Mobile Robotics

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Mobile Robotics

• Julie Letchner
• Angeline Toh
• Mark Rosetta

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(No Transcript)
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Fundamental Idea Robot Pose

• 2D world (floor plan)
• 3 DOF

Very simple modelthe difficulty is in autonomy
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Major Issues with Autonomy

• Movement
• Inaccuracy

• Sensor
• Inaccuracy

• Environmental
• Uncertainty

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Problem One Localization

• Given

• World map
• Robots initial pose
• Sensor updates

Find

• Robots pose as it moves

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How do we Solve Localization?

• Represent beliefs as a probability density
• Markov assumption
• Pose distribution at time t conditioned on
• pose dist. at time t-1
• movement at time t-1
• sensor readings at time t
• Discretize the density by
• sampling

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Localization Foundation

• At every time step t
• UPDATE each samples new location based on
  movement
• RESAMPLE the pose distribution based on sensor
  readings

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Algorithms

• Markov localization (simplest)
• Kalman filters (historically most popular)
• Monte Carlo localization / particle filters
• Same Sampled probability distribution
• Basic update-resample loop
• Different Sampling techniques
• Movement assumptions

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Localizations Sidekick Globalization

• Localization without knowledge of start location

• Credit to Dieter Fox for this demo

• One step further kidnapped robot problem

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Problem Two Mapping

• Given

• Robot
• Sensors

Find

• Map of the environment
• (and implicitly, the robots location as it
  moves)

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Simultaneous LocalizationAnd Mapping (SLAM)
If we have a map We can localize!
If we can localize We can make a map!
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Circular Error Problem
If we have a map We can localize!
NOT THAT SIMPLE!
If we can localize We can make a map!
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How do we Solve SLAM?

• Incorporate location/map uncertainties into a
  single model
• Optimize robots exploratory path
• Use geometry (especially indoors)

Major hurdle correlation problem

• Credit to Sebastian Thrun for this demo

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For the Interested
Good overview papers by Sebastian
Thrun Probabilistic Algorithms in Robotics,
2000 Robotic Mapping A Survey, 2002
Stanford course cs225B Build a Markov
Localization engine Run it on Amigobots to play
soccer
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Up Next
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