[vtkusers] Re: Rotation does not happen about the center of the image

[Anja Ende]

Ok, here is basically what I do...

I have just tried to get the code that might be relevant here to demonstrate
the problem.

// Read the image
vtkDICOMImageReader * reader = vtkDICOMImageReader::New();
reader->SetDirectoryName("/home/anja/data/dicom/11088");
reader->Update();

// Apply the vtkImageChangeInformation filter
vtkImageChangeInformation * imageChangeInformation =
vtkImageChangeInformation::New();
imageChangeInformation->SetInput(reader->GetOutput());
imageChangeInformation->CenterImageOn(); // Centered the image here....
imageChangeInformation->Update();

vtkImageReslice * reslice = vtkImageReslice::New();
reslice->SetOutputDimensionality(2);
vtkTransform * transform = vtkTransform::New();
transform->Identity();
reslice->SetResliceTransform(transform);

reslice->SetInput(imageChangeInformation->GetOutput());

// Assume that the origin and spacing are set from the input data...num is
the Z slice index that
// we want to show

this->m_slicer->SetResliceAxesOrigin(0, 0, origin[2] + num * spacing[2]);

Now if I tell the transform to rotate along the z axes, it should rotate
about the center, right?

transform->RotateZ();

However, this rotation does not seem to be happening about the center...

Stangely though,

transform->Scale(factor, factor, 1.0);

scales correctly...i.e. the scaling is applied uniformly from the center...

I have a pretty urgent requirement and I need to fix this as soon as
possible. So, any help would be really appreciated.

Thanks,
Anja


On 18/09/06, Anja Ende <anja.ende at googlemail.com> wrote:
>
> Hi,
>
> This is kinda bizarre. I verified that the zooming (scaling in the
> transform) happens around the center but the rotation does not...the
> rotation happens as if the vtkImageChangeInformation filter has not been
> applied at all...
>
> Did anyone else notice this ?? is there something special I have to do for
> rotations???
>
> Cheers,
> Anja
>
>
> On 18/09/06, Anja Ende < anja.ende at googlemail.com> wrote:
> >
> > Hi everyone,
> >
> > I am unsable to have the rotations at the center of the image.
> >
> > So, I have a 3D volume and I pass it through the
> > vtkImageChangeInformation filter. The CenterImageOn() function si called.
> >
> > The output of this filter is passed to a vtkImageReslice which has a
> > transformation object that does the scaling and rotation. The scaling works
> > fine but when I rotate the image I can see the center being shifyted. I
> > thought that the vtkTransform should do these operations around the image
> > center.
> >
> > I printed the vtkImageReslice index matrix and the original matrix is:
> >
> > Elements:
> >  1 0 0 0
> >  0 1 0 0
> >  0 0 1 62
> >  0 0 0 1
> >
> > And after a rotation of one degree:
> >
> > 0.999848        -0.0174524 0            0.0776696
> > 0.0174524       0.999848 0              -4.44969
> >   0 0 1 62
> >   0 0 0 1
> >
> > I was hoping that the center would remain stationary....
> >
> > If anyone can cast some light on how I can manage this, I would be
> > really grateful.
> >
> > Thanks,
> > Anja
> >
> >
>
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