A method of navigating along a biological object with a lumen represented by a three-dimensional volume data set comprises generating a plurality of navigation segments connectable in a sequence, each segment having a start point within the lumen, a direction and a length. The navigation may be used for a camera in a virtual endoscopic examination, for example. The direction of each segment is determined by casting groups of rays outwards from the start point of the segment to the object wall, and calculating an average ray length for each group. The group having the largest average ray length is selected, and the axial direction of this group is used as the direction for the segment. The average ray lengths of the groups may be weighted using the direction of the previous segments to bias the navigation generally forward, or may be weighted using a view direction of the camera to allow a user to turn the camera into a chosen branch in the object.