Mobile Robotics, 2nd Edition

5Instantaneous Localization

Localization consists of finding the position of the robot (i.e. the coordinates of its center as well as its orientation), or more generally all its degrees of freedom. This problem is encountered in navigation, where we need to approximate the position, orientation and speed of the robot. The problem of localization is often considered to be a particular case of state estimation, which will be presented in the following chapters. However, in the case where an accurate state model is not available for our robot, an instantaneous localization often remains possible and may be sufficient for making a decision. Let us take, for instance, the situation in which we are aboard a ship and have just detected a lighthouse, whose absolute position and height are known. By measuring the perceived height of the lighthouse and its angle relative to the ship, we may deduce the position of the ship using a compass and this, without using a state model for the ship. Instantaneous, or model-free localization is an approach to localization that does not utilize the evolution equation of the robot, i.e. it does not seek to make the measures coherent through time. This localization mainly consists of solving equations of geometric nature which are often nonlinear. The variables involved may be position variables or kinematic variables such as speed or accelerations. Since these localization methods are specific and quite far from state estimation methods, we will devote ...