[vtkusers] unstructured grid + tetrahedrons

[David Doria]

On Fri, Dec 11, 2009 at 2:41 PM, Dominik Szczerba <dominik at itis.ethz.ch> wrote:
> Baliki B. wrote:
>>
>> I tried vtkShrinkFilter and it worked.  My question is why using
>> vtkShrinkFilter and pressing w key shows tetrahedrons and without it(e.g.
>> using the original unstructured grid) doesn't? Is it something with the fact
>> you say it results in "polydata" ?
>
> AFAIR 'w' is a shortcut for wireframe representation.
>
>>
>> Why you give emphasis in "results in polydata" in both first two methods
>> (vtkShrinkFilter and vtkExtractGeometry) ? Is something "wrong" the polydata
>> we get?
>
> Nothing wrong, just what you get is formally a polydata. You do not see your
> tets, at least not directly: you see them as their faces.
>
>>
>> Also, i read in the book that polydata is types(vertices, lines, polygons
>> and triangle strips) which is limited and that's why we use unstructured
>> grid to represent a tetrahedron.
>> Am i missing something?
>
> See above. How would you actually like to see your tet? If you just want to
> see its faces, shrink or extract geometry filter is enough, even if
> producing polygons (tet's faces/triangles)
>
> Dominik
>
>>
>> 2009/12/10 Dominik Szczerba <dominik at itis.ethz.ch
>> <mailto:dominik at itis.ethz.ch>>
>>
>>    Unfortunately, I will not have a possibility to write those examples
>>    this time. A few quick comments follow below.
>>
>>
>>    David Doria wrote:
>>
>>        On Thu, Dec 10, 2009 at 8:52 AM, Baliki B. <balikivtk at gmail.com
>>        <mailto:balikivtk at gmail.com>> wrote:
>>
>>            Could you explain (with some code) a little bit more?
>>
>>
>>            2009/12/10 Dominik Szczerba <dominik at itis.ethz.ch
>>            <mailto:dominik at itis.ethz.ch>>
>>
>>                You can see your tets in multiple ways:
>>
>>                - extract cells by region
>>
>>
>>    There is a filter (vtkExtractGeometry) to extract parts of a volume
>>    mesh NOT cutting the cells. Resulting is a polydata of course, but
>>    you see the inside cells otherwise hidden. Combined with an
>>    interactive widget (e.g. vtkBoxWidget) and edge visibility it gives
>>    a very good view.
>>
>>                - cell shrinking
>>
>>
>>    You can shrink all the cells by a factor (vtkShrinkFilter). This
>>    will result in a polydata again, but you will see the separate cells
>>    (by their 4 shrinked triangles).
>>
>>
>>
>>                To see the associated data:
>>                - volume rendering
>>
>>
>>    see vtkVolume
>>
>>                - cut slices
>>
>>
>>    see vtkCutter
>>
>>                - clip
>>
>>
>>    see vtkClipDataSet
>>
>>                - contouring
>>
>>
>>    see vtkContourFilter
>>
>>    Dominik
>>
>>
>>
>>                Dominik
>>
>>
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>>
>>
>>        It's sounding like this may call for a couple of examples...
>>
>>        Thanks,
>>
>>        Captain Example
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>>    Powered by www.kitware.com <http://www.kitware.com>
>>
>>    Visit other Kitware open-source projects at
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>>
>>    Please keep messages on-topic and check the VTK FAQ at:
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All,

I started a little page to help us not get confused about the data
types and to point new users to when they are confused.

http://www.cmake.org/Wiki/VTK_3D_Data_Types

Anyone care to add anything?

Thanks,

David