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

[Mark Roden]

I will answer my own question.

The vtkVolumeRayCastMapper requires that the data be unsigned short or
unsigned char.  CT data is short, so the following code will work:

   //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.
    //set these all as new and then null them all in the dispose method,
    //to ensure that they are around as long as necessary but
    //also that they are cleaned up properly.
   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();
   vtkImageData theRecastData = new vtkImageData();
   private void InitializeRayCasting(){
       vtkImageShiftScale theShifter = new vtkImageShiftScale();
       theShifter.SetShift(2000);//in case there are values less than
-1000, just
       //add 2000 to all volumes and scale accordingly, assuming that
       //0 (now 2000) should be properly calibrated for water in HUs.
       theShifter.SetOutputScalarTypeToUnsignedShort();
       theShifter.SetInput(imageData);
       theShifter.Update();
       vtkImageData theOutput = theShifter.GetOutput();
       theRecastData.DeepCopy(theOutput);

       rayCastMapper.SetInput(theRecastData);
       rayCastMapper.SetVolumeRayCastFunction(rayCastFunction);

       volumeColor.AddRGBPoint(1000, 0.0, 0.0, 0.0);
       volumeColor.AddRGBPoint(1400, 1.0, 0.5, 0.3);
       volumeColor.AddRGBPoint(1800, 1.0, 0.5, 0.3);
       volumeColor.AddRGBPoint(2150, 1.0, 1.0, 0.9);
       volumeScalarOpacity.AddPoint(1000, 0.00);
       volumeScalarOpacity.AddPoint(1400, 0.05);
       volumeScalarOpacity.AddPoint(1800, 0.05);
       volumeScalarOpacity.AddPoint(2150, 0.25);//don't want it to be
too opaque,
       //then it's impossible to see internal organs
       volumeGradientOpacity.AddPoint(0,   0.0);
       volumeGradientOpacity.AddPoint(90,  0.5);
       volumeGradientOpacity.AddPoint(100, 0.25);
       volumeProperty.SetColor(volumeColor);
       volumeProperty.SetScalarOpacity(volumeScalarOpacity);
       volumeProperty.SetGradientOpacity(volumeGradientOpacity);
       volumeProperty.SetInterpolationTypeToLinear();
       volumeProperty.ShadeOn();
       volumeProperty.SetAmbient(0.1);
       volumeProperty.SetDiffuse(0.9);
       volumeProperty.SetSpecular(0.2);
       mVolumeViewProp.SetMapper(rayCastMapper);
       mVolumeViewProp.SetProperty(volumeProperty);
       mVolumeViewProp.Update();
   }

On Mon, Jan 3, 2011 at 1:09 PM, Mark Roden <mmroden at gmail.com> wrote:
> 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
>