Page 165 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Chapter 11

3
added to the environment for the robot’s purposes . Features that are added to the
environment for navigation purposes are called fiducials or fids. Robot engineers
often refer to the need to add such artificial references as “decorating the environ-
ment,” a phrase of mild derision.

In the days when sonar was the best available sensor technology, the programmer
had no choice but to use the very narrow range of navigation features that sonar could
detect and discriminate. As sensor systems have become more capable, the naviga-
tion features available to robots have become more complex. In many ways, this
development cycle has paralleled the history of modern aircraft navigation, espe-
cially as it accelerated rapidly during World War II.
Here we pick up the story where we left off in Chapter 7. As WWII progressed, the
allies turned the tables and began bombing operations over occupied Europe. Now
the British Royal Air Force (RAF) began experiencing the same heavy losses of
bombers that the Luftwaffe had experienced during the Battle of Britain. Like the
Germans, they switched to night bombing, and they too found accurate navigation
over blacked-out terrain to be very difficult. Since they had defeated the German beam
systems, the British looked for a more robust solution to the navigation problem.

A new downward-looking radar was developed that could show the navigator a
representation of the ground below. Although much of the terrain showed up as a
confusing jumble of blips (like the lidar data in Figure 11.2), some features like rivers
and shorelines stood out clearly. The British thus navigated by dead reckoning until
such an easily recognized feature was reached, and then corrected their position
estimates. Missions were planned to assure that the bombers would fly over an easily
4
recognized feature shortly before they reached their targets .

3 Even data from a GPS receiver is essentially the result of imaging a set of satellites. Most of the
concepts discussed here will thus work if a GPS system is simply considered to be one of the
robot’s sensors.
4 In response to this system, the Germans developed a receiver for their night fighters that could
home in on the radar transmissions of the RAF bombers. This continual game of measures and
countermeasures spurred the ever-faster development of electronic technology. Developments
ranging from microwave ovens to computers and fax machines all have their roots in this incred-
ible period of history.

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