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

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

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-2.cs.cmu.edu/~thrun/3d/

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

Types of 3D Mapping Robots Stationary Move with manual guidance Fully automated