[Insight-users] confusion with specifying origin for 3D affine transformations - itkAffineTransform

[Marius Staring]

Hi Rama,

you have to use SetCenter(centerpoint) and not SetOrigin(). Make sure to 
give centerpoint in world coordinates.

Regards,

Marius Staring

rama wrote:

> Hi,
>
> I have a problem rotating a 3D image about ITS OWN center point around 
> X axis (take that Z axis is pointing into the screen).
>
> I have a 3D image with dimensions as 160 X 144 X 208 pixels in X, Z 
> and Y axis respectively.
>
> I want to rotate this image around X axis about its own center point, 
> that is, around the middle point of the image - (80, 72, 104).  That 
> is, the image should rotate around itself about X-Axis.
> But I am not getting that effect. The image is always rotating around 
> the point (0, 0, 0) of the array index.
>
> Here are the details.
>
> I am importing data from a C++ array like this using 
> itk::ImportImageFilter class.
>
> typedef itk::ImportImageFilter<InputPixelType, Dimension> 
> ImportImgFromArray;
> ImportImgFromArray::Pointer importFilter = ImportImgFromArray::New();
> ImportImgFromArray::SizeType size;
> size[0]=xNumPixels;          //160
> size[1]=yNumPixels;          //208
> size[2]=zNumPixels;          //144
> ImportImgFromArray::IndexType start;
> start.Fill(0);
> ImportImgFromArray::RegionType region;
> region.SetIndex(start);
> region.SetSize(size);
> importFilter->SetRegion(region);
> double origin[Dimension];
> origin[0]=(xNumPixels/2) * PixelXWidth;
> origin[1]=(yNumPixels/2) * PixelYWidth;
> origin[2]=(zNumPixels/2) * PixelZWidth;
> importFilter->SetOrigin(origin);
> double spacing[Dimension];
> spacing[0]=PixelXWidth;
> spacing[1]=PixelYWidth;
> spacing[2]=PixelZWidth;
> importFilter->SetSpacing(spacing);
> importFilter->SetImportPointer(tempBuffer, size[0]*size[1]*size[2], 
> false);      //get data from a tempBuffer - a C++ array - there is no 
> error here
>
> I am setting the transformation like this,
>
> typedef itk::AffineTransform<double, Dimension> TransformType;
> TransformType::Pointer transform=TransformType::New();
>
> resampler->SetDefaultPixelValue(0);      //resampler is a 
> itk::ResampleImageFilter class
> resampler->SetSize(size);
> origin[0]=(xNumPixels/2) * PixelXWidth;
> origin[1]=(yNumPixels/2) * PixelYWidth;
> origin[2]=(zNumPixels/2) * PixelZWidth;
> resampler->SetOutputOrigin(origin);
> resampler->SetOutputSpacing(spacing);
>
> TransformType::OutputVectorType translation1;
> translation1[0]=-origin[0];
> translation1[1]=-origin[1];
> translation1[2]=-origin[2];
> transform->Translate(translation1);
>
> TransformType::OutputVectorType rotation;
> rotation[0]=1;   //rotate around X-Axis
> rotation[1]=0;
> rotation[2]=0;
> transform->Rotate3D(rotation, 
> m_cmnData->SagittalRotateZ(m_curDataSetListSel)*DegToRad, false);
>
> TransformType::OutputVectorType translation2;
> translation2[0]=origin[0];
> translation2[1]=origin[1];
> translation2[2]=origin[2];
> transform->Translate(translation2);
> resampler->SetTransform(transform);
>
> resampler->SetInput(importFilter->GetOutput());
> resampler->Update();
>
> These are my transformation settings. But when I try to rotate it 
> 10degrees either CW or CCW, I am getting the rotations around the 
> array index (0,0,0) not through the point that I specified in the image.
>
> I was skeptical about the before and after translations of the 
> rotation. So, when I disabled those two translations before and after 
> it, the image just went out of bounds and I get only a blank 3D cube.
> When I made the origin point to (0.0, 0.0, 0.0) even then the image is 
> just rotating around the array index (0,0,0).
>
> Can you please suggest me how can I get rotations for the 3D cube 
> around its center point (that is, the center point of the cube). I 
> want the whole cube rotate around itself about X-Axis. Can you please 
> suggest me what to do for that.
>
> thank you,
> Rama Aravind.
>
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> Insight-users at itk.org
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>

-- 
Marius Staring
Image Sciences Institute
University Medical Centre Utrecht
Heidelberglaan 100, 3584 CX Utrecht, The Netherlands
phone: +31 (0)30 250 3186, fax: +31 (0)30 251 3399
marius at isi.uu.nl, http://www.isi.uu.nl/People/Marius