[Paraview] Disappearing volume rendering?

[Burlen Loring]

do you have any scalars? those are not optional for volume rendering. 
Additionally you may need to adjust the transfer function,

On 10/13/2014 10:22 AM, B.W.H. van Beest wrote:
> No, it doesn't work. The filter creates tets, which are visible in the
> wireframe representation,
> but when I select "Volume"  representation the image disappears.
>
> I can't imagine it is so difficult to render a volume in Paraview. I
> must be doing something wrong....
>
> Regards,
> Bertwim
>
> On 10/13/2014 05:36 PM, Cory Quammen wrote:
>> Bertwim,
>>
>> I'm not sure that the volume renderer can handle VTK_HEXAHEDRON
>> elements. Try the "Tetrahedralize" filter on your source and see if
>> the Volume representation works.
>>
>> Thanks,
>> Cory
>>
>> On Mon, Oct 13, 2014 at 10:19 AM, B.W.H. van Beest <bwvb at xs4all.nl> wrote:
>>> Hi,
>>>
>>> I'm struggling to get a proper 3D view of my model system (yes,
>>> embarrassing!)
>>> but must admit my defeat.
>>> After stripping almost everything, keeping the minimum to exhibit the
>>> issue,
>>> I'm left with the following:
>>>
>>> I have created a simple box source. To get a 3D representation, I
>>> sub-classed
>>> the code for this Source from vtkUnstructuredGridAlgorithm.
>>>
>>> In the RequestData method, I define the 8 point of the unit cube. I
>>> added the points to the
>>> underlying unstructed grid, and I specified the cell topology.
>>>
>>> This all seems to work: when instantiating this box Source, I *do* get the
>>> expected cube in the representations (Surface, wireframe, Points).
>>>
>>> However, when I select the "Volume" representation, *the image disappears*
>>> What am I doing wrong?
>>>
>>> As the code is not too long and very simple, I take the freedom to paste
>>> it below.
>>>
>>> Kind regards.
>>> Bertwim
>>>
>>> =========================================
>>>
>>>   int sphBoxSourceC::RequestData( vtkInformation *vtkNotUsed(request),
>>>                                  vtkInformationVector
>>> **vtkNotUsed(inputVector),
>>>                                  vtkInformationVector *outputVector)
>>> {
>>>     // Get the info object
>>>     vtkInformation *outInfo = outputVector->GetInformationObject(0);
>>>     vtkUnstructuredGrid *umesh = vtkUnstructuredGrid::SafeDownCast(
>>> outInfo->Get( vtkDataObject::DATA_OBJECT() ) );
>>>
>>>     // Pre-allocate some memory
>>>     umesh->Allocate( 1024 );
>>>
>>>     // Specify points.
>>>     double r0[] = { 0.0, 0.0, 0.0 };
>>>     double r1[] = { 1.0, 0.0, 0.0 };
>>>     double r2[] = { 0.0, 1.0, 0.0 };
>>>     double r3[] = { 1.0, 1.0, 0.0 };
>>>     double r4[] = { 0.0, 0.0, 1.0 };
>>>     double r5[] = { 1.0, 0.0, 1.0 };
>>>     double r6[] = { 0.0, 1.0, 1.0 };
>>>     double r7[] = { 1.0, 1.0, 1.0 };
>>>
>>>     // Collect the points in a vtk data structures.
>>>     {
>>>        vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
>>>        points->SetDataType( VTK_DOUBLE );
>>>
>>>        points->InsertNextPoint( r0 );
>>>        points->InsertNextPoint( r1 );
>>>        points->InsertNextPoint( r2 );
>>>        points->InsertNextPoint( r3 );
>>>        points->InsertNextPoint( r4 );
>>>        points->InsertNextPoint( r5 );
>>>        points->InsertNextPoint( r6 );
>>>        points->InsertNextPoint( r7 );
>>>
>>>        // Transfer points to umesh.
>>>        umesh->SetPoints( points );
>>>     }
>>>
>>>     // Cell Topology
>>>     vtkIdType vtx[8] = { 0, 1, 3, 2, 4, 5, 7, 6 };
>>>     umesh->InsertNextCell( VTK_HEXAHEDRON, 8, vtx );
>>>
>>>     return 1;
>>> }
>>>
>>>
>>>
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