[vtkusers] about use vtkPolyDataNormals

[Bill Lorensen]

As the documentation says, splitting is used so that "sharp edges can
be split and points duplicated with separate normals to give crisp
(rendered) surface definition."

On Thu, Nov 26, 2009 at 10:38 AM, David Doria <daviddoria+vtk at gmail.com> wrote:
> On Thu, Nov 26, 2009 at 10:04 AM, renlishen <renlishen at gmail.com> wrote:
>>
>> David, thanks~
>> I find the key point to my question...
>> If I don't use the vtkPolyDataNormals' SplittingOff()
>> I get more points and normals like this
>> pic1:
>> http://old.nabble.com/file/p26530678/11.png
>>
>> but when I use SplittingOff()
>> I get the correct number of points and normals
>> pic2:
>> http://old.nabble.com/file/p26530678/22.png
>>
>>
>> but I don't know why vtkPolyDataNormals need to "splitting" the edge.....
>> anyway~thanks again for your replying...^^
>>
>>
>> p.s. my data has 5 points and 6 cell(face)
>> After using SplittingOff() ----> 5 points and 5 normals(pic2)
>> If no use SplittingOff()    ----> 16 points and 16 normals(pic1)
>>
>
> It looks to me like SplittingOff() is finding the average normal at each
> point. You can see this by looking at the tip of your pyramid - the normal
> that exists in 22.png does not exist in 11.png - it is the average of the 4
> vectors. With SplittingOn() - it looks like it is simply using the normal of
> the face. Since each point is connected to multiple faces, there are
> multiple normals.
>
> Hope that helps.
>
> Thanks,
>
> David
>
>
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