[vtkusers] How to insert edges?

[Sean McInerney]

Oh yeah, sure Jeff ... always taking the easy way out ;-)

vtkTriangleFilter is probably the best solution.

-Sean

Jeff Lee wrote:
> Hi All,
> Would not a vtkTriangleFilter be appropriate in this case?  It does all 
> the accounting for you...
> -J
> 
> Sean McInerney wrote:
> 
>> Hi Petru,
>>
>>   The VTK readers that I am familiar with make no checks WRT the 
>> planarity of quads or polygons ... or convexity for that matter. If 
>> you have degenerate data, then there may be some cleaning up to do.
>>
>>   To break a given quad into two triangles, you will have to remove 
>> the cell entry for the quad as well as inserting the two cell entries 
>> for the triangles. Be careful which methods you use to insert; some 
>> will allocate additional memory while others assume a preallocated 
>> list size and make no checks.
>>
>>   I am not sure that this fully addresses your woes, but hopefully 
>> it's  a good start.
>>
>> -Sean
>>
>> Petru Pau wrote:
>>
>>> After weeks of failures and bad results, I have discovered the reason:
>>> in the huge vtkPolyData that I read as input, some quads do not have
>>> coplanar vertrices. (Side question: Can it be that vtk avoids making 
>>> planarity
>>> tests for quads and polygons?)
>>>
>>> The most immediate solution is to insert a few new edges: the 
>>> diagonals of
>>> these quads.
>>>
>>> I tried to do that and failed. First, simply inserting next cell does 
>>> not work,
>>> if the list of lines of the poly data is null. Second, if I take the 
>>> lines of
>>> the poly data, add the new edge to it, and set it back as the lines 
>>> of the
>>> poly data, the process fails in the subsequent BuildLinks.
>>>
>>> The question is now evident: How can I insert and edge in a vtkPolyData?
>>>
>>> Petru
>>>
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>