Ray casting free-form deformed-volume objects

A collection of techniques is developed in this paper for ray casting free-form deformed-volume objects with high quality and efficiency. The known inverse ray deformation approach is combined with free-form deformation to bend the rays to the opposite direction of the deformation, producing an image of the deformed volume without generating a really deformed intermediate volume. The local curvature is estimated and used for the adaptive selection of the length of polyline segments, which approximate the inversely deformed ray trajectories; thus longer polyline segments can be automatically selected in regions with small curvature, reducing deformation calculation without losing the spatial continuity of the simulated deformation. We developed an efficient method for the estimation of the local deformation function. The Jacobian of the local deformation function is used for adjustments of the opacity values and normal vectors computed from the original volume, guaranteeing that the deformed spatial structures are correctly rendered. The popular ray casting acceleration techniques, like early ray termination and space leaping, are incorporated into the deformation procedure, providing a speed-up factor of 2.34-6.56 compared to the nonoptimized case. Copyright (C) 2003 John Wiley Sons, Ltd.