But programming those robots to know where they are and how to get to their next location can be complicated and expensive. Engineers at Evolution Robotics, Pasadena, Calif. (evolution.com), have devised a simpler method for low-margin, high-volume users, the NorthStar system of hardware and software. An LED-based projector beams pairs of blinking IR spotlights onto the ceiling or any other surface of a facility. Each spot is encoded with a unique identification code. A detector mounted on the robot detects two or more of these spots and triangulates its position and heading (assuming a relatively flat floor). The detectors have a 120° field of view. So in an area with 8-ft ceilings, it takes a pair of spots to cover a 26-ft circular area or a room 18 18 ft square. Range depends on ceiling height, but for an 8-ft ceiling, the detector can extract heading and position 13 ft from room center, assuming the pair of spots are near the center of the ceiling. Accuracy when the robot's odometer is used, is on the order of 6 in. for position and 2° for heading. There's no limit on the number of detector-equipped robots that can simultaneously use the same spots. A detector sends position, heading, what spots it is using (which can identify the room it is in), and the light intensity of up to 20 spots using serial communication protocol. Robots can record positions and return to them later or record obstacles and avoid them.