1. A method for separating a 3D liver object, comprising: displaying the 3D liver object and selected associated vascular and other anatomic structures in a 3D space rendered on a 2D display screen; placing one or more 3D separating surfaces in the 3D space based on automatically or interactively segmented anatomic structural landmarks, where each of the one or more 3D separating surfaces intersects with the 3D liver object at a corresponding 3D pose; separating the 3D liver object into at least two sub-segments based on the one or more 3D separating surfaces, wherein each of the 3D separating surfaces can be independently adjusted directly in the 3D space, in real-time, and interactively by a user based on 3D and/or 2D information related to the 3D liver object, and the selected associated vascular and other anatomic structures.