[vtk-developers] vtkUnstructuredGrid - Not rendering Overlapping Cells

Fri Feb 22 12:03:47 EST 2013

Thanks Will.
You are right. In my application,  I do use a filter BUT that is a
VTKThreshold filter for showing only certain cells.
If the two overlapping cells pass this threshold filter, then I don't see
them at all (if i use structured grid, then you are right I see something
not pretty but I see something).

I did not use a VTKDataSetSurface filter. I understand if I used that then
only the boundary cells will be rendered.
But what I used was just a threshold filter.

Infact I created a small ascii file with 2 cells and opened in Paraview as
a Legacy VTK file.
No filter. I cant see the two cells if ALL NODES ARE IDENTICAL.

But if some nodes are identical and some different, then I see some
surfaces.

Both cases copied here.

//===============ALL NODES IDENTICAL=================NOTHING RENDERED
# vtk DataFile Version 3.0
vtk output
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 8 float
0 0 0
1 0 0
1 1 0
0 1 0
0 0 1
1 0 1
1 1 1
0 1 1
CELLS 2 18
8 0 1 3 2 4 5 7 6
8 0 1 3 2 4 5 7 6
CELL_TYPES 2
12
12

//===============SOME NODES IDENTICAL=================SOME FACES RENDERED
# vtk DataFile Version 3.0
vtk output
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 10 float
0 0 0
1 0 0
0 1 0
1 1 0
0 0 1
1 0 1
0 1 1
1 1 1
1 1 0
1 1 1
CELLS 2 18
8 0 1 3 2 4 5 7 6
8 0 1 8 2 4 5 9 6
CELL_TYPES 2
12
12

Thanks
Bhanu

On Fri, Feb 22, 2013 at 10:40 AM, Will Schroeder <will.schroeder at kitware.com
> wrote:

> Rendering is not the problem. You can render a zillion things on top of
> each other. It won't look pretty but you'll see something.
>
> Probably what is the problem is that you are going through some sort of
> geometry filter. For 3D cells, the geometry filter looks at the number of
> times each "face" is used by 3D cells. It the number of uses is <=1, then
> it's a boundary face and is rendered. If used 2 times, then it's an
> interior cell and not extracted (nor rendered).
>
> W
>
>
> On Fri, Feb 22, 2013 at 10:56 AM, Bhanu Hariharan <bhanu at petrotel.com>wrote:
>
>> Thanks. I will look into the composite dataset but I do not have anything
>> other than hexahedrons.
>>
>> I think it looks like VTKUnstructuredGrid will not render in the
>> situation of overlapping cells and I have to find a way out outside of VTK.
>>
>>
>>
>>
>> On Fri, Feb 22, 2013 at 9:28 AM, Sebastien Jourdain <
>> sebastien.jourdain at kitware.com> wrote:
>>
>>> VTK has other type of data structure such a composite-dataset /
>>> multi-block which let you create a dataset that is composed of multiple
>>> dataset (i.e. Unstructured grid in your case).
>>> And what you do is basically share the same vtkPoints across all your
>>> unstructured grids which will then be gathered by the composite dataset.
>>> and rendered as a single dataset.
>>>
>>> Hope that explain a bit more,
>>>
>>> Seb
>>>
>>>
>>> On Fri, Feb 22, 2013 at 10:24 AM, Bhanu Hariharan <bhanu at petrotel.com>wrote:
>>>
>>>> Sebastian, I do not understand what you mean by multi-block. Could you
>>>> please elaborate. Thanks.
>>>>
>>>>
>>>> On Fri, Feb 22, 2013 at 9:20 AM, Sebastien Jourdain <
>>>> sebastien.jourdain at kitware.com> wrote:
>>>>
>>>>> Unless it's a multi-block and then it is not the same dataset
>>>>> anymore...
>>>>>
>>>>>
>>>>> On Fri, Feb 22, 2013 at 10:17 AM, Sebastien Jourdain <
>>>>> sebastien.jourdain at kitware.com> wrote:
>>>>>
>>>>>> Then I'm not sure that VTK can handle 2 cells that are based on
>>>>>> exactly the same points ID.
>>>>>>
>>>>>>
>>>>>> On Fri, Feb 22, 2013 at 10:12 AM, Bhanu Hariharan <bhanu at petrotel.com
>>>>>> > wrote:
>>>>>>
>>>>>>> Thanks Sebastian. For the 2 cell case, I start with 16 points and
>>>>>>> identify duplicates and bring it down to 8 and the two cells now map to the
>>>>>>> same 8 nodes. In this scenario, can VTK render both cells with some flags
>>>>>>> turned on.
>>>>>>> Or can you please suggest another way.
>>>>>>>
>>>>>>> But removing duplicate nodes is a must for my application due to
>>>>>>> memory constraints.
>>>>>>>
>>>>>>> -Bhanu
>>>>>>>
>>>>>>>
>>>>>>> On Fri, Feb 22, 2013 at 9:03 AM, Sebastien Jourdain <
>>>>>>> sebastien.jourdain at kitware.com> wrote:
>>>>>>>
>>>>>>>> duplicate the points.
>>>>>>>>
>>>>>>>>
>>>>>>>> On Fri, Feb 22, 2013 at 9:59 AM, bhanu <bhanu at petrotel.com> wrote:
>>>>>>>>
>>>>>>>>> Please can anyone answer this query - is this forum active?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> View this message in context:
>>>>>>>>> http://vtk.1045678.n5.nabble.com/vtkUnstructuredGrid-Not-rendering-Overlapping-Cells-tp5718739p5718763.html
>>>>>>>>> Sent from the VTK - Dev mailing list archive at Nabble.com.
>>>>>>>>> _______________________________________________
>>>>>>>>> Powered by www.kitware.com
>>>>>>>>>
>>>>>>>>> Visit other Kitware open-source projects at
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>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
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>
>
> --
> William J. Schroeder, PhD
> Kitware, Inc.
> 28 Corporate Drive
> Clifton Park, NY 12065
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