[vtk-developers] Rationale for vtkWedge point order

[Berk Geveci]

I believe that we had to fix the EnSight reader to deal with this. Is that
right Zhanping?

On Wed, Feb 24, 2010 at 10:08 AM, Mark Olesen <Mark.Olesen at faurecia.com>wrote:

> I ran into this (again).
>
> For the majority of the primitive 3d cell shapes (vtkTetra, vtkPyramid,
> vtkHexahedron, vtkHexagonalPrism, vtkPentagonalPrism), the base forms a
> face whose normal points in the direction of the next face (or point, in
> the case of vtkTetra).
>
> But vtkWedge is defined the opposite way around - the face normals point
> in opposite directions!!
>
> This is presumably historical and probably couldn't be changed without
> breaking a huge amount of code, but what is the rationale for it?
>
> Or is actually immaterial if the specified node order results in cells
> with a negative volume?
>
> The reason for my question is not only that I stumbled on this again,
> but also that other VTK readers seem to be using vtkWedge while assuming
> a different point order.
>
> For example, according to the EnSight documents, their "penta6" is
> defined with a base (0,1,2) that points towards the opposite face
> (3,4,5). The rest of the EnSight shapes are consistent with the node
> order used by VTK. Doesn't this cause inverted cells?
>
>
> /mark
>
>
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