In interactive viewing the differences between subsequent frames are usually small. The C-Buffer approach [58] works by storing, at each pixel location, the object-space coordinates of the first non-empty voxel hit by the corresponding ray. This information is used to estimate the initial position of a ray in the consecutive frame. For each change of viewing parameters, the C-Buffer is transformed accordingly. In the case of rotation, a transformed buffer goes through a process of eliminating coordinates that might have become hidden.