Light stripers

Light stripers

Light striping, light stripers or structured light detectors work by projecting a
colored line (or stripe), grid, or pattern of dots on the environment. Then a
regular vision camera observes how the pattern is distorted in the image. For
example, in Fig. 6.26a, the striper projects four lines. The lines should occur
at specific, evenly spaced rows in the camera image if the surface is flat. If
the surface is not flat, as shown in Fig. 6.26b, the lines will have breaks or

discontinuities. A vision algorithm can quickly scan each of the designated

rows to see if the projected line is continuous or not. The location of the

breaks in the line give information about the size of the obstacle. The vision

algorithm can also look for where the dislocated line segments appears, since

the distance in image coordinates is proportional to the depth of the object.

The relative placement of the lines indicates whether the object is above the

ground plane (an obstacle) or below (NEGATIVE OBSTACLE a hole or negative obstacle). The more

lines or finer-grained grid, the more depth information.

Light stripers are less expensive formany reasons. First, since they are producing

a line or pattern to be measured, expensive time-of-flight detectors

are unnecessary. The detection is done by the camera. Second, producing a

thick line that can be detected by a camera does not require a laser. Instead it

can be done with structured light, an optical method which allows “regular”

light to mimic desirable properties of laser light. Finally, light stripers pro-