# Affine Transform: Offset vs. fixed center

**URL:** <https://discourse.itk.org/t/affine-transform-offset-vs-fixed-center/5721>\
**Category:** Algorithms\
**Tags:** itk, simpleitk, registration\
**Created:** [February 17, 2023, 9:21pm UTC](https://discourse.itk.org/t/affine-transform-offset-vs-fixed-center/5721 "2023-02-17T21:21:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![elapins](https://discourse.itk.org/letter_avatar_proxy/v4/letter/e/96bed5/32.png) [@elapins](https://discourse.itk.org/u/elapins)\
**Post date:** [February 17, 2023, 9:21pm UTC](https://discourse.itk.org/t/affine-transform-offset-vs-fixed-center/5721/1 "2023-02-17T21:21:35Z")

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When initializing an affine transform for a registration framework, what is the difference between the offset and the fixed center inputs?

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**Author:** ![zivy](https://discourse.itk.org/user_avatar/discourse.itk.org/zivy/32/1726_2.png) [@zivy](https://discourse.itk.org/u/zivy)\
**Post date:** [February 17, 2023, 10:39pm UTC](https://discourse.itk.org/t/affine-transform-offset-vs-fixed-center/5721/2 "2023-02-17T22:39:42Z")

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Hello @elapins,

Please see [this jupyter notebook](https://github.com/InsightSoftwareConsortium/SimpleITK-Notebooks/blob/master/Python/22_Transforms.ipynb) for all the details with respect to spatial transformation.

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<div class="post-metadata">

**Author:** ![elapins](https://discourse.itk.org/letter_avatar_proxy/v4/letter/e/96bed5/32.png) [@elapins](https://discourse.itk.org/u/elapins)\
**Post date:** [February 18, 2023, 4:12pm UTC](https://discourse.itk.org/t/affine-transform-offset-vs-fixed-center/5721/3 "2023-02-18T16:12:39Z")

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I think i am just confused about initializing. Because when I use an exhaustive search without initialization, the images register incorrectly but biased in the top left corner (image origin).

So I am wondering how I can get this to either a) actually search the full image, or b) initialize it closer to the answer using known locations?

Thank you!!