[vtkusers] Displaying a 2D image as a volume

[Cory Quammen]

Jeroen,

Does the thickness of the image change across the image? If so, why
not display the image as a height field? You could even distort the
image by a positive factor to get one surface and by a negative factor
to get a back surface. When you place the surfaces back-to-back, you
will get a shape with some thickness. The only problem is that the
edges of the two height fields might not meet if there is non-zero
displacement at the edges, but you could work around that if it
bothers you.

Cory

On Wed, Feb 27, 2008 at 11:06 AM,  <J.S.Wijnhout at lumc.nl> wrote:
> >Dimension[i] is the number of points along axis i, not the number of cells. >Number of cells along axis i is Dimension[i]-1. If Dimension[i]=1, number >of cells[i]=0, so no thickness.
>
>  Thanks for clearing that up. Do you have an idea of how to display the slice (which has a thickness in reality), without resorting to padding?
>
>  best,
>  Jeroen
>
>
>
>  J.S.Wijnhout at lumc.nl wrote:
>  > Hi,
>  >
>  > Thanks for the suggestion, that actually worked! I'm not sure what is
>  > wrong with my original approach (a bug perhaps?), but padding the image
>  > with transparent voxels work. For those of you who have the same
>  > problem:
>  >
>  >     double minValue = _image->GetScalarTypeMax ();
>  >     double maxValue = _image->GetScalarTypeMin ();
>  >     // This is a custom function to determine the min/max gray values:
>  >     DetermineMinMax ( _image, minValue, maxValue );
>  >     vtkImageShiftScale *scaler = vtkImageShiftScale::New ();
>  >     scaler->SetInput ( _image );
>  >     scaler->SetOutputScalarTypeToUnsignedChar ();
>  >
>  >     // Map to [1,255], the value 0 is reserved for a transparency hack:
>  >     int delta = maxValue - minValue;
>  >     scaler->SetShift ( ( delta / 254.0 ) - minValue );
>  >     scaler->SetScale ( 254.0 / delta );
>  >
>  >
>  >     vtkImageConstantPad *padder = vtkImageConstantPad::New ();
>  >     int extent [ 6 ];
>  >     _image->GetExtent ( extent );
>  >     extent [ 2 ] = 3;
>  >     extent [ 5 ] = 3;
>  >     padder->SetOutputWholeExtent ( extent );
>  >     padder->SetInput ( scaler->GetOutput () );
>  >     padder->SetConstant ( 0.0 );
>  >
>  >     // Modify the transfer functions such that pixel value 0 (the
>  >     // value the image is padded with in the z-dimension) corresponds to
>  > a
>  >     // completely transparent voxel and value 1 to pure black:
>  >     vtkPiecewiseFunction *opacityTransferFunction =
>  > vtkPiecewiseFunction::New ();
>  >     opacityTransferFunction->AddPoint ( 0, 0.0 );
>  >     opacityTransferFunction->AddPoint ( 0.5, 1.0 );
>  >     opacityTransferFunction->AddPoint ( 1, 1.0 );
>  >     opacityTransferFunction->AddPoint ( 255, 1.0 );
>  >     vtkColorTransferFunction *colorTransferFunction =
>  > vtkColorTransferFunction::New ();
>  >     colorTransferFunction->AddRGBPoint ( 0, 0.0, 0.0, 0.0 );
>  >     colorTransferFunction->AddRGBPoint ( 1, 0.0, 0.0, 0.0 );
>  >     colorTransferFunction->AddRGBPoint ( 255, 1.0, 1.0, 1.0 );
>  >
>  >     vtkVolumeProperty *volumeProperty = vtkVolumeProperty::New ();
>  >     volumeProperty->SetColor ( colorTransferFunction );
>  >     volumeProperty->SetScalarOpacity ( opacityTransferFunction );
>  >
>  >     vtkVolumeRayCastCompositeFunction *rayCastFunction =
>  > vtkVolumeRayCastCompositeFunction::New ();
>  >
>  >     vtkVolumeRayCastMapper *hiResVolumeMapper =
>  > vtkVolumeRayCastMapper::New ();
>  >     hiResVolumeMapper->SetInput ( padder->GetOutput () );
>  >     hiResVolumeMapper->SetVolumeRayCastFunction ( rayCastFunction );
>  >
>  >     vtkVolume *volume = vtkVolume::New ();
>  >     volume->SetProperty ( volumeProperty );
>  >     volume->SetMapper ( hiResVolumeMapper );
>  >
>  >
>  > best,
>  > Jeroen
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>
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-- 
Cory Quammen
Department of Computer Science
University of North Carolina at Chapel Hill
http://www.cs.unc.edu/~cquammen