Handbook of Robotics Chapter 22 - Range Sensors

1 Range sensors are devices that capture the 3D structure of the world from the viewpoint of the sensor, usually measuring the depth to the nearest surfaces. These measurements could be at a single point, across a scanning plane, or a full image with depth measurements at every point. The benefits of this range data is that a robot can be relatively certain where the real world is, relative to the sensor, thus allowing the robot to more reliably find navigable routes, avoid obstacles, grasp objects , act on industrial parts, etc. This chapter introduces the main representations for range data (point sets, triangulated surfaces, voxels), the main methods for extracting usable features from the range data (planes, lines, triangulated surfaces), the main sensors for acquiring it (Section 22.1-stereo and laser triangulation and ranging systems), how multiple observations of the scene, e.g. as if from a moving robot, can be registered (Section 22.2) and several indoor and outdoor robot applications where range data greatly simplifies the task (Section 22.3). Here we present: 1) the basic representations used for range image data, 2) a brief introduction to the main 3D sensors that are less commonly used in robotics applications and 3) a detailed presentation of the more common laser-baser range image sensors. Range data is a 2 1 2 D or 3D representation of the scene around the robot. The 3D aspect arises because we are measuring the (X, Y, Z) coordinates of one or more points in the scene. Often only a single range image is used at each time instance. This means that we only observe the front sides of objects-the portion of the scene visible from the robot. In other words, we don't have a full 3D observation of all sides of a scene. This is the origin of the term 2 1 2 D. Figure 22.1a shows a sample range image and (b) shows a registered reflectance image, where each pixel records the level of reflected in-frared light. There are two standard formats for representing range data. The first is an image d(i, j), which records the distance d to the corresponding scene point (X, Y, Z) for each image pixel (i, j). There are several common map-pings from (i, j, d(i, j)) to (X, Y, Z), usually arising from the geometry of the range sensor. The most common image mappings are illustrated in Figures 22.2 and …