Perhaps the most important result from surveying the vast body of literature on mobile robot positioning is that to date there is no truly elegant solution for the problem. The two categories can be further divided into the following subgroups. Odometry has the advantage that it is totally self-contained, and it is always capable of providing the vehicle with an estimate of its position. This method uses gyroscopes and sometimes accelerometers to measure rate of rotation and acceleration. Inertial navigation systems also have the advantage that they are self-contained.
Inertial sensors are thus unsuitable for accurate positioning over an extended period of time.
Another problem with inertial navigation is the high equipment cost. For example, highly accurate gyros, used in airplanes, are inhibitively expensive. This method computes the absolute position of the robot from measuring the direction of incidence of three or more actively transmitted beacons. The transmitters, usually using light or radio frequencies, must be located at known sites in the environment. In this method distinctive artificial landmarks are placed at known locations in the environment.