1. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning1 Part II Chapter 9: Topological Path Planning

2. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning2 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?

3. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning3 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

4. 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

5. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning5 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!

6. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning6 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

7. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning7 Example Landmarks

8. 9 floor plan relational graph Relational Methods Nodes: landmarks, gateways, goal locations Edges: navigable path Gateway is an opportunity to change path heading

9. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning9 Problems with early relational graphs Not coupled with how the robot would get there Shaft encoder uncertainty accumulates

10. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning10 Kuipers and Byun: Spatial Hierarchy

11. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning11 Distinctive Places (recognizable, & at least locally unique) Local control strategies (behaviors to get robot between DPs) Distinctive Place Approach

12. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning12 Hill climbing algorithm Directs the robot around in the neighborhood until a measurement function indicates that the robot is at a position where the feature values are maximized the point where it happens is the distinctive place, the algorithm always chooses the next step which is the highest (without looking ahead) the robot always moves in the direction which causes increase in the measurement function

13. 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 Uses one behavior until sees the DP (exteroceptive cueing) then swaps to a landmark localization behavior

14. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning14 Advantages and disadvantages Distinctive place concept eliminates any navigational errors at each node supports discovery of new landmarks as the robot explores an unknown environment distinctive places may be hard to find problems with perception learning local control strategy is hard problems with indistinguishable locations

15. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning15 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

16. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning16 Associative Methods Create a behavior which converts sensor observations into the direction to go to reach a particular landmark that landmark has to have two attributes - 1. Perceptual stability - close views of a landmark are similar 2. Perceptual distinguishibility - far away views are different

17. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning17 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 Randal Nelson, URochester Daryl Lawton, Advanced Decision Systems

18. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning18 Image Signatures The worldTesselated (like faceted-eyes) Resulting signature for home

19. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning19 Move to match the template

20. 9 tree building radio tower mountain OR1 OR2 Metric Map Topological Representation as Orientation Regions

21. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning21 Associative Methods Vehicle can directly perceive when it has entered a new orientation region, by sensing the transition through landmark- pair boundary a set of angles recorded at a point along the path is called a viewframe advantages - tight coupling of sensing to homing, - image signature and viewframe do not require explicit recognition of a landmark disadvantages - require massive storage, - are brittle in the presence of a dynamic world

22. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning22 Case Study Representation - topological map as an ASCII file in Backus-Naur form, the world is orthogonal three node types - room, hall and foyer the map does not show if a corridor is blocked outside of each door is marked cartographer construct the route using Dijkstra shortest path algorithm task manager uses the route to select appropriate abstract navigation behavior (ANB) Sequencing of behaviors based on current perception (releasers) and subgoal

23. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning23 R3->R7 Hd nodes because Have different perception

24. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning24 Transition Table TO FROMHFRHd HNavigate- Hall UndefinedNavigate- Hall F Navigate- Foyer Navigate- Door RUndefinedNavigate- door HdNavigate- hall Navigate- door Navigate- hall

25. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning25 Task manager Not all combinations of nodes are permitted table not necessarily symmetric ANB uses information from the database entries corresponding to nodes as parameters for instantiating the script to the current waypoint pair, in case of a blocked path TM terminates the currently active ANB, directs the robot to the last known node and request from the cartographer a new path from this node to the destination

26. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning26 Execution Exception subscript

27. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning27 Navigation Scripts Switch(door) case door-not-found: //initialization phase //follow wall until find door if wall is found wallfollow to door else move-ahead to find a wall case door-found: //nominal activity phase move-through-door(door-location)

28. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning28 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

29. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning29 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

30. 9 Introduction to AI Robotics (MIT Press), copyright Robin Murphy 2000 Chapter 9: Topological Path Planning30 What you should be able to do 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