[vtkusers] voxel values in vtkImageData

Fri May 7 14:26:59 EDT 2004

Hello Thomas,

No - it is not useless - it is just not used by every mapper. The ray cast 
mapper can do either. I believe the VolumePro mapper only does one (linear) 
because at the time the mapper was written nearest was unstable. The 
texture mapper only does linear but it not a hard change to make it do 
nearest as well.

Lisa

At 11:39 AM 5/7/2004, Thomas Faust wrote:

>Does this mean, the interpolation type in vtkVolumeProperty (nearest vs.
>linear) is useless? It only depends on the mapper I use?
>
>
>On Friday 07 May 2004 10:24 am, you wrote:
> > Hello Thomas,
> >
> > Please keep in mind that the vtkVolumeRayCastMapper does nearest neighbor
> > sampling, but the vtkVolumeTextureMapper2D does not (it does bilinear in
> > two dimensions).
> >
> > Lisa
> >
> > At 06:55 PM 5/6/2004, Thomas Faust wrote:
> > > >There is no way to get around that, apart from...
> > >
> > >There is... The last think I would do and the last thing I want to do is
> > > to write my own vtkVolumeMapper, that handles vtkImageData like I want. I
> > > did the same with vtkPicker before. I was writing my own, that runs a ray
> > > through voxels using the 'voxel traversal algorithm'. I made major
> > > changes in vtkRenderWindow and vtkRenderWindowInteractor to implement it
> > > my out GUI. But, this would really be the last thing if no workaound
> > > would help.
> > >
> > > > If you zero-pad your image out to 5x5x5 you might be able to make it
> > > > display a cross the way that you want.
> > >
> > >Thanks for this advice. I'll give it a try by tomorrow. My coffee pot went
> > >empty ;-)
> > >
> > >Thomas
> > >
> > >On Thursday 06 May 2004 06:40 pm, you wrote:
> > > > 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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