[ITK-users] [ITK] applying a transform to an ITK Point object results in it moving the opposite direction from the image

[Andrew Harris]

Thanks for getting back to me.

The numbers correspond correctly to what is expected when I do the math
directly in MATLAB, and when I do the matrix multiplication I get the same
coordinates that are output by ITK for both the translation that works and
the rotation that does not.  One curious note is that while I set the
center of rotation explicitly, it shows up as a zero vector in the output.
I was able to get the known rotation case to match up the expected
coordinates by subtracting newTranslatin()->GetOffset(); from the resulting
point, but then of course the known translation case fails.

Any further thoughts would be appreciated.

--

AH


Andrew Harris, Honours BSc (Medical Physics)

PhD (CAMPEP) & MClSc Candidate

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On Thu, Jun 29, 2017 at 3:04 PM, Yaniv, Ziv Rafael (NIH/NLM/LHC) [C] <
zivrafael.yaniv at nih.gov> wrote:

> The code snippet looks correct. I would advise that you print the
> transformations to see that you are getting what you expect. The relevant
> entries, Matrix, Center, Translation, Offset:
>
>
>
> Original transform is:
>
>
>
> *T*(*x*)=*A*(*x*−*c*)+*t*+*c*
>
>
>
> Where:
>
> *A* – matrix
>
> *c* – center
>
> *t *– translation
>
> *t**+c –A**c* – offset
>
>
>
> The inverse should have:
>
> *A*^{-1} – matrix
>
> *c* – center
>
> -*A*^{-1}* t *– translation
>
> *c* - *A*^{-1}* t - **A*^{-1}* c* - offset
>
>
>
>
>
>         hope this helps
>
>                   Ziv
>
>
>
> p.s. When working with ITK always remember that you are dealing with
> physical space, distances are in mm/km…, volumes in mm^3…. Don’t be tempted
> to measure things in pixels/voxels.
>
>
>
> *From: *Andrew Harris <aharr8 at uwo.ca>
> *Date: *Thursday, June 29, 2017 at 1:21 PM
> *To: *"Yaniv, Ziv Rafael (NIH/NLM/LHC) [C]" <zivrafael.yaniv at nih.gov>
> *Cc: *Insight-users <insight-users at itk.org>
> *Subject: *Re: [ITK-users] [ITK] applying a transform to an ITK Point
> object results in it moving the opposite direction from the image
>
>
>
> Thanks for getting back to me. Using the inverse transform on the point
> selected in the moving image works to transform the point within a
> reasonable amount to the homologous feature selected in the fixed image
> when I use two identical images with a known offset of 100 voxels in each
> direction.  However, upon testing identical images with a known rotation
> the selected points again fail to line up.  The transform I have been using
> is the Rigid3DVersorTransform, and the lines of code I'm using to set the
> inverse are:
>
>
>
> newTransform->SetCenter(oldTransform->GetCenter());
>
> oldTransform->GetInverse(newTransform);
>
>
>
> Any idea why translation would work but rotation causes a problem?
>
>
> --
>
> AH
>
>
>
> Andrew Harris, Honours BSc (Medical Physics)
>
> PhD (CAMPEP) & MClSc Candidate
>
> ------------------------------------------------------------
> -----------------------------------
>
> *This email and any attachments thereto may contain private,
> confidential, and privileged materials for the sole use of the intended
> recipient. Any reviewing, copying, or distribution of this email (or any
> attachments thereto) by other than the intended recipient is strictly
> prohibited. If you are not the intended recipient, please contact the
> sender immediately and permanently destroy this email and any attachments
> thereto.*
>
>
>
> On Wed, Jun 28, 2017 at 4:50 PM, Yaniv, Ziv Rafael (NIH/NLM/LHC) [C] <
> zivrafael.yaniv at nih.gov> wrote:
>
> Hello Andrew,
>
>
>
> In ITK the result of a registration maps points from the fixed image
> coordinate system to the moving coordinate system, so T(p_f) = p_m and the
> TRE is || T(p_f) – p_m||. I suspect you just need to use the inverse
> transform.
>
>
>
> You may be interested in this SimpleITK notebook (http://
> insightsoftwareconsortium.github.io/SimpleITK-Notebooks/
> Python_html/67_Registration_Semiautomatic_Homework.html) which has a
> linked cursor GUI (gui. RegistrationPointDataAquisition). The source code
> for the UI is here: https://github.com/InsightSoftwareConsortium/
> SimpleITK-Notebooks/blob/master/Python/gui.py .
>
>
>
>       hope this helps
>
>              Ziv
>
>
>
>
>
>
>
>
>
> *From: *Andrew Harris <aharr8 at uwo.ca>
> *Date: *Wednesday, June 28, 2017 at 3:14 PM
> *To: *Insight-users <insight-users at itk.org>
> *Subject: *[ITK-users] [ITK] applying a transform to an ITK Point object
> results in it moving the opposite direction from the image
>
>
>
> Hi there,
>
> I have been trying for a while to get this working: I want to be able to
> select corresponding points in a fixed and moving image, and determine how
> well the moving image is transformed to overlay the fixed image by using
> target registration error.  The problem is, using the same transform I
> applied to a moving image that translated it to the left, the point
> selected in the moving image gets translated to the right for example.
>
> --
>
> AH
>
>
>
> Andrew Harris, Honours BSc (Medical Physics)
>
> PhD (CAMPEP) & MClSc Candidate
>
> ------------------------------------------------------------
> -----------------------------------
>
> *This email and any attachments thereto may contain private,
> confidential, and privileged materials for the sole use of the intended
> recipient. Any reviewing, copying, or distribution of this email (or any
> attachments thereto) by other than the intended recipient is strictly
> prohibited. If you are not the intended recipient, please contact the
> sender immediately and permanently destroy this email and any attachments
> thereto.*
>
>
>
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