SO FAR, THIS BOOK HAS MAINLY DISCUSSED a traditional and widelyused approach to GPU-based volume rendering that uses a 2D proxy geometry to sample the underlying 3D data set (see, in particular, Chapter 3 on basic GPU-based volume rendering for details on this approach). The predominant proxy geometries are either view-aligned slices (through a 3D texture) or axis-aligned slices (oriented along a stack of 2D textures). Slice-based volume rendering owes its success and popularity to a number of important reasons:

• a high bandwidth between texture memory and rasterization unit, • built-in interpolation methods for a fast resampling (bilinear for

stacks of 2D textures or trilinear in 3D textures), and

• a high rasterization performance. Moreover, the core rendering routines are quite simple to implement.