This 3-D map was produced in 1997 by a stereoscopic vision system. Photos courtesy of Hans Moravec, Carnegie Mellon University.
Robots use sensors to get information about their surroundings.
In general, a sensor measures a characteristic of the environment and makes a proportional electric signal. Many of robot sensors mimic our own senses, but robots can also sense that things we can't, like magnetic fields or ultrasonic sound waves. When light falls on them, they respond by creating or changing an electric signal. Light sensors can also be used for simple navigation. For example, a robot can use them to follow a white line.