Volume rendering of unstructured hexahedral meshes

摘要

Important engineering applications use unstruc tured hexahedral meshes for numerical simulations. Hex ahedral cells, when compared to tetrahedral ones, tend to be more numerically stable and to require less mesh refine ment. However, volume visualization of unstructured hex ahedral meshes is challenging due to the trilinear variation of scalar fields inside the cells. The conventional solution consists in subdividing each hexahedral cell into five or six tetrahedra, approximating a trilinear variation by a nonadap tive piecewise linear function. This results in inaccurate im ages and increases the memory consumption. In this paper, we present an accurate ray-casting volume rendering algo rithm for unstructured hexahedral meshes. In order to cap ture the trilinear variation along the ray, we propose the use of quadrature integration. A set of computational experi ments demonstrates that our proposal produces accurate re sults, with reduced memory footprint. The entire algorithm is implemented on graphics cards, ensuring competitive per formance. We also propose a faster approach that, as the tetrahedron subdivision scheme, also approximates the tri linear variation by a piecewise linear function, but in an adaptive and more accurate way, considering the points of minimum and maximum of the scalar function along the ray.