[Paraview] ExtractSelection loses selection order

[David E DeMarle]

It was not meant to be preserved. For performance reasons the
extraction filter (vtkExtractSelectedIds specifically) sorts both the
selection list and the element id array so that it can do a quick
lookup of the usually numerous entries in the selection list.

David E DeMarle
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x109



On Tue, Jan 19, 2010 at 1:37 PM, David Doria <daviddoria at gmail.com> wrote:
> On Mon, Jan 18, 2010 at 12:31 PM, David Doria <daviddoria at gmail.com> wrote:
>>
>> If I select 3 points and then use the ExtractSelection filter, I would
>> expect the IDs of the points to be 0,1,2, in the order selected.
>> Instead, they are 2, 0, 1.
>>
>> Is there any way to prevent this? I am trying to set corresponding
>> landmarks, so the order is important, and it is being lost.
>>
>> Thanks,
>>
>> David
>
> Here is a demo of the problem:
>
> http://www.rpi.edu/~doriad/Paraview_List/ExtractSelection/
>
> points.vtp contains 10 points, (0-9). I selected points 9, 8, 7, in that
> order and extracted the selection. The result (extracted.vtp) has the 3
> extracted points (corresponding to 9,8,7) ordered 2, 1, 0, rather than 0, 1,
> 2, which was the selection order.
>
> Is this a bug or was the ordered never intended to be preserved?
>
> Thanks,
>
> David
>
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