Constructive solid geometry and volume rendering
Maurice Termeer · TU/e Research Portal · 2005
Shaded direct volume rendering is a common volume visualization technique. Whenever there is a desire to mask out a part of the volume data set, this technique can be combined with volume clipping. However, the combination of volume clipping with shaded direct volume rendering leads to visible artifacts in the final image if no special care is taken. In this thesis a depth-based volume clipping algorithm is presented that minimizes these artifacts, while maximizing both performance and interactivity. The resulting algorithm allows the clipping volume to be specified as a high-resolution polygon mesh, which has no direct correlation with the volume data. One of the advantages of this method is that both the resolution and orientation of the clipping volume can be modified independently from the volume data set during visualization without a decrease in performance. To achieve a high performance, the possibilities of consumer-level graphics hardware are exploited. The algorithm is integrated into two different ray casting-based shaded direct volume rendering implementations. The first is an existing software-based implementation. The optimizations it contains, both for performance and for image quality, are described, combined with the modifications to support volume clipping. The second volume renderer is a new implementation that uses consumer-level graphics hardware. This volume renderer was developed as a part of this project. Since there are currently very few implementations of ray casting-based volume rendering on graphics hardware, this offers many interesting research possibilities. A number of optimizations specific for ray casting-based volume rendering on graphics hardware are discussed, as well as the integration with the volume clipping algorithm. The result is a volume renderer which is able to offer a trade-off between performance and image quality. A comparison of both volume renderers is given, together with an evaluation of the volume clipping technique.