[vtkusers] getting a blank volume when trying to perform an x-ray projection in Java

[Mark Roden]

Hi all,

Happy New Year :)

I'm trying to create an average intensity projection through a CT
volume using Java and vtk 5.6.1.  I have the following function in my
panel class, with each vtk object defined as a member object just to
be on the safe side viz garbage collection:

    //the following function will initialize a ray-cast volume to display.
    //the result is stored in the vtkVolume in the class so it can be removed
    //when the display is toggled off.
    vtkVolume mVolumeViewProp = new vtkVolume();;
    vtkVolumeRayCastCompositeFunction rayCastFunction = new
vtkVolumeRayCastCompositeFunction();
    vtkVolumeRayCastMapper rayCastMapper = new vtkVolumeRayCastMapper();
    vtkColorTransferFunction volumeColor = new vtkColorTransferFunction();
    vtkPiecewiseFunction volumeScalarOpacity = new vtkPiecewiseFunction();
    vtkPiecewiseFunction volumeGradientOpacity = new vtkPiecewiseFunction();
    vtkVolumeProperty volumeProperty = new vtkVolumeProperty();
    private void InitializeRayCasting(){
        rayCastMapper.SetInput(imageData);
        rayCastMapper.SetVolumeRayCastFunction(rayCastFunction);

        volumeColor.AddRGBPoint(-1000, 0.0, 0.0, 0.0);
        volumeColor.AddRGBPoint(-400, 1.0, 0.5, 0.3);
        volumeColor.AddRGBPoint(300, 1.0, 0.5, 0.3);
        volumeColor.AddRGBPoint(550, 1.0, 1.0, 0.9);
        volumeScalarOpacity.AddPoint(-1000, 0.00);
        volumeScalarOpacity.AddPoint(-400, 0.15);
        volumeScalarOpacity.AddPoint(300, 0.15);
        volumeScalarOpacity.AddPoint(550, 0.85);
        volumeGradientOpacity.AddPoint(0,   0.0);
        volumeGradientOpacity.AddPoint(90,  0.5);
        volumeGradientOpacity.AddPoint(100, 1.0);
        volumeProperty.SetColor(volumeColor);
        volumeProperty.SetScalarOpacity(volumeScalarOpacity);
        volumeProperty.SetGradientOpacity(volumeGradientOpacity);
        volumeProperty.SetInterpolationTypeToLinear();
        volumeProperty.ShadeOn();
        volumeProperty.SetAmbient(0.4);
        volumeProperty.SetDiffuse(0.6);
        volumeProperty.SetSpecular(0.2);
        mVolumeViewProp.SetMapper(rayCastMapper);
        mVolumeViewProp.SetProperty(volumeProperty);
    }

When the user hits the appropriate button, the following code is run
to initialize the display:

            InitializeRayCasting();
            renWin.GetRenderer().AddViewProp(mVolumeViewProp);
            Render();

Right now, the displayed volume is blank.  What can I do to track this
down?  This code is the medical sample code, but changing the color
and opacity defaults there to something I estimate as being closer to
CT (which ranges in value from -1000 to 3000 in values).  I would
expect something strange looking while I tweak those values, but I
wouldn't expect complete blankness.

There are other objects that get rendered into this same volume
(segmentations of organs)-- will the order of the actors matter when
adding props?

Thanks,
Mark