[vtkusers] vtkExtractEdges changes point IDs?

[Burnie West]

On 04/09/2010 08:00 PM, David Gobbi wrote:
> On Fri, Apr 9, 2010 at 6:41 PM, Burnie West<west at ieee.org>  wrote:
>    
>> The word "usually" troubles me. In what cases might I expect the output
>> points to be ordered differently from the input points for a filter that
>> traverses the points?
>>      
> If you are asking if there is a specific superclass for filters that
> keep the same point ordering, the answer is that there is not.  But
> here is a brief sampling of filters that will guarantee the same
> ordering:
>
> Filters that create/modify cells while keeping all points:
> vtkDelaunay2D, vtkDelaunay3D, vtkTriangleFilter, vtkStripper, vtkReverseSense.
>
> Filters that change point positions without changing cells:
> vtkTransformPolyDataFilter, vtkShrinkPolyData, vtkWarpTo, etc.
>
> Filters that act on point scalars without changing geometry:
> vtkProbeFilter etc.
>
> And here is the exception that proves the rule:  The
> vtkPolyDataNormals filter only provides this guarantee if its
> Splitting option is turned off.
>
> So, hopefully this is about what you would expect.  Note that this
> thread was started with a question about vtkExtractEdges.  Any filter
> that does geometry extraction, clipping, etc. will not maintain
> ordering.
>
>     - David
>    
Very helpful, David.  thank you.