# CenteredTransformInitializer with only TranslationTransform?
**URL:** https://discourse.itk.org/t/centeredtransforminitializer-with-only-translationtransform/4635
**Category:** Beginner Questions
**Tags:** registration, python, simpleitk
**Created:** [December 3, 2021, 4:16pm UTC](https://discourse.itk.org/t/centeredtransforminitializer-with-only-translationtransform/4635 "2021-12-03T16:16:02Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@sdbonte](https://discourse.itk.org/u/sdbonte)
#### Post date: [December 3, 2021, 4:16pm UTC](https://discourse.itk.org/t/centeredtransforminitializer-with-only-translationtransform/4635/1 "2021-12-03T16:16:02Z")
I am trying to register two 3D CT scans using SimpleITK. After checking they have the same orientation, I load them from .nii.gz files. Then they look like this (central axial slice displayed):
Fixed image:
Moving image:
To initialize the registration, following [this tutorial](https://simpleitk.org/SPIE2019_COURSE/04_basic_registration.html) we first need to align the two volumes. However, after doing this:
```auto
initial_transform = sitk.CenteredTransformInitializer(fixed_image,
moving_image,
sitk.Euler3DTransform(),
sitk.CenteredTransformInitializerFilter.GEOMETRY
)
moving_resampled = sitk.Resample(moving_image, fixed_image, initial_transform, sitk.sitkLinear, 0.0, moving_image.GetPixelID())
```
The moving\_resampled image is flipped upside down:
Is this normal behavior?
As an alternative, I tried to just align the images using a 3D translation, which gives an error:
```auto
initial_transform = sitk.CenteredTransformInitializer(fixed_image,
moving_image,
sitk.TranslationTransform(3),#sitk.Euler3DTransform(),
sitk.CenteredTransformInitializerFilter.GEOMETRY,
) # .MOMENTS)
moving_resampled = sitk.Resample(moving_image, fixed_image, initial_transform, sitk.sitkLinear, 0.0, moving_image.GetPixelID())
```
**File “C:\Users\stijnb\AppData\Local\Continuum\miniconda3\envs\mimicsenv352\lib\site-packages\SimpleITK\SimpleITK.py”, line 6169, in CenteredTransformInitializer**
\*\*return \_SimpleITK.CenteredTransformInitializer(\*args, **kwargs)**
**RuntimeError: Exception thrown in SimpleITK CenteredTransformInitializer: D:\a\1\sitk\Code\BasicFilters\src\sitkCenteredTransformInitializerFilter.cxx:132:**
**sitk::ERROR: Error converting input transform to required transform type with center.**
Any suggestions how this can be solved? Thanks!
---
### Author:  [@zivy](https://discourse.itk.org/u/zivy)
#### Post date: [December 3, 2021, 5:05pm UTC](https://discourse.itk.org/t/centeredtransforminitializer-with-only-translationtransform/4635/2 "2021-12-03T17:05:30Z")
Hello @sdbonte,
Hard to debug without the short code used here. This is possibly a display issue.
When working with 3D images highly recommended to use an external viewer. Fiji is the default in SimpleITK, ITK-SNAP highly recommended for quick image viewing, see [this notebook](https://github.com/InsightSoftwareConsortium/SimpleITK-Notebooks/blob/master/Python/04_Image_Display.ipynb) for details.
Short code snippet:
```auto
import SimpleITK as sitk
fixed_image_file = 'a.nii.gz'
moving_image_file = 'b.nii.gz'
fixed_image = sitk.ReadImage(fixed_image_file, sitk.sitkFloat32)
moving_image = sitk.ReadImage(moving_image_file, sitk.sitkFloat32)
sitk.Show(fixed_image, 'fixed')
sitk.Show(moving_image, 'moving')
initial_transform = sitk.CenteredTransformInitializer(fixed_image,
moving_image,
sitk.Euler3DTransform(),
sitk.CenteredTransformInitializerFilter.GEOMETRY
)
moving_resampled = sitk.Resample(moving_image, fixed_image, initial_transform, sitk.sitkLinear, 0.0, moving_image.GetPixelID())
sitk.Show(moving_resampled, 'moving_resampled')
```
Meaning of error message:
The `CenteredTransformInitializer` is expecting a transformation which has a `center`, `TranslationTransform` is not one of the transformations that has a center, hence the error. For additional details about transformations see [this notebook](https://github.com/InsightSoftwareConsortium/SimpleITK-Notebooks/blob/master/Python/22_Transforms.ipynb).
---
### Author:  [@ljjiayou](https://discourse.itk.org/u/ljjiayou)
#### Post date: [February 11, 2023, 1:20pm UTC](https://discourse.itk.org/t/centeredtransforminitializer-with-only-translationtransform/4635/3 "2023-02-11T13:20:10Z")
I also met this problem. Have you solved it?