of Topological Navigation with a Hybrid Architecture Path planning

Case Study of Topological Navigation with a Hybrid Architecture Path planning

Case Study of Topological Navigation with a Hybrid Architecture Path planning

Case Study of Topological Navigation with a Hybrid Architecture Navigation scripts  used to specify and carry out the implied details of the plan  navigate-door ANB

Case Study of Topological Navigation with a Hybrid Architecture  navigate-hall ANB

Case Study of Topological Navigation with a Hybrid Architecture  navigate-foyer ANB

Case Study of Topological Navigation with a Hybrid Architecture Lessons learned critical to build the abstract navigation behaviors out of robust primitives (biggest problem is quality of the primitive behaviors) contention for sensing resource metric distance problem impact of obstacles

Summary Landmarks simplify the ‘Where am I?’ problem Gateways special landmarks which reflect a potencial for the robot to change directions navigation methods  relational distinctive places(nodes), local control strategies(lcs)  associative viewframe