[vtkusers] Fwd: Unsure how to use vtkDelaunay3D

David Gobbi david.gobbi at gmail.com
Mon Jun 1 21:06:39 EDT 2015

That's what the vtkDataSetMapper does when it renders: if it's input is a
3D mesh, then it just renders the surface.  You'd probably need to use
something like vtkExtractEdges to turn it into a space-filling wireframe.

I don't do much mesh work with VTK, so hopefully someone else can chime in
with different ways to render 3D meshes.

 - David

On Mon, Jun 1, 2015 at 7:00 PM, vtk matt <vtkmatt at gmail.com> wrote:

> Yeah this was my understanding.  Any idea then why I only see surface
> triangles when I render it?  I set my actor to wireframe mode and I see no
> internal structure.  Maybe this is just a visualization thing?  With the
> info you provided I did iterate across all cells and cast them to type
> vtkTetra and they all have four faces which is good.  It would be great to
> see this visualized though as a sanity check that I do in fact have
> tetrahedrons.  Thanks again.
> On Mon, Jun 1, 2015 at 5:52 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>> The documentation for vtkDelaunay3D says that it outputs only
>> tetrahedrons unless you specifically set the "Alpha" value (I'm not 100%
>> sure what "Alpha" is for, but since you aren't using it, I don't think you
>> need to worry about it).
>>  - David
>> On Mon, Jun 1, 2015 at 6:19 PM, vtk matt <vtkmatt at gmail.com> wrote:
>>> Hi David,
>>> Thanks for the clarification.  I
>>> ran tets->GetOutput()->GetNumberOfElements(vtkDataObject::CELL) and got a
>>> value of 18 for my input which would make sense as the number of
>>> tetrahedrons.  Do you know if I can expect these cells to in fact contain
>>> tetrahedrons then?
>>> --Matt
>>> On Wed, May 27, 2015 at 8:17 PM, David Gobbi <david.gobbi at gmail.com>
>>> wrote:
>>>> Hi Matt,
>>>> You've been misled by VTK's rather terse documentation:
>>>>   Get the number of elements for a specific attribute type (POINT,
>>>> CELL, etc.).
>>>> For a mesh, you can call GetNumberOfElements(vtkDataObject::POINT) or
>>>> you can call GetNumberOfElements(vtkDataObject::CELL).  Those are the only
>>>> two choices.  You can't ask for a particular type of cell, all you can do
>>>> is ask it to return the total number of cells.
>>>>  - David
>>>> On Wed, May 27, 2015 at 5:41 PM, vtk matt <vtkmatt at gmail.com> wrote:
>>>>> Hi all,
>>>>> I have spent the past few days trying to figure out how to use
>>>>> vtkDelaunay3D properly and decided I'd better seek out some help.  My goal
>>>>> is relatively straight-forward:  Given a set of points in 3D, generate a
>>>>> tetrahedral mesh, and use the results to determine which tetrahedron
>>>>> contains an arbitrary point.
>>>>> In its simplest form I am doing the following:
>>>>> vtkSmartPointer<vtkDelaunay3D> tets =
>>>>> vtkSmartPointer<vtkDelaunay3D>::New();
>>>>> tets->SetInput(points);
>>>>> tets->Update();
>>>>> printf("Number of tets: %d\n",
>>>>> tets->GetOutput()->GetNumberOfElements(VTK_TETRA));
>>>>> The output claims there are zero tetrahedrons.  However if I render an
>>>>> actor from tets->GetOutput(), I am able to visualize a wireframe surface
>>>>> mesh, so I know it's doing something.
>>>>> So I guess my questions are the following:  Why does the output not
>>>>> contain any tetrahedrons?  Why does the mesh only show surface triangles?
>>>>> Ultimately what is the proper way to construct a tetrahedral mesh such that
>>>>> I can query which tetrahedron contains an arbitrary point?
>>>>> Thanks.
>>>>> --Matt
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