We propose a method for visualizing 3-D scalar data defmed on unstructured grid data by means of
tetrahedral primitives. In these primitives, data are distributed linearly not only along edge lines but along
any line segments. This characteristic is well suited to hnëar interpolation, which is a very effective
method of visualization in terms of computational cost.
Because of the wide use of the 3-D fmite element method (FEM), there is a strong need for volume visualization
of the unstructured grid data that is output by 3-D FEM analysis. In this kind of analysis,
various kinds of fmite elements, which are composed of unstructured grid data, are used in a mixed form
to represent a complicated 3-D space. In a finite element, data are expressed by means of the element's
own interpolation function. In terms of data processing, a simple interpolation function is most suitable,
because it consumes few computational resources. We therefore select a linear tetrahedral element (LTE),
and introduce a concept of element subdivision to other fmite elements. In our method, each fmite element
is first reconstructed as a set of LTEs that approximates its interpolation function.
We visualize iso-valued surfaces from 3-D scalar data by using an LTE as a processing primitive. For this,
we have developed two methods. One is a method for extracting triangular facets as iso-valued surfaces
and rendering them by a traditional shading algorithm. The other is a method for rendering LTEs directly
in order to visualize iso-valued surfaces.
We apply these methods to analysis of thermal stress in a semi-conductor chip and simulation of air-flow
in a clean room, and confirm their effectiveness.