[vtkusers] Contouring through constant value areas of dataset
Gerrick Bivins
gbivins at objectreservoir.com
Sat Sep 6 17:15:11 EDT 2008
I was just "digesting" it. In my case, those discontinuous regions are in a
single dataset. By that I mean, it's not separated into it's own block. This
is due to the format of the input data...Anyway, So in my case, I don't have
all cells of the dataset with the same value only groups of cells with the
same value.
If I'm understanding you correctly, the contouring algorithm for cells can
only contour cells that have different values on it's nodes? Is that
correct?
Gerrick.
On 9/6/08 4:08 PM, "Burlen Loring" <burlen.loring at kitware.com> wrote:
> Gerrick, right, it just looked odd to me at first. Did you see my follow
> up post?
>
> http://www.vtk.org/pipermail/vtkusers/2008-September/096843.html
>
> To summarize:
>
> If all nodes of a dataset (or in your case block) have a constant value
> then no contour lines get generated because this configuration of cells
> never results in a contour line intersecting any of the cell's edge's.
> See p 166 and 167 of the vtk text for a better explanation. You'd end up
> with all the cells having the configuration of "Case 15" in fig 6-5
> where no contour line is drawn.
>
> Burlen
>
> Gerrick Bivins wrote:
>> 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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>>
>>
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