3 D Mapping Robots Intelligent Robotics School of
3 D Mapping Robots Intelligent Robotics School of Computer Science Jeremy Wyatt James Walker
What Are 3 D 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 8 m with a resolution of 1 mm and a statistical error of +/-10 mm • 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 3 D 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 3 D 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. 25 m/s • Therefore approximately one scan every 5 cm
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 p 1 and p 2 from the same scan, taken at angles α and α + 0. 5˚ • Choose the two corresponding points q 1 and q 2 from the next scan • Form two triangles p 1 p 2 q 1 and q 1 p 2 q 2 • 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. 52 m 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 omnicam • 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 3 D mapping is and some uses for 3 D mapping • Different types of sensors used • How to collect data and convert it into a 3 D model • Some more advanced methods for 3 D mapping and processing of the data
References • www. cc. gatech. edu/ai/robot-lab/research/3 d/ • www-2. cs. cmu. edu/~thrun/3 d/
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