[vtkusers] Volume rendering with ray casting

[Madhusudhanan Balasubramanian]

Hi all,
 
I've a volume data that I tried to volume render with ray casting(which I constructed from 5, 2D images).  I've a couple of questions at this time:
 
1. When I rotate the volume around, assuming that image slice 1 is visible, I expect the see the structures in other slices; say if I rotate it 180 degrees around I'm expecting to see structures from image slice 5; but I still see only the structures from slice 1.  Am I missing something while rendering?  (I've verified the dimensions of the volume dataset and it is correct).
 
2. Are there segmentation algorithms that are available with vtk that can used on 2D images before being volume rendered?
 
3. With the volume built from 5 image slices, when I rotate the volume around, the thickness of the volume (along z-axis) appears to be got just from a single image.  May be I'm doing something wrong in rendering.
 
Here are few fragments of my code that I used to volume render:
 
CVolRendererView::CVolRendererView()
{
 this->color = vtkPiecewiseFunction::New();
 this->color->AddPoint(0, 0.0);
 this->color->AddPoint(255, 1.0);
 
 this->opacity = vtkPiecewiseFunction::New();
 this->opacity->AddPoint(0, 0.0);
 this->opacity->AddPoint(130, 0.0);
 this->opacity->AddPoint(140, 1.0);
 this->opacity->AddPoint(255, 1.0);
 
 this->gradOpacity = vtkPiecewiseFunction::New();
 this->gradOpacity->AddPoint(0, 0.0);
 this->gradOpacity->AddPoint(3, 0.0);
 this->gradOpacity->AddPoint(6, 1.0);
 this->gradOpacity->AddPoint(255, 1.0);
 
 this->property = vtkVolumeProperty::New();
 this->property->SetColor(this->color);
 this->property->SetScalarOpacity(this->opacity);
 this->property->SetGradientOpacity(this->gradOpacity);
 this->property->ShadeOn();
 this->property->SetInterpolationTypeToLinear();
 
 this->composite = vtkVolumeRayCastCompositeFunction::New();
 this->composite->SetCompositeMethodToInterpolateFirst();
 
 this->mapper = vtkVolumeRayCastMapper::New();
 this->mapper->SetVolumeRayCastFunction(composite);
 
 this->volume = vtkVolume::New();
 this->volume->SetMapper(this->mapper);
 this->volume->SetProperty(this->property);
 
 this->ren = vtkRenderer::New();
 this->ren->AddVolume(volume);
 this->renWin = vtkWin32OpenGLRenderWindow::New();
 
 this->iren = vtkRenderWindowInteractor::New();

 this->imageAppend = vtkImageAppend::New();
 this->imageAppend->SetAppendAxis(2);
 
 this->renWin->AddRenderer(this->ren);
 this->iren->SetRenderWindow(this->renWin);
 this->iren->Start();
}
 
//Updating the volume with new image slices
this->imageAppend->AddInput(this->GetDocument()->reader->GetOutput());
this->imageAppend->UpdateWholeExtent();

//Rendering
this->mapper->SetInput((vtkImageData*)this->imageAppend->GetOutput());
this->ren->ResetCamera();
this->renWin->Render();

I would appreciate your inputs on this.
 
Thanks,
Madhu.

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