1. A method comprising: receiving three-dimensional image data of an imaged object that comprises at least a first rigid part and a second rigid part, wherein the first and the second rigid parts are movably connected to each other, wherein the three-dimensional image data represent a region of the imaged object containing the first rigid part and the second rigid part while the first and the second rigid parts are in a first state of position and orientation relative to each other, identifying sub-regions corresponding to the first and second rigid parts within the three-dimensional image data and dividing the three-dimensional image data into at least first image data of a first sub-region representing the first rigid part and second image data of a second sub-region representing the second rigid part, receiving a set of two-dimensional projection images of the imaged object, wherein the set of two-dimensional projection images comprises at least one image taken in a first projection direction and at least one image taken in a second projection direction, the first and second projection directions being different projection directions, wherein the set of two-dimensional projection images represents a region of the imaged object containing the first rigid part and the second rigid part while the first and the second rigid parts are in a second state of position and orientation relative to each other that is different from the first state, and using a processing device, registering the first image data of the first sub-region with the set of two-dimensional projection images thereby obtaining first registration information, separately registering the second image data of the second sub-region with the set of two-dimensional projection images thereby obtaining second registration information, and determining the position and orientation of the first and second rigid parts relative to each other according to the second state using the first and the second registration information.