[Paraview] sources: why redundant number of points needed?

[B.W.H. van Beest]

Hi,

When I look into the source code of vtkCubeSource.cpp,
I noticed that, although  a (rectangular) 3D box can be described by
8 3D points and 6 2D faces (hence also 6 3D normal vectors),
in the actual code of vtkCubeBoxSource:RequestData() there are 24 3D
points generated,
with for every point a normal (???), and indeed 6 faces (polys).
Why is there this redundancy?

I bumped on this when I applied the "HiddenLineRemoval" representation to
my own handcrafted box (with 8 points, 6 faces and 6 normals). It yielded
an incorrect view whereas the box with the redundant numbers of data
gave the correct one. But I don't get the logic.

Regards,
Bertwim