This section elaborates on our methods for navigating quickly through a 3D image. Section 3.1 introduces the ray-casting model used to compute the volume-rendered view at any arbitrary site along the navigation path. Section 3.2 describes the ADRT approach to ray-segment sharing, which results in considerable computational reduction for rendering. In Section 3.3, we discuss the data structure that is accessed and updated for view computation. Finally, Section 3.4 describes the computation needed in updating the data structure and in computing views for different kinds of navigation movements.