As a follow-up to some of the recent discussion about mixing element types, I have forwarded a discussion by Holly Rushmeier from over three years ago on a related matter. You may find it useful.
---------------------- Forwarded by Lloyd A Treinish/Watson/IBM on 12/17/2000 08:13 PM --------------------------- I'm writing in response to one concern about DX, which is its handling of primitive types in finite element meshes. Currently, DX doesn't have support for prisms, or any definite plans to add them. A filter could be readily built to decompose prisms into tetrahedra for the purposes of the interpolation required by modules like "MapToPlane" and to edge lists for using "ShowConnections" to display the original grid. Here is an example: Attached is a file with a cube (i.e. one hexahedron-- a DX "cube" doesn't have to have uniform length sides or perpendicular faces) and with two tetrahedra called "mixed.dx" Note that the cube and tetrahedra share the same positions and data components so that they use consistent values. MapToPlane can be used to get a shaded display of a plane passing through both element types (as shown in the attached gif "smoothin.gif". The cube has grey edges, the tetrahedra have yellow edges, data values are shown with colored filled circles). Since MapToPlane is just displaying Gouraud shaded triangles, there can be shading discontinuities between the region in the cube and the tets, as shown in "disconti.gif". This is an artifact of the plane through the elements being discretized into triangles independently for each element as shown in "discreti.gif". Since these discontinuities are tied to the resolution of your grid, and only show up when there are significantly different colors assigned to adjacent vertices, its not clear to me that they are a problem. Also, I don't know that any other products would give a different result (i.e. would attempt to avoid the mid-edge vertex that gives the shading discontinuity.) -- Holly Rushmeier
discreti.gif
Description: GIF image
disconti.gif
Description: GIF image
smoothin.gif
Description: GIF image
mixed.dx
Description: Binary data
