[Insight-users] How to set Arbitrary Center of Rotation

[Daniel Blezek]

Hi Mike,

  I usually think of this as a composition of three homogeneous transforms.
If we let C be the point you'd like to rotate around, and T_{R} be the
rotation you want to apply.

T_{all} = T_{C} * T_{R} * T_{-C}

Any point in homogeneous form can be multiplied as:

P' = T_{all} * P

This will first shift the image so it's origin is at the point C, then
rotate about the point, and finally undo the first translation.  The
operations are applied in a right to left order.  (Forgive me if this was
pedantic).

Best regards,
-dan


On 5/6/09 3:52 PM, "Mike Jackson" <mike.jackson at bluequartz.net> wrote:

> I am trying to register  a pair of images. There is a rotation
> involved and I know (through manual means) that the center of rotation
> is somewhere in the upper left of the image. What registration methods
> would support this type of rotation? I have been working through the
> Centered2DRegistration code to try and understand what is going on. It
> would seem like I just need to apply an initial translation to the
> images to get the upper left corner of the image into the "middle" of
> the registration space? Is that correct?
> 
> Thanks

-- 
Daniel Blezek, PhD
Medical Imaging Informatics Innovation Center

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