Page 93 - Concise Encyclopedia of Robotics

Distance Resolution
computer to keep track of the whereabouts of insect robots. There are several
ways for an autonomous robot to measure the distance between itself and
some object.
Sonar uses sound or ultrasound, bouncing the waves off of things
around the robot and measuring the time for the waves to return. If the
robot senses that an echo delay is extremely short, it knows that it is getting
too close to something. Acoustic waves propagate at a speed of roughly
335 m/s in dry air at sea level.
Radar works like sonar, but uses microwave radio signals rather than
sound waves. Light beams can also be used, particularly lasers, in which
case the scheme is called ladar. But radio and light beams travel at such
high speed (300 million m/s in free space) that it is difficult to measure
delay times for nearby objects. Also, some objects reflect light waves
poorly, making it difficult to obtain echoes strong enough to allow dis-
tance measurement.
Stadimetry infers the distance to an object of known height, width, or
diameter by measuring the angle the object subtends in the vision system’s
field of view.
Beacons of various kinds can be used for distance measurement. These
devices can use sound, radio waves or light waves.
See also AUTONOMOUS ROBOT, BEACON, DISTANCE RESOLUTION, INSECT ROBOT, LADAR,
RADAR, SONAR, STADIMETRY, and TIME-OF-FLIGHT DISTANCE MEASUREMENT.
DISTANCE RESOLUTION
Distance resolution is the precision of a robotic distance measurement
system. Qualitatively, it is the ability of the system to differentiate between
two objects that are almost, but not quite, the same distance away from
the robot. Quantitatively, it can be measured in meters, centimeters,
millimeters, or even smaller units.
When two objects are very close to each other, a distance-measuring
system sees them as a single object. As the objects get farther apart, they
become distinguishable. The minimum radial separation of objects, for a
ranging system to tell them apart, is the distance resolution.
With some distance measuring systems, nearby sets of objects can be
resolved better than sets of objects far away. Suppose two objects are
separated radially by 1 m.If their mean (average) distance is 10 m,their sep-
aration is 1/10 (10 percent) of the mean distance. If their mean distance is
1000 m,their separation is 1/1000 (0.1 percent) of the mean distance.If the
distance resolution is 1 percent of the mean distance, then the system can
tell the nearer pair of objects apart, but not the more distant pair.
Distance resolution depends on the type of ranging system used.
The most sensitive methods compare the phases of the wavefronts
emitted by laser beams. These waves either arrive from, or are reflected

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