[vtkusers] voxel values in vtkImageData

[David Gobbi]

Hi Thomas,

The 3-voxels-are-2-voxels-wide problem is something that you can't get
away from in VTK, since as you stated below, VTK treats a vtkImageData as
a set of points.  There is no way to get around that, apart from using
a vtkUnstructuredGrid made of voxels which would be extremely inefficient.
The vtkImageActor has the same behaviour as vtkVolume in this regard.

Turning off interpolation, though, should at least eliminate the
unwanted blending that you were seeing.
If you zero-pad your image out to 5x5x5 you might be able to make it
display a cross the way that you want.

 - David


On Thu, 6 May 2004, Thomas Faust wrote:

>
> Thanks David, but this doesn't solve my problem at all.
>
> I was changing the interpolation method back and for, but the output didn't
> changed.
>
> I'm not dealing with values that are defined on the gridpoints; my values are
> the voxel itself.
>
> I'll give you (David and all out there) an example:
> My matrix is 3x3x3 with the values: 000 010 000 - 010 111 010 - 000 010 000
> Do I expect to much brain grease if i would ask you to picture this values in
> your imagination in 3D? Right, this is an 3D cross.
> But, if this is my vtkImageData I'll get a volume, that is just 2 voxels in
> each direction. Please give it a try. (I'll at the 15 line source code if you
> want me to)
>
> What I'd like to see as an output is an volume, that comes with 27 (3x3x3)
> voxel. This means that this volume would have 64 (4x4x4) gridpoints. What I
> told about interpolation is, that i can't interpolate these 64 gridpoints out
> of the 27 values to create my own new vtkImageData.
> It's all about the interpretation of values in vtkImageData by
> vtkVolumeMapper.
>
> Thanks for your efforts.
> Thomas
>
> On Thursday 06 May 2004 05:56 pm, you wrote:
> > Hi Thomas,
> >
> > It looks like all you need to do is turn off interpolation:
> >
> > volume->GetProperty()->SetInterpolationTypeToNearest();
> >
> > On Thu, 6 May 2004, Thomas Faust wrote:
> > > Hi VTK users,
> > >
> > > Lately I'm confronted with volume rendering. I decided to use VTK as
> > > graphical tool to render a huge mass of data. So far, I'm impressed by
> > > the power and usability of VTK.
> > >
> > > My problem is the handling of vtkImageData in vtkVolumeMapper.
> > > My model is created by a collection of values in 3 directions (x,y,z).
> > > These are stored in vtkImageData.
> > > I expect a volume that extent 3 values(voxels) in each direction to be 3
> > > length units long. But it isn't (It's just 2). The reason for this is,
> > > that the vtkVolumeMapper interprets 3 points in one direction as 3 corner
> > > points (vertices) of voxels. So I end up with 2 voxels that are a mixture
> > > between my original values.
> > >
> > > The problem is that a interpolation between these values is not a option,
> > > because two values that are even close together means totaly different
> > > things. (e.g. 0x40 is material A, 0x41 is material B)
> > >
> > > How can I change one of the vtkVolumeMappers to interpret the values in
> > > vtkImageData to be voxel-based and not vertex-based?
> > >
> > > Any comments are welcome and will be answered.
> > > Thanks in advance
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