[vtkusers] Problems with multi volume rendering with VTK.

[Stephane]

Hello,

I'm new to VTK (using it with java) and i'm trying to do multiple volume rendering.
I've a 3D grid data structure which can be of any data type (char, short, int, float, double...) and with 1 or more component (usually 1 component represent one color, i called it 'band' in my code).
I tried severals methods to draw that dataset but none of them satisfy me.
With the following code, i'm creating severals volume when i've severals components / bands in my grid data structure. The problem is that depth intersection is wrong between different volumes. I tried to use multi component volume rendering but it doesn't work with some volume mappers (afaik it works only with the vtkFixedPointVolumeRayCastMapper  mapper for me).

    private final vtkRenderer renderer;
    ...

    private void createVolumeFromSequence(boolean raytrace, int band)
    {
       vtkVolumeMapper volumeMapper;
       vtkVolume volume = new vtkVolume();
       vtkVolumeProperty volumeProperty = new vtkVolumeProperty();;
       vtkImageData imageData = new vtkImageData();

       if (raytrace)
       {
           // ACCURATE VISUALIZATION MODE
           volumeMapper = new vtkFixedPointVolumeRayCastMapper();
           ((vtkFixedPointVolumeRayCastMapper) volumeMapper).IntermixIntersectingGeometryOn();
       }
       else
       {
           // FAST VISUALIZATION MODE
           volumeMapper = new vtkOpenGLVolumeTextureMapper2D();
       }

       buildImageData(imageData, band);
       setupColorProperties(volumeProperty, lut.getLutBand(band));

       volumeMapper.SetInput(imageData);

       volume.SetMapper(volumeMapper);
       volume.SetProperty(volumeProperty);

       renderer.AddVolume(volume);
    }

    private void buildImageData(vtkImageData imageData, int band)
    {
        final Sequence sequence = getSequence();
        final int sizeX = sequence.getSizeX();
        final int sizeY = sequence.getSizeY();
        final int sizeZ = sequence.getSizeZ();
        final int dataType = sequence.getDataType();
        final int posT = getT();

        imageData.SetDimensions(sizeX, sizeY, sizeZ);
        imageData.SetNumberOfScalarComponents(1);
        imageData.SetSpacing(1, 1, 5);
        imageData.SetWholeExtent(0, sizeX - 1, 0, sizeY - 1, 0, sizeZ - 1);

        switch (dataType)
        {
            case DataBuffer.TYPE_BYTE:
            {
                imageData.SetScalarTypeToUnsignedChar();
                // pre-allocate data
                imageData.AllocateScalars();
                // get array structure
                final vtkDataArray array = imageData.GetPointData().GetScalars();
                // set frame sequence data in the array structure
                ((vtkUnsignedCharArray) array).SetJavaArray(sequence.getComponentDataAsByteArray(band));
                break;
            }

            case DataBuffer.TYPE_SHORT:
            {
                imageData.SetScalarTypeToShort();
...
            }
        }

        imageData.UpdateData();
        imageData.UpdateInformation();
    }


    private void setupColorProperties(vtkVolumeProperty volumeProperty, LUTBand lutBand)
    {
//         volumeProperty.IndependentComponentsOn();
         volumeProperty.SetInterpolationTypeToLinear();
         volumeProperty.DisableGradientOpacityOn();

        XXXToRGBColorMap colorMap = lutBand.getColorMap();
        Scaler scaler = lutBand.getScaler();

        // SCALAR COLOR FUNCTION
        vtkColorTransferFunction ctf = new vtkColorTransferFunction();

        ctf.SetRange(scaler.getMinIn(), scaler.getMaxIn());
        for (int i = 0; i < XXXToRGBColorMap.COLORMAP_SIZE; i++)
            ctf.AddRGBPoint(scaler.unscale(i), colorMap.rf[i], colorMap.gf[i], colorMap.bf[i]);

        volumeProperty.SetColor(ctf);

        // SCALAR OPACITY FUNCTION
        vtkPiecewiseFunction pwf = new vtkPiecewiseFunction();

         pwf.AddPoint(0, 0);
         pwf.AddPoint(32, 0.02);
         pwf.AddPoint(255, 0.4);

        volumeProperty.SetScalarOpacity(pwf);
    }


VTK seems to be a very powerful but also very complex visualization library when you discover it. I'm sure i'm doing things in the wrong way and but i can't find any examples of what i'm trying to do. Can someone give me some light on my problem please ? Thanks by advance =)

- Stephane



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