[vtk-developers] Fwd: vtkUnstructuredGridVolumeRayCastMapper (05B22CB8): Can't use the ray cast mapper without scalars!

David Feng dfeng at cs.unc.edu
Wed Oct 7 16:35:39 EDT 2009


If you look at the edges, you'll see that it is actually made of up 
triangles:

actor.SetRepresentationToWireframe()

There are other ways of approximating spheres with geometry, but it 
doesn't look like they are in VTK. 

David

Ali Habib wrote:
> thanks alot for your great efforts,
>  
> Please I have another question it's not a perfect traingle ,I want to 
> create a mesh to be used in FEM any advice please
>  
>  
> best regards
>
> On Wed, Oct 7, 2009 at 9:59 PM, David Feng <dfeng at cs.unc.edu 
> <mailto:dfeng at cs.unc.edu>> wrote:
>
>     I haven't used the vtkUnstructuredGridVolumeRayCastMapper before,
>     nor do I know anything about meshing.   I'm guessing that
>     vtkUnstructuredGridVolumeRayCastMapper is trying to composite all
>     of the scalars on the geometry points, and fails when there aren't
>     any.
>     It looks like you're trying to set the scalars with this code:
>
>     unstructuredReader->GetOutput()->GetPointData()->AddArray(arr);
>     unstructuredReader->GetOutput()->GetPointData()->SetActiveScalars("myarray");
>
>     I'd be careful with that.  Modifications to the output of a filter
>     often get wiped out when the filter updates.  Better to make a
>     copy of the output, if you have space:
>
>     copy = vtkUnstructuredGrid::New()
>     copy->DeepCopy(unstructuredReader->GetOutput());
>     copy->GetPointData()->SetScalars(arr);
>
>     But it seems like you really don't care about scalars defined at
>     points, since you're just filling the scalar array with 1.0
>     everywhere.  If all you want is to see a surface, then render it
>     using one of the standard geometry mappers.  The code would look
>     something like this, in python:
>
>     -----------
>     sphereSource = vtk.vtkSphereSource()
>     delaunay = vtk.vtkDelaunay3D()
>     delaunay.SetInputConnection(sphereSource.GetOutputPort())
>
>     mapper = vtk.vtkDataSetMapper()
>     mapper.SetInputConnection(delaunay.GetOutputPort())
>
>     actor = vtk.vtkActor()
>     actor.SetMapper(mapper)
>
>     ren = vtk.vtkRenderer()
>     rwin = vtk.vtkRenderWindow()
>     iren = vtk.vtkRenderWindowInteractor()
>
>     ren.AddActor(actor)
>     rwin.AddRenderer(ren)
>     rwin.SetInteractor(iren)
>     iren.Start()
>     -------------
>
>     I tested this out and it rendered a sphere.  It looks the same as
>     the normal output from vtkSphereSource.  Again, I'm not familiar
>     with what you're trying to do, but hopefully this was helpful.
>
>     David
>
>     Ali Habib wrote:
>
>         Dear All
>          I know it's for developing just , but I sent 6 times to vtk
>         user forum , with no reply helped me , so I am not sure is
>         this bug or not
>          best regards
>
>         ---------- Forwarded message ----------
>         From: *Ali Habib* <ali.mahmoud.habib at gmail.com
>         <mailto:ali.mahmoud.habib at gmail.com>
>         <mailto:ali.mahmoud.habib at gmail.com
>         <mailto:ali.mahmoud.habib at gmail.com>>>
>         Date: Tue, Sep 29, 2009 at 9:47 PM
>         Subject: vtkUnstructuredGridVolumeRayCastMapper (05B22CB8):
>         Can't use the ray cast mapper without scalars!
>         To: vtkusers at vtk.org <mailto:vtkusers at vtk.org>
>         <mailto:vtkusers at vtk.org <mailto:vtkusers at vtk.org>>
>
>
>         I wrote a code to make tetrahedral mesh on sphere , but it no
>         give result except :
>          ERROR: In
>         m:\dev\cur\vtkdotnet\branch\50\VolumeRendering\vtkUnstructuredGridVolumeRayCastMapper.cxx,
>         line 274
>         vtkUnstructuredGridVolumeRayCastMapper (05B22CB8): Can't use
>         the ray cast mapper without scalars!
>          every time I  run the code
>          attached is the c++ code , your fast reply is highly appretiated
>           best regards
>
>         ------------------------------------------------------------------------
>
>
>
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