Hardware assisted volume rendering of unstructured grids by incremental slicing

Some of the more important research results in computational science rely on the use of simulation methods that operate on unstructured grids. However, these grids, composed of a set of polyhedra, introduce exceptional problems with respect to data visualization. Volume rendering techniques, originally developed to handle rectangular grids, show significant promise for general use with unstructured grids as well. The main disadvantage of this approach, compared to isosurfaces, particles or other visualization tools is its non-interactive performance. We describe an efficient method for rendering unstructured grids that is based on incremental slicing and hardware polygon rendering. For a given view direction, the grid vertices are transformed to image space using available graphics hardware. We then incrementally compute the 2D polygon-meshes that result from letting a set of planes, parallel to the screen plane, intersect (slice) the transformed grid. Finally, we use the graphics hardware to render (interpolate-fill) the polygon-meshes and composite them in visibility order. We show that, in addition to being faster than existing methods, our approach also provides adaptive control and progressive image generation. The adaptive method provides user control to ensure that the contribution of every cell is included in the final image or to limit the number of cells that are missed.