No subject

option.=20

1) Is this because of the itkVTKPolyDataReader or because of the ICP =
method? I tried both, with the ITK_USE_REVIEW option turned on and off. =
I did not notice a difference.

I understood, that I have to begin with a rigid and/or affine =
registration to align the point sets as good as possible before starting =
with deformable registration methods.=20

2) Is the BSplineDeformableTransform suitable at all with ICP? Are there =
alternatives?

I use the TransformPoint-function to transform a point from a PointSet.=20

3) Is the transformation, obtained by the ICP-Registration: is it true, =
that it is based on a "forward-warping" principle, which is different to =
other registration methods?

To apply the transform to a 3D-image I would have to invert the =
transform. I tried the InverseDeformationFieldImageFilter to generate an =
approximation of the inverse deformation field. I ended up varying the =
SubSamplingFactor from 100 down to lower numbers to improve the result. =
At about 10 my memory was not sufficient but the result still looked =
odd.

4) Besides varying the SubSamplingFactor, are there other ways of tuning =
this filter?

BTW: Due to lack of success with InverseDeformationFieldImageFilter, I =
am now playing with an approach suggested by Matthias (post from =
October, 15th, 2008)(map and invert the displacements for each voxel at =
the corresponding position in the moving image grid).=20

I learned, that it is a trade-off with computer-time and quality of the =
result, but:

5) What are recommended maximum numbers of points for a =
BSpline-PointSetRegistration?=20

I reduced my point clouds to about 2000 points to speed up the =
registration. I know, that to some extend it depends on the number =
coefficients to be determined, e.g. one cannot do a =
PointSet-Registration with a PointSet of 300 points and then calculate a =
BSpline-Grid (3rd order in 3D) with ((3+2)^3)*3 =3D 375 unknown =
coefficients.=20

The coefficients do not converge after 4000 iterations with the =
Levenberg-Marquardt optimizer. ("too many iterations error"). Some of =
the coefficients I got from the registration pointer, are too high. The =
should be in the the range of 0 to +/-100, while some are far beyond the =
grid-spacing, e.g. 1e3 ... 1e5.

6) Can I constrain the BSpline-Grid coefficients in order to improve or =
speed up the calculation?

Sorry for the long list of questions.

Thanks for any hints in advance!

Best regards
Lars



-----Urspr=FCngliche Nachricht-----
Von: insight-users-bounces at itk.org =
[mailto:insight-users-bounces at itk.org] Im Auftrag von Luis Ibanez
Gesendet: Sonntag, 7. Dezember 2008 00:11
An: nourmestiri at yahoo.fr
Cc: ITK
Betreff: Re: [Insight-users] Registration method


Hi Nour,


              Welcome to ITK !


Yes,
you can do PointSet registration with ITK.


Please do the following:


1) Build ITK by turning ON the ITK_USE_REVIEW (advanced) flag in CMake.


2) Use the itkVTKPolyDataReader.h class that you can find in
    Insight/Code/Review, in order to load the two polydata files
    into ITK. This will read legacy files in .vtk format.

    If you have VRML file, then convert them first to .vtk files.
    You can do this by using VTK readers and writers.


3) Use the ICP method, as described in the examples:

       Insight/Examples/Patented
          IterativeClosestPoint1.cxx
          IterativeClosestPoint2.cxx
          IterativeClosestPoint3.cxx


     Please note that the patent on the ICP method has expired,
     so you don't have to worry about it at this point.



    Regards,


       Luis


--------------------
Nour Mestiri wrote:
> Hi all ITK users,
> I'm new with you so please don't blame me if my questions are evident=20
> and try to help me if possible.
> I wanna do the registration of 2 objects (polydatas generated from =
vrml=20
> files).
> Is it possible? Is there a code example which allows to make that?
> Please i need help.
> Thank you so much
>=20
>=20
>=20
> =
------------------------------------------------------------------------
>=20
> _______________________________________________
> Insight-users mailing list
> Insight-users at itk.org
> http://www.itk.org/mailman/listinfo/insight-users
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