Fast Volume Deformation Using Inverse-Ray-Deformation and FFD

In this paper we present a new approach for free-formdeformation of volume object. Free-form-deformation (FFD) is used as method for calculating the deformation. Rendering is based on the inverse deformation of viewing rays using approaches adapted from Barr [1] and Kurzion [10]. Thus this new approach doesn’t suffer from the overhead of the intermediate step to reconstruct the deformed volume as traditional approaches do. Compared to these earlier methods we integrated algorithmic optimization like distance-coding based space-leaping and early-ray-termination. This is achieved by approximating the deformed viewing rays with polylines and by treating the linear segments as conventional rays. The performance of this optimized rendering method depends on the length of the ray segments. The higher the local curvature, the smaller the segment length which is determined automatically during rendering. For semi-transparent volumes we thus achieve speedups of the optimized algorithm vs. the non-optimized algorithm between 3.13 and 4.43. In the case of opaque objects and empty space in-between the speedup decreases from 14.16 of non-deformed volumes to 4.52 for severely deformed volumes. Thereby the decrease of speedup is mainly determined by less efficient space-leaping due to shorter segments in the polylines.