[vtk-developers] vtkUnstructuredGrid - Not rendering Overlapping Cells

Fri Feb 22 12:27:59 EST 2013

You guessed it right. I do use a vtkDataSetMapper.

But I am puzzled because I do the exact same thing for a VTKStructuredGrid
- create grid, use threshold filter then a vtkDataSetMapper. In that case
all faces are extracted and rendered.

Maybe vtkDataSetMapper acts differently depending on what its input is?
That is if its input came from a structured grid, render all.

But then again, in my code, vtkDataSetMapper sees the threshold output not
directly the grid.

On Fri, Feb 22, 2013 at 11:13 AM, Will Schroeder <will.schroeder at kitware.com
> wrote:

> I'm guessing that you are using a vtkDataSetMapper (or equivalent) which
> under the hood uses some sort of geometry filter.
>
> When you use different nodes, the boundary operations return the number of
> uses of a face as being <=1 hence a boundary face, and hence rendered. With
> the same nodes, each face is used twice hence is an interior face and not
> extracted, and hence nothing is rendered.
>
> W
>
>
> On Fri, Feb 22, 2013 at 12:03 PM, Bhanu Hariharan <bhanu at petrotel.com>wrote:
>
>> 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
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>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>> _______________________________________________
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>>>
>>>
>>> --
>>> William J. Schroeder, PhD
>>> Kitware, Inc.
>>> 28 Corporate Drive
>>> Clifton Park, NY 12065
>>> will.schroeder at kitware.com
>>> http://www.kitware.com
>>> (518) 881-4902
>>>
>>
>>
>
>
> --
> William J. Schroeder, PhD
> Kitware, Inc.
> 28 Corporate Drive
> Clifton Park, NY 12065
> will.schroeder at kitware.com
> http://www.kitware.com
> (518) 881-4902
>
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