[vtkusers] Contouring through constant value areas of dataset

[Gerrick Bivins]

The dataset is a mutliblock dataset with discontinuous scalars. I've used
the solution mentioned in a previous post to accomplish this( using
vtkShrinkFilter with value of 1.0 to explode the dataset and duplicate point
info).
However, I've also run across this issue with a dataset that has continuous
regions. 
As David mentioned below, this issue can be reproduced using any source with
a constant scalar data array assigned to it.
Gerrick

On 9/6/08 10:46 AM, "Burlen Loring" <burlen.loring at kitware.com> wrote:

> Gerrick,
> 
> There is something suspect with the data you are contouring.
> http://www.nabble.com/file/p19338704/constantValues-surface.png
> 
> Let me explain why I think this. Contouring uses interpolation along
> cell edges, making use of nodal data. In my experience, when rendering
> nodal data vtk interpolates so that in the rendered image you never see
> a discontinuity across adjacent cells when adjacent cells share nodes
> (it will always show as a steep but smooth transition). In your images
> we can see discontinuities between the regions, therefor I wonder if
> those cells are actually sharing nodes with their neighbors. ? In other
> words to vtk they might not be connected regions.
> 
> Just a guess.
> Of course it would be easier to help if you posted your data.
> 
> Burlen
> 
> David E DeMarle wrote:
>> Ah, so presumably one of those isocontours happens to hit the
>> contoured value exactly and you expect the whole thing to be drawn but
>> it is not.
>> 
>> You can reproduce the behavior with any Source, using Calculator to
>> give every point the same constant scalar value, and then contouring
>> on that value.
>> 
>> You would expect everything to be drawn, but nothing is. I don't know
>> why it does that.
>> 
>> anyone?
>> 
>> On Fri, Sep 5, 2008 at 4:38 PM, Gerrick Bivins
>> <gbivins at objectreservoir.com> wrote:
>>   
>>> Right. But for instance, if I were visualizing this data via volume
>>> rendering, the areas with this constant value would be displayed rather than
>>> not.
>>> Am I misunderstanding the intent of contouring? If so, is there another
>>> filter I can use to accomplish what I'm describing?
>>> Gerrick
>>> 
>>> 
>>> On 9/5/08 3:29 PM, "David E DeMarle" <dave.demarle at kitware.com> wrote:
>>> 
>>>     
>>>> Umm, because the values are constant? Which means they contain only
>>>> one value, and thus either nowhere contain the value that a contour
>>>> displays, or everywhere contain it.
>>>> 
>>>> I am not sure I understand your question otherwise.
>>>> 
>>>> 
>>>> On Fri, Sep 5, 2008 at 4:17 PM, Gerrick Bivins
>>>> <gbivins at objectreservoir.com> wrote:
>>>>       
>>>>> Hi All,
>>>>> When generating contour values (isosurfaces) with vtkContourFilter, I've
>>>>> noticed that areas in the dataset with constant values ( probably not the
>>>>> correct terminology here) don't produce contours.
>>>>> 
>>>>> For example, here is the original multiblock dataset in Paraview with
>>>>> areas
>>>>> of constant value:
>>>>> http://www.nabble.com/file/p19338704/constantValues-surface.png
>>>>> 
>>>>> Here is the contouring with about 100 values:
>>>>> http://www.nabble.com/file/p19338704/constantValues-100-contours.png
>>>>> 
>>>>> Here is the contouring with ALOT of values:
>>>>> http://www.nabble.com/file/p19338704/constantValues-many-contours.png
>>>>> 
>>>>> Can someone explain why the square area(bottom left of the elliptical
>>>>> dataset) and triangle area (bottom right) don't produce any contours? The
>>>>> only similarities are that the values in those areas are constant in those
>>>>> areas.
>>>>> Gerrick
>>>>> 
>>>>> 
>>>>> --
>>>>> View this message in context:
>>>>> http://www.nabble.com/Contouring-through-constant-value-areas-of-dataset-t
>>>>> p19
>>>>> 338704p19338704.html
>>>>> Sent from the VTK - Users mailing list archive at Nabble.com.
>>>>> 
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>>>     
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