3D Mapping Robots
Intelligent Robotics
School of Computer Science
Jeremy Wyatt
James Walker
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
Types of Sensing Techniques
• Stereo vision• Laser range finders• A combination of the two
Stereo Vision
• Use stereo disparities to compute depth
• Inaccurate in detecting the position of walls and objects especially in cluttered environments
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
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
The GATech Robot
• Equipped with a laser range finder positioned vertically to scan perpendicular to the movement of the robot
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
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
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
Collecting the Co-ordinates to Form Triangles
• Choose two scan points p1 and p2 from the same scan, taken at angles α and α + 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
GATech Model
GATech Model
GATech Model
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
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
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
Thrun et al
Thrun et al
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
References
• www.cc.gatech.edu/ai/robot-lab/research/3d/• www-2.cs.cmu.edu/~thrun/3d/
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