3D Mapping Robots

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3D Mapping Robots

• Intelligent Robotics
• School of Computer Science
• Jeremy Wyatt
• James Walker

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What Are 3D Mapping Robots and Their Uses?

• Robots which produce a 3-dimensional model of
  their environment from the data they collect
• They can be used by people who need to know more
  about the interior of a building
• Architects
• Fire fighters
• Human rescue workers

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Types of Sensing Techniques

• Stereo vision
• Laser range finders
• A combination of the two

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Stereo Vision

• Use stereo disparities to compute depth
• Inaccurate in detecting the position of walls and
  objects especially in cluttered environments

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Laser Range Finders

• Very accurate in measuring distances to walls and
  objects in the environment
• Has a range of 8m with a resolution of 1mm and a
  statistical error of /-10mm
• Can not detect any texture in the environment so
  can only produce single coloured models

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A Combination of the Two

• Laser range finders for detecting the distance of
  walls and objects
• An omni-cam for producing texture maps for a
  realistic visualisation of the environment

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The GATech Robot

• Equipped with a laser range finder positioned
  vertically to scan perpendicular to the movement
  of the robot

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How the Robot Builds the 3D Models

• Collects raw data from the environment using the
  laser range finder
• Converts the raw data into Cartesian co-ordinates
• Converts the Cartesian co-ordinates into a mesh
  for the 3D model

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How the Robot Collects the Raw Data

• Laser moves through 180 in 0.5 steps from one
  side of the robot over the top to the other
  recording the distance
• Approximately 38 scans are completed every second
• Robot moves forward at 0.25m/s
• Therefore approximately one scan every 5cm

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Transforming the Raw Data Into Co-ordinates

• Raw data is in the form of cylindrical
  co-ordinates
• Transformed using the pose of the robot, the
  angle of the scan and the height of the centre of
  the laser scanner

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Collecting the Co-ordinates to Form Triangles

• Choose two scan points p1 and p2 from the same
  scan, taken at angles a and a 0.5
• Choose the two corresponding points q1 and q2
  from the next scan
• Form two triangles p1p2q1 and q1p2q2
• For each triangle calculate its normal vector

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GATech Model
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GATech Model
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GATech Model
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Disadvantages of This Approach

• The corridor appears to be slightly curved due to
  the way the robot moves
• Obstacles below a height of 0.52m can not be
  detected by the robot
• No filtering techniques were used so the model is
  very noisy but retains a high level of complexity
  because of this

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Further Examples Thrun et al

• Uses two laser range finders and an omni-cam
• Uses a technique called expectation maximisation
• Processes the data to reduce the noise

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Expectation Maximisation

• Estimates the number of surfaces and their
  location
• Adds and removes surfaces until it converges on
  the best fit model for the data

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Thrun et al
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Thrun et al
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Summary

• Brief overview of what 3D mapping is and some
  uses for 3D mapping
• Different types of sensors used
• How to collect data and convert it into a 3D
  model
• Some more advanced methods for 3D mapping and
  processing of the data

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References

• www.cc.gatech.edu/ai/robot-lab/research/3d/
• www-2.cs.cmu.edu/thrun/3d/

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Processing the Data

• Various techniques and algorithms have been used
  to reduce the noise in the data
• Smoothing is always used as a final post
  processing step as nearby measurements are likely
  to belong to the same surface

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Types of 3D Mapping Robots

• Stationary
• Move with manual guidance
• Fully automated