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

[David Feng]

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>>
> 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>
>
>
> 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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