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

[Bill Lorensen]

When you set EdgeVisibility you will see the edges of the triangles
that render the cell. To see the true edges of the cell use the
vtkExtractEdges filter. There is a python test:
/Filters/Extraction/Testing/Python/ExtractEdgesQuadraticCells.py that
illustrates the usage.


On Wed, Sep 11, 2013 at 2:11 PM, Greg Thorwald
<G.Thorwald at questintegrity.com> wrote:
> 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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