[vtkusers] unstructured grid + tetrahedrons

[Cory Quammen]

Isn't a lot of this information already in the following file:

http://www.vtk.org/VTK/img/file-formats.pdf

Cory

On Mon, Dec 14, 2009 at 5:01 PM, David Doria <daviddoria+vtk at gmail.com> wrote:
> 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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>
> 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
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-- 
Cory Quammen
Center for Computer Integrated Systems for Microscopy and Manipulation (CISMM)
Department of Computer Science
University of North Carolina at Chapel Hill
http://www.cs.unc.edu/~cquammen