[ITK-users] Question about LandmarkDisplacementFieldSource

[Siming Bayer]

Hi Matt,

Thank you for the information.

Since I would like to perform non-rigid image registration, I would like to first compute a displacement field using 2 point set and then deform the image with the displacement field. So LandmarkBasedTransformInitializer is not suitable in my case. 


Basically, I extract two point sets from images of vessels (one before non-rigid deformation, one after deformation). Those two point sets are then aligned by using TPS-RPM Algorithm by Chui. For my understanding, the output displacement field from LandmarkDisplacementFieldSource should be the perfect deformation field, with which I can warp the input vessel image with WarpImageFilter. According to the documentation and the code of LandmarkDisplacementFieldSource, it also use Kernel Based Spline (TPS as default) to compute the deformation field from two point sets. But now, the resulting displacement field is quite strange, although the point matching algorithm works fine. I simple have no idea why my implementation produce wrong output displacement field.

So I think, I need to deepen into the details of the KernelTransform implementation. 

best,
Siming

> Am 29.08.2017 um 21:26 schrieb Matt McCormick <matt.mccormick at kitware.com>:
> 
> Hi Siming,
> 
> To find the references, see the documentation for the KernelSplines:
> 
>  https://itk.org/Doxygen/html/classitk_1_1KernelTransform.html
> 
> The Inheritance Diagram has links to specific splines and they also
> have references.
> 
> 
> If dealing with two point sets, you may also be interested in the
> LandmarkBasedTransformInitializer:
> 
>  https://itk.org/Doxygen/html/classitk_1_1LandmarkBasedTransformInitializer.html
> 
> 
> Hope this helps,
> Matt
> 
> 
> 
> On Tue, Aug 29, 2017 at 12:09 PM, Siming Bayer <siming.bayer at gmail.com> wrote:
>> Dear all,
>> 
>> I am trying to use LandmarkDisplacementFieldSource to compute a displacement
>> field from 2 point sets. Although the 2 point sets are aligned almost
>> perfectly with thin plate spline - Robust point matching algorithm
>> (TPS-RPM), the resulting displacement field looks simply wrong. For example,
>> the displacement field has a high value where I don´t expect any
>> deformation/displacement.
>> 
>> Does anybody knows the mathematical background of the itk implementation of
>> LandmarkDisplacementFieldSource? Could anybody tell me the paper? Does any
>> body knows how many landmarks is meaningful?
>> 
>> best,
>> Siming
>> 
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