The AIS 3D Laser Range Finder

The AIS 3D laser range finder (Figure 1, top middle) [#!ICAR2003!#,#!ISR2001!#] is built on the basis of a 2D range finder by extension with a mount and a standard servo motor. The 2D laser range finder is attached in the center of rotation to the mount for achieving a controlled pitch motion. The servo is connected on the left side (Figure 1, top middle). The 3D laser scanner operates up to 5h (Scanner: 17 W, 20 NiMH cells with a capacity of 4500 mAh, Servo: 0.85 W, 4.5 V with batteries of 4500 mAh) on one battery pack.

Figure: Top row: The autonomous mobile robot Kurt3D equipped with the 3D scanner. The AIS 3D laser range finder. Its technical basis is a SICK 2D laser range finder (LMS-200). Top Right: Scanned scene as point cloud (viewing pose 1 meter behind scan pose). Reflectance values (distorted view: One scan line of the figure corresponds to a slice of the 2D scanner [#!ISR2001!#]). Bottom row: Input images used for object learning (negative and positive examples for learing the object ``office chair''). Undistorted rendered view as reflectance and depth image (range values are encoded by grey values).

The area of $180^{\circ}\mbox{(h)} \times 120^{\circ}\mbox{(v)}$ is scanned with different horizontal (181, 361, 721 pts.) and vertical (210, 420 pts.) resolutions. A plane with 181 data points is scanned in 13 ms by the 2D laser range finder (rotating mirror device). Planes with more data points, e.g., 361, 721, duplicate or quadruplicate this time. Thus, a scan with 181 $\times$ 210 data points needs 2.8 seconds. In addition to the distance measurement, the 3D laser range finder is capable of quantifying the amount of light returning to the scanner. Figure 1 (top right) shows a scanned scene as point cloud with a viewing pose one meter behind the scan pose, and the reflectance image (bottom left) of this scene. After scanning the 3D data points are projected by an off-screen OpenGL-based rendering module onto an image plane to create a 2D images. The camera for this projection is located in the laser source, thus all points are uniformly distributed and enlarged to remove gaps between them on the image plane. Figure 1 (bottom row) shows a reflectance images and rendered depth images, with distances encoded with grey values.