[ITK-users] Applying transform with a rotation, translation, and offset to points

[Andrew Harris]

Hi Matt,
Thanks for getting back to me.  I’m still a bit foggy about the
relationship between matrix, offset, and translation.  I think I’m going to
try and mark my targets within ITK and transform them as you have
suggested, outputting a text file to then analyze.  However, I would like
to know what is going on “under the hood” so to speak, just in case someone
asks me to explain it. If I were to compose a 4x4 transformation matrix
using the 3x3 matrix and 3x1 offset, apply it to a point, and then add the
3x1 translation after the fact would that correctly transform the point?


--

AH


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On Wed, Mar 22, 2017 at 5:00 PM, Matt McCormick <matt.mccormick at kitware.com>
wrote:

> Hello Andrew,
>
> To apply the transformation, typically the methods,
>
>   itk::Image::TransformIndexToPhysicalPoint
>   itk::Transform::TransformPoint
>
> would be used.
>
>
> Nonetheless, a matrix representation from VersorRigid3DTransform can
> be obtained from its base class methods
> itk::MatrixOffsetTransformBase::GetMatrix and
> itk::MatrixOffsetTransformBase::GetOffset.
>
> HTH,
> Matt
>
> On Wed, Mar 22, 2017 at 3:15 PM, Andrew Harris <aharr8 at uwo.ca> wrote:
> > Hello,
> > I would like to be able to duplicate the applicaiton of a
> > VersorRigid3DTransform that incorporates a rotation, translation, and
> offset
> > to points selected to calculate TRE between a fixed and transformed
> moving
> > image.  I’m confused about how the 3x3 matrix, 3x1 transform, and 3x1
> offset
> > are applied within a ResampleFilter.  If I could get them composed into a
> > 4x4 transform matrix I could apply that to the points selected in the
> moving
> > image and calculate the distance between the transformed points and the
> > corresponding points in the fixed image.  Any help would be appreciated.
> >
> > --
> >
> > AH
> >
> >
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