# Interpolate Bspline Transformation
**URL:** https://discourse.itk.org/t/interpolate-bspline-transformation/4214
**Category:** Algorithms
**Tags:** registration, python
**Created:** [June 16, 2021, 6:30pm UTC](https://discourse.itk.org/t/interpolate-bspline-transformation/4214 "2021-06-16T18:30:58Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Mikhail](https://discourse.itk.org/u/Mikhail)
#### Post date: [June 16, 2021, 6:30pm UTC](https://discourse.itk.org/t/interpolate-bspline-transformation/4214/1 "2021-06-16T18:30:58Z")
I have images of same object at t0 and t1. I have a bspline transformation that can be used to obtain the image at t1 from the image at t0. I would like to obtain an image at t0 \< tx \< t1. Is there a way to modify the bspline transformation to do that?
It is very simple if the transformation is the same for all voxels, such as a combination of rotation and translation. But I don’t see how to do this when all voxels are transformed differently.
I appreacite your help!
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### Author:  [@zivy](https://discourse.itk.org/u/zivy)
#### Post date: [June 16, 2021, 6:54pm UTC](https://discourse.itk.org/t/interpolate-bspline-transformation/4214/2 "2021-06-16T18:54:46Z")
Hello @Mikhail,
Not sure if you are working in ITK or SimpleITK, so rough pseudocode which is relevant for both:
1. t\_x = 0.2 # some value in [0,1].
2. `original_displacement = sitk.TransformToDisplacementField(original_bspline_transformation)`.
3. `intermidiate_displacement_field = sitk.DisplacementFieldTransform(t_x* original_displacement.GetDisplacementField())`
This is simple and problematic. The problem is that we are assuming that all points are moving at a constant velocity between times t0 and t1 (they are moving at different speeds). Unless you are really lucky this will not be the case for your data where regions accelerate/decelerate between t0, t1.
That being said, all our computations are approximations of a continuous world, so this approach may just be good enough for your needs.
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### Author:  [@Mikhail](https://discourse.itk.org/u/Mikhail)
#### Post date: [June 17, 2021, 8:43am UTC](https://discourse.itk.org/t/interpolate-bspline-transformation/4214/3 "2021-06-17T08:43:51Z")
Dear @zivy,
your solution is what I was looking for. Thanks!