[vtkusers] volume rendering a data with multiple components

[chenjianfeng]

I have been doing volume rendering using vtkImageData with one component. Now I want to make a new vtkImageData based on the existing one. The new vtkImageData has two components and the first component store the scalar data the same as the existing one, the second component store the data which I will assign. A fragment of my code is like this:
 
 
 
vtkImageData *originalData = reader->GetOutput(); // I read a series of dicom file.
 
 
 
    int dim[3];
 
    double spa[3], ori[3];
 
originalData->GetDimensions(dim);
 
originalData->GetSpacing(spa);
 
originalData->GetOrigin(ori);
 
 
 
vtkImageData *newData = vtkImagaData::New();//newData is created based on the               originalData's dimensions spacing and origin.
 
 
 
    newData->SetDimensions(dim);
 
newData->SetScalarTypeToShort();
 
newData->SetSpacing(spa);
 
newData->SetNumberOfScalarComponents(2);//newData's component is two
 
newData->SetOrigin(ori);
 
newData->AllocateScalars();
 
 
 
    //Now I have some puzzles:How does the vtkImageData store multiple components, I think it store data one point by one point, because each point now have two components, so it looks like this in memory: Ponit1(component1, component2), Ponit2(component1, component2), Ponit3.... is it right???
 
    //Then I traverse the new data and assign each component of each point
 
    short *originalDataPointer = (short *)originalData->GetScalarPointer();
 
short *newDataPointer = (short *)newData->GetScalarPointer();
 
for(int i = 0; i < dim[0]*dim[1]*dim[2]; i++){
 
            //I assign each point's first component and second component the same data as the original data.
 
    originalDataPointer[i*2] = newDataPointer[i];
 
            originalDataPointer[i*2 + 1] = newDataPointer[i];
 
 
 
}
 
 
 
    vtkSmartPointer<vtkColorTransferFunction> colorTransferFunction =
 
    vtkSmartPointer<vtkColorTransferFunction>::New();
 
    colorTransferFunction->AddRGBPoint(0.0, 0.0, 0.5, 0.0);
 
colorTransferFunction->AddRGBPoint(60.0, 1.0, 0.0, 0.0);
 
colorTransferFunction->AddRGBPoint(128.0, 0.2, 0.1, 0.9);
 
colorTransferFunction->AddRGBPoint(196.0, 0.27, 0.21, 0.1);
 
colorTransferFunction->AddRGBPoint(255.0, 0.8, 0.8, 0.8);
 
    vtkSmartPointer<vtkPiecewiseFunction> piecewiseFunction =
 
    vtkSmartPointer<vtkPiecewiseFunction>::New();
 
    piecewiseFunction->AddPoint(20, 0.0);
 
    piecewiseFunction->AddPoint(120, 0.1);
 
    piecewiseFunction->AddPoint(255, 0.2);
 
    vtkSmartPointer<vtkFixedPointVolumeRayCastMapper> fixedPointVolumeRayCastMapper =
 
    vtkSmartPointer<vtkFixedPointVolumeRayCastMapper>::New();
 
    fixedPointVolumeRayCastMapper->SetNumberOfThreads(1);
 
 
 
    fixedPointVolumeRayCastMapper->SetInput(newData);
 
    vtkSmartPointer<vtkVolumeProperty> volumeProperty =
 
    vtkSmartPointer<vtkVolumeProperty>::New();
 
    volumeProperty->SetScalarOpacity(0, piecewiseFunction);//I want to use the first component as the input of opacity transfer function
 
    volumeProperty->SetColor(1, colorTransferFunction);// I want to use the second component as the input of color transfer function
 
 
 
    vtkSmartPointer<vtkVolume> volume = vtkSmartPointer<vtkVolume>::New();
 
    volume->SetMapper(fixedPointVolumeRayCastMapper);
 
    volume->SetProperty(volumeProperty);
 
 
 
    vtkSmartPointer<vtkOpenGLRenderer> renderer =
 
    vtkSmartPointer<vtkOpenGLRenderer>::New();
 
    renderer->AddVolume(volume);
 
 
 
    vtkSmartPointer<vtkRenderWindow> renWin =
 
    vtkSmartPointer<vtkRenderWindow>::New();
 
    renWin->AddRenderer(renderer);
 
    renWin->Render(); 
 
 
 
   [the result of the volume rendering is diffrent from the result of the original data which only has one component with the same transfer function. Shouldn't the result be the same?
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