PHD Thesis - Institute for Computer Graphics and Vision - Graz ...

8.2. Map building experiments 132
8.1.2 Laser range finder
The mobile robot is equipped with a SICK LMS-200 laser range finder (LRF). The LRF allows
range measurements with a field-of-view of 180 ◦ . The angular resolution is 0.5 ◦ . Thus in our
configuration we get 360 range measurements per laser reading. The range measurements are
accurate up to +/- 15mm for a range of 1m to 8m. The LRF is mounted at a height of
about 30cm. The robot comes with a laser localization and navigation system, which allows the
creation of accurate maps using the LRF. The software ScanStudio stitches together individual
laser measurements to a global map and performs a final global registration. The such created
maps and robot positions are used as ground truth for the visual localization experiments.
8.1.3 Camera setup
For our experiments the mobile robot has been equipped with a 2-mega-pixel digital camera LU-
205 from Lumenera. The camera features a CMOS sensor and is able to capture color images
with a maximal resolution of 1600 × 1200 pixel. The achieved frame rate for this resolution is
15 frames per second. For our actual experiments we used images with a resolution of 800 × 600
by using the sub-sampling option of the camera.
The camera is equipped with a 4.8mm wide-angle lens. The wide-angle lens has a field-ofview
of about 90 ◦ but introduces already heavy radial distortions. Thus the captured images
have to be re-sampled to remove the radial distortion before further processing. Figure 8.2(a)
shows an image before the radial distortion got removed. Figure 8.2(b) shows the re-sampled
image where the radial distortion got removed. Re-sampling is done with bilinear interpolation.
The radial distortion as well as the principal point and the focal length of the camera setup are
estimated using the calibration toolbox of Bouguet 2 .
(a)
(b)
Figure 8.2: (a) Original image of the camera setup using a wide-angle lens showing heavy radial
distortions. (b) Re-sampled image with radial distortion removed.
8.2 Map building experiments
In the next two sections results for the map building algorithm are shown. One experiment was
carried out in an office room. Another experiment was carried out in a hallway of the university
2 Camera calibration toolbox for Matlab (available at www.vision.caltech.edu/bouguetj/)