[vtkusers] Reslicer rotation axis

[David Gobbi]

Hi Fabian,

Calling SetResliceAxesOrigin() is the wrong thing to do here.

If you want to rotate around a specific point, you need to build a
transform matrix that does the following:
1) translate by (- P) where P is the desired centre of rotation
2) rotate
3) translate by P (the same P as above)

Define T as the matrix that translates by -P,
define R as the pure rotation matrix, and
define U as the matrix that translates by P:

  M = U R T

The special property of this matrix is that it does not change the
point that is defined as the centre of rotation:

  M P == P

So you should build matrix M and then call SetResliceAxes(M).

 - David


On Fri, May 27, 2016 at 1:26 PM, Fabian Torres <fabian.trobles at gmail.com>
wrote:

> Hi all.
>
> I have a volume and I want to extract the center sagital slice of the
> volume and rotate it around the x axis in the center of the image. For this
> I'm using vtkImageReslice and vtkTransform.
> Everything works fine until I rotate the slice. It is rotating around the
> origin of the output image (lower left corner of the image) and not through
> the center of it. Can any one explain to me how do I choose the rotation
> axis in the transform. here is a brief of my code.
>
> const double MainWindow::sagitalElements[16] = {
> 0, 0, 1, 0,
> 1, 0, 0, 0,
> 0, 1, 0, 0,
> 0, 0, 0, 1
> };
>
> volumeData->GetSpacing(spacing);
> volumeData->GetOrigin(origin);
> volumeData->GetDimensions(dimensions);
>
> centerSlice[0] = floor(dimensions[0]*0.5);
> centerSlice[1] = floor(dimensions[1]*0.5);
> centerSlice[2] = floor(dimensions[2]*0.5);
>
> positionCenter[0] = origin[0] + spacing[0] * centerSlice[0];
> positionCenter[1] = origin[1] + spacing[1] * centerSlice[1];
> positionCenter[2] = origin[2] + spacing[2] * centerSlice[2];
>
> resliceAxesSagital->DeepCopy(sagitalElements);
>
> transformSagital->RotateX(rotate);
>
> reslicerSagital->SetInput(volumeData);
> reslicerSagital->SetOutputDimensionality(2);
> reslicerSagital->SetResliceAxes(resliceAxesSagital);
> reslicerSagital->SetResliceAxesOrigin(positionCenter);
> reslicerSagital->SetInterpolationModeToLinear();
>
> reslicerSagital->SetResliceTransform(transformSagital);
> reslicerSagital->Update();
> sliceImageSagital = reslicerSagital->GetOutput();
>
>
> As I dsaid before the problem is that I want to rotate around the
> center of the image and not the origin of the image.
>
>
> Thanks a lot
>
>
> --
> Fabián Torres Robles
> Maestria en Ciencias en Ingeniería Electrónica
> Ingeniería en Sistemas Electrónicos
> tel. 58081280, 0445534661338
> e-mail fabian.trobles at gmail.com, dae.wong at gmail.com
>
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