[vtkusers] vtkQuadraticHexahedron visible edges or wireframe show triangles within the 3D cell faces

[Greg Thorwald]

Hello,

I am using the vtkHexahedron and vtkQuadraticHexahedron to view FEA meshes and results for linear 8-node brick elements and quadratic 20-node brick elements.  I noticed that when using the vtkProperty.SetEdgeVisibility(1) to show the cell edges, the vtkQuadraticHexahedron shows triangles on the cell faces.  The triangle lines on the quadratic cell faces are from a middle edge point across the cell face to the edge points on adjacent face edges, in addition to the edge lines between the corner points.  There is also one straight line across the cell face between two of the middle edge points on opposite edges of the face. The linear vtkHexahedron cell shows only the edge lines between corner points.

I haven't found another option in vtkProperty to change the appearance of the quadratic cell visible edges.  Is there a property, or perhaps a filter that would show only the 12 edge curves between the 8 cell corners and not show the extra triangle lines within the cell face?

If the triangle lines on the cell faces are intrinsic to the vtkQuadraticHexahedron cell, one approach would be to omit the mid side edge points from the data when showing the brick element mesh and just use the vtkHexahedron.  But it would be nice to show curved edges using the mid side point locations if possible.  Or would converting the 3D hex cells to a quadratic quad cells be worthwhile, if that would show just the faces visible on the mesh surfaces?  I've found discussion in vtkusers about adding a second actor to the scene that contains just the edges.  Using two actors: one actor would show the 3D cells and another actor would show just the edges and then superimpose both actors.  I would appreciate your insight to possible changes to my approach to improve the appearance of the quadratic hexahedron edges.

Thank you for your help.

Regards,
Greg Thorwald

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