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

[David Feng]

I see.  I don't think VTK has any classes that will generate such meshes 
automatically, but I could be wrong.

David

Ali Habib wrote:
> Am so sorry for disturbance but,
>  
> to approximate what I really looking for kindly see the attached photo 
> , and thanks alot for your help.
>  
> Best regards
>
> On Wed, Oct 7, 2009 at 10:35 PM, David Feng <dfeng at cs.unc.edu 
> <mailto:dfeng at cs.unc.edu>> wrote:
>
>     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> <mailto: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>>
>                <mailto: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>>
>                <mailto: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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