Page 256 - Introduction to AI Robotics

6.7 Range from Vision

a. b. 239

Figure 6.27 Lidar images from an Odetics LADAR camera: a.) range and b.) in-
tensity. (Images courtesy of University of South Florida and Oak Ridge National
Laboratory.)

The Sojourner Mars rover used a light striping system for obstacle avoid-
ance. The system projected five lines ahead of the vehicle. 134 This worked
well because Mars has little color or light diversity. Interestingly enough, the
light striper used one member of a stereo pair, but unlike the Marsokhod,
Sojourner did not use stereo for navigation. Instead, the robot would period-
ically take a stereo pair for reconstruction and map-making on Earth.

6.7.3 Laser ranging

Ultrasonics introduces acoustic energy into the environment and measures
the time of flight of the signal to return. The same principle can be used with
lasers; a laser beam can emitted and then the reflectance measured. Unlike a

sonar beam which has a very wide field of view (almost 30 ), a laser produces
an almost infinitesimal field of view. If the laser is directed in a scan, just like
arasterscanon a CRT,the devicecan covera reasonablearea and produce
an image, where the image function produces depth values. Devices which
LASER RADAR use lasers to produce a depth map or image are often called laser radar, ladar,
LADAR or lidar. They can generate up to one million range pixels per second, 52 with
LIDAR
a range of 30 meters and an accuracy of a few millimeters. The mechanical