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

[B.W.H. van Beest]

Cory,

So indeed there has to be a normal *per point and per face*, and not
*per face*?
And, likewise, points are not shared between adjacent faces.
I had overlooked that detail in the documentation, tacitly assuming that
"of course"
the normals are  *per face*.

Regards,
Bertwim

On 10/11/2014 04:48 PM, Cory Quammen wrote:
> Bertwim,
>
> You are right that there is a redundancy in points. That stems from
> the need for defining different normals at the corner points for each
> face. In theory, you could define more than one normal for the same
> point and associate it with a face, but that complicates the data
> structure. It is much simpler to duplicate points and associate
> exactly one normal per point.
>
> In most polygonal data, you won't see duplicated points at most
> places. But for anything that should be displayed with a sharp edge,
> duplicate points will be present.
>
> - Cory
>
> On Sat, Oct 11, 2014 at 10:23 AM, B.W.H. van Beest <bwvb at xs4all.nl> wrote:
>> 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
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