Page 227 - Concise Encyclopedia of Robotics

Occupancy Grid
OBJECT RECOGNITION
Object recognition refers to any method that a robot uses to pick something
out from among other things. An example is getting a tumbler from a
cupboard. It might require that the robot choose a specific object, such as
“Jane’s tumbler.”
Suppose you ask your personal robot to go to the kitchen and get you
a tumbler full of orange juice. The first thing the robot must do is find the
kitchen. Then it must locate the cupboard containing the tumblers. How
will the robot pick a tumbler,and not a plate or a bowl,from the cupboard?
This is a form of bin picking problem.
One way for the robot to find a tumbler is with a vision system to identify
it by shape.Another method is tactile sensing. The robot can double-check,
after grabbing an object it thinks is a tumbler,to see whether it is cylindrical
(the characteristic shape of a tumbler).If all the tumblers in your cupboard
weigh the same, and if this weight is different from that of the plates or
bowls,the robot can use weight to double-check that it has the right object.
If a particular tumbler is required, then it will be necessary to have them
marked in some way.Bar coding is a common scheme used for this purpose.
In general,the larger the number of characteristics that can be evaluated,
the more accurate is the object recognition. Size, shape, mass (or weight),
light reflectivity,light transmittivity,texture,and temperature are examples
of variable characteristics typical of everyday objects.
See also BAR CODING, BIN PICKING PROBLEM, LOCAL FEATURE FOCUS, SENSOR FUSION, and
VISION SYSTEM.
OCCUPANCY GRID
An occupancy grid is a graphical rendition of a robotic sonar or radar system.
The region covered by the radar or sonar is broken up into squares, in the
fashion of a rectangular coordinate system. Then each square is assigned
a numerical value according to the probability of its being occupied. These
values can range from 1 (100 percent certainty that the square is not
occupied by an object) through 0 (equal chances that the square is occupied
or unoccupied) to +1 (100 percent certainty that the square is occu-
pied).Alternatively,the percentage probability of occupancy can be denoted,
ranging from 0 (definitely not occupied) to 100 (definitely occupied).
When rendered as a two-dimensional (2-D) figure, an occupancy grid
consists of a set of squares or rectangles, each with a number inside,
representing the probability that the square is occupied. However, an
occupancy grid can be rendered using colors instead of numbers if less
precision is demanded.This technique is often used in meteorological radar
or satellite displays showing intensity of precipitation,wind speed,temper-
atures of cloud tops, or other variables. Probabilities of occupancy might

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