Apparatus and method for estimating a physical state of a movable object

An apparatus for estimating a physical state of a movable object comprises a processor receiving or determining a probability mass function including probabilities for each of a first group of at least two movement classes, wherein the movement models of the first group being determined using sensor data from the inertial measurement unit. The processor receives at least one additional probability mass function associated with a second group of at least two movement classes, wherein the additional probability mass function has been obtained using additional information different from the sensor data. The processor combines the probability mass function and the at least one additional probability mass function to obtain a combined probability mass function over the movement classes of the first group and the second group, selects a movement class having the highest probability from the combined probability mass function, and estimates the physical state of the movable object using a movement model of the selected movement class. Each movement class is either a movement state or a movement model.