[ITK-users] [ITK] AffineTransform to 4x4 matrix...again maybe

[Matt McCormick]

Hi Vincent,

The values can also be used directly in the matrix as demonstrated here [1].

HTH,
Matt

[1] https://gist.github.com/thewtex/8712205

On Tue, Aug 5, 2014 at 10:08 PM, vincent ngai <vincent.ngai at gmail.com> wrote:
> Hi Bradley,
>
> Hmm, GetCenter() negated should be the same as InvCRM. I'll flip the order
> of the multiplication and see what happens, it could be the C++ operator*()
> order being different from the way its written. Its so annoying to get the
> results close but not exact :(
>
> Thanks
>
>
> On Tue, Aug 5, 2014 at 9:12 PM, Bradley Lowekamp <blowekamp at mail.nih.gov>
> wrote:
>>
>> Hello,
>>
>> That looks pretty close, but I think CRM[12,13,14] should be -GetCenter(),
>> with the negative there.  Then the TM should be applied last, using your
>> original notation with the previously mentioned correction I'd expect this
>> to be correct:
>>
>> OGLM = TM * InvCRM * Rot * CRM
>>
>> Hope that helps,
>> Brad
>>
>> [1]
>> http://www.itk.org/Doxygen/html/classitk_1_1MatrixOffsetTransformBase.html
>>
>> On Aug 5, 2014, at 5:26 AM, vincent ngai <vincent.ngai at gmail.com> wrote:
>>
>> > Hi all, apologies if this has been asked before, I googled the above but
>> > only got 4x4 -> AffineTransform and not the other way around.
>> >
>> > I need to get the output of an AffineTransform after registration to my
>> > OpenGL renderer.
>> >
>> > From what I understand, the AffineTransform is composed of a Rotation,
>> > Center of Rotation and Translation.
>> >
>> > So would the following sequence of 4x4 transformation be correct?
>> >
>> > OGLM = InvCRM * Rot * CRM * TM
>> >
>> > where
>> >
>> > CRM      = 4x4 identity matrix with indices [ 12, 13, 14] set to XYZ
>> > value of GetCenter()
>> > InvCRM  = Inverse of CRM
>> > Rot        = 4x4 Identity matrix with 3x3 set to the rotation parameters
>> > TM        = 4x4 identity matrix with indicies[ 12, 13, 14 ] set to the
>> > translation parameters
>> >
>> > Essentially:
>> >
>> > 1) translate center to origin
>> > 2) perform rotation
>> > 3) translate back to where we were
>> > 4) slap on translation
>> >
>> > I am doing the above, but for some reason the translation does not match
>> > up. The rotation seems fine.
>> > --
>> > Regards,
>> > Vincent
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>
>
>
> --
> Regards,
> Vincent
>
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