9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning1 Part II Chapter 9: Topological Path Planning

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning2 Objectives Define the difference between natural and artificial landmarks; 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 for 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

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning3 Navigation Where am I going? Mission planning What’s the best way there? Path planning Where have I been? Map making Where am I? Localization Mission Planner Carto- grapher Behaviors deliberative reactive How am I going to get there?

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning4 Spatial Memory What’s the Best Way There? depends on the representation of the world A robot’s world representation and how it is maintained over time is its spatial memory –Attention –Reasoning –Path planning –Information collection Two forms –Route (or qualitative) –Layout (or metric) Layout leads to Route, but not the other way

9 Route, or Qualitative Navigation Two categories Relational –spatial memory is a relational graph, also known as a topological map –use graph theory to plan paths Associative –spatial memory is a series of remembered viewpoints, where each viewpoint is labeled with a location –good for retracing steps

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning6 Topological Maps Use Landmarks A landmark is one or more perceptually distinctive features of interest on an object or locale of interest Natural landmark: configuration of existing features that wasn’t put in the environment to aid with the robot’s navigation (ex. gas station on the corner) Artificial landmark: set of features added to the environment to support navigation (ex. highway sign) Roboticists avoid artificial landmarks!

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning7 Desirable Characteristics of Landmarks Recognizable (can see it when you need to) –Passive –Perceivable over the entire range of where the robot might need to view it –Distinctive features should be globally unique, or at least locally unique Perceivable for the task (can extract what you need from it) –ex. can extract relative orientation and depth –ex. unambiguously points the way Be perceivable from many different viewpoints

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning8 Example Landmarks

9 floor plan relational graph Relational Methods Nodes: landmarks, gateways, goal locations Edges: navigable path Gateway is an opportunity to change path heading

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning10 Problems with early relational graphs Not coupled with how the robot would get there Shaft encoder uncertainty accumulates

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning11 Kuipers and Byun: Spatial Hierarchy

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning12 Distinctive Places (recognizable, & at least locally unique) Local control strategies (behaviors to get robot between DPs) Distinctive Place Approach

9 neighborhood boundary distinctive place (within the corner) path of robot as it moves into neighborhood and to the distinctive place Actually Getting to a Distinctive Place: Neighborhoods Use one behavior until sees the DP (exteroceptive cueing) then swap to a landmark localization behavior

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning14 Class Exercise Create a relational graph for this floorplan Label each edge with the appropriate LCS: mtd, fh Label each node with the type of gateway: de, t, r Room 1Room 2 Room 3 Room 4 r1 r2 de1 de3 de2 r3 r4 t1t2t3fh mtd

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning15 Case Study Representation Sequencing of behaviors based on current perception (releasers) and subgoal Algorithm

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning16 R3->R7 Hd nodes because Have different perception

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning17 Transition Table TO FROMHFRHd HNavigate- Hall UndefinedNavigate- Hall F Navigate- Foyer Navigate- Door RUndefinedNavigate- door HdNavigate- hall Navigate- door Navigate- hall

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning18 Path Planning Algorithm Relational graph, so any single source shortest path algorithm will work (Dijkstra’s) If wanted to visit all rooms, what algorithm would you use?

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning19 Execution Exception subscript

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning20 Associative Methods Visual Homing –bees navigate to their hive by a series of image signatures which are locally distinctive (neighborhood) QualNav –the world can be divided into orientation regions (neighborhoods) based on perceptual events caused by landmark pair boundaries Assumes perceptual stability, perceptual distinguishability Randal Nelson, URochester Daryl Lawton, Advanced Decision Systems

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning21 Image Signatures The worldTesselated (like faceted-eyes) Resulting signature for home

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning22 Move to match the template

9 tree building radio tower mountain OR1 OR2 Metric Map Topological Representation as Orientation Regions

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning24 Summary Route, qualitative, and topological navigation all refer to navigating by detecting and responding to landmarks. Landmarks may be natural or artificial; roboticists prefer natural but may have to use artificial to compensate for robot sensors There are two type of qualitative navigation: relational and associative

9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning25 Summary (cont.) Relational methods use graphs (good for planning) and landmarks –The best known relational method is distinctive places –Distinctive places are often gateways –Local control strategies are behaviors Associative methods remember places as image signature or a viewframe extracted from a signature –can’t really plan a path, just retrace it –direct stimulus-response coupling by matching signature to current perception