[vtkusers] slice structured grid with polydata

[Cory Quammen]

I don't think there are options in VTK that will do what you want,
unfortunately. You would need to manually identify which hexahedra are not
cut and then create a new vtkUnstructuredGrid with those hexahedra as well
as the cut tetrahedra.

On Thu, Mar 24, 2016 at 2:21 PM, Justin Weber <onlyjus at gmail.com> wrote:

> It would be nice if the grid was not tetrahedralized first. I would like
> the original hexahedrons that are not sliced to be preserved.
>
> On Thu, Mar 24, 2016 at 11:59 AM, Cory Quammen <cory.quammen at kitware.com>
> wrote:
>
>> What do you want as output instead?
>>
>> On Thu, Mar 24, 2016 at 10:53 AM, Justin Weber <onlyjus at gmail.com> wrote:
>> > I didn't realize this earlier but the vtkClipDataSet tetrahedralizes the
>> > mesh before slicing? It seems that this is required for the algorithm.
>> Do
>> > you know of any ways to prevent this?
>> >
>> > BTW, here is the link to the example:
>> >
>> http://www.vtk.org/Wiki/VTK/Examples/Python/Meshes/vtkClipDataSetWithPolydata
>> >
>> > Justin
>> >
>> > On Mon, Mar 7, 2016 at 5:30 PM, Cory Quammen <cory.quammen at kitware.com>
>> > wrote:
>> >>
>> >> That's great, Justin. Thanks for reporting back.
>> >>
>> >> Cory
>> >>
>> >> On Mon, Mar 7, 2016 at 4:04 PM, Justin Weber <onlyjus at gmail.com>
>> wrote:
>> >>>
>> >>> Cory,
>> >>>
>> >>> Thanks for your help. I got it working! I might put the code up as an
>> >>> example.
>> >>>
>> >>>
>> >>> Justin
>> >>>
>> >>> On Thu, Feb 18, 2016 at 10:58 PM, Cory Quammen <
>> cory.quammen at kitware.com>
>> >>> wrote:
>> >>>>
>> >>>> Justin,
>> >>>>
>> >>>> There is nothing canned in VTK to do this, but with some work you
>> should
>> >>>> be able to get there using an implicit function created from your
>> STL file.
>> >>>> At a high level, what you would do is create an instance of
>> >>>> vtkImplicitPolyDataDistance. Set its input to the poly data from the
>> STL
>> >>>> file. Then, create a new point data array in your structured grid
>> that
>> >>>> stores the value from the implicit poly data distance filter.
>> Negative
>> >>>> values will be inside the poly data, positive values outside, and 0
>> at the
>> >>>> surface. Finally, use vtkClipDataSet to clip the structured grid a
>> function
>> >>>> value 0. This should give you back an unstructured grid in
>> approximately the
>> >>>> shape of your input STL. It won't be exact because of the
>> interpolation used
>> >>>> by vtkClipDataSet, but it should be close.
>> >>>>
>> >>>> Hope that helps.
>> >>>>
>> >>>> Cory
>> >>>>
>> >>>> On Thu, Feb 18, 2016 at 10:08 PM, Justin Weber <onlyjus at gmail.com>
>> >>>> wrote:
>> >>>>>
>> >>>>> I would like to generate a "cutcell" mesh using vtk by slicing a
>> >>>>> structured grid with polydata loaded from a STL file. The resulting
>> mesh
>> >>>>> would be an unstructured grid.
>> >>>>>
>> >>>>> Are there any tools in vtk to accomplish this?
>> >>>>>
>> >>>>> I can create the structured grid and polydata successfully. Now I
>> just
>> >>>>> need an algorithm to slice the structured mesh with the polydata
>> surface.
>> >>>>>
>> >>>>> In my searching I could not find anything. However, I could
>> accomplish
>> >>>>> this by ray casting to find the intersections between the
>> structured grid
>> >>>>> and the polydata. Then using those points to create the
>> unstructured grid.
>> >>>>>
>> >>>>> See attached 2d sketch.
>> >>>>>
>> >>>>> Thanks!
>> >>>>> Justin
>> >>>>>
>> >>>>>
>> >>>>> _______________________________________________
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>> >>>>>
>> >>>>> Please keep messages on-topic and check the VTK FAQ at:
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>> >>>>>
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>> >>>>>
>> >>>>
>> >>>>
>> >>>>
>> >>>> --
>> >>>> Cory Quammen
>> >>>> R&D Engineer
>> >>>> Kitware, Inc.
>> >>>
>> >>>
>> >>
>> >>
>> >>
>> >> --
>> >> Cory Quammen
>> >> R&D Engineer
>> >> Kitware, Inc.
>> >
>> >
>>
>>
>>
>> --
>> Cory Quammen
>> R&D Engineer
>> Kitware, Inc.
>>
>
>


-- 
Cory Quammen
R&D Engineer
Kitware, Inc.
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