1. An arrangement to determine physiologic data, position, orientation and/or geometry of an object of interest comprising: an ultrasound unit with one ore more ultrasound transducers, a position detection system and a processing unit, wherein: a) the position detection system detects the position and/or orientation of each of the one or more ultrasound transducers; b) the processing unit calculates physiologic data, position, orientation and/or geometry of the object of interest from ultrasound data provided by the ultrasound unit and from position and/or orientation information provided by the position detection system; c) the processing unit matches a set of one or more reference models representing certain structures of the object of interest to each frame of ultrasound data provided by the ultrasound unit; d) the processing unit gains information from the set of one or more reference models to calculate the physiologic data, position, orientation and/or geometry of the object of interest; and e) the set of one or more reference models comprises more than one reference model, wherein the processing unit gains the information to calculate the physiologic data, position, orientation and/or geometry of the object of interest from a weighted average of the more than one reference model.