[Insight-users] ICP Registration

[zhixi]

Hi Luis,

Thanks for your quick reply.  I've tried to do more ICP, but it seems like
the method is giving me incorrect transform parameters.  To test the method,
I made two point sets of 111 points each, basically identical objects
shifted off in the z direction by 1 voxel (they overlap).  The ICP
registration should give me something like [0, 0, 0, 0, 0, 1]

instead I'm getting this:[-2.7e-9, -9.7e-10, 0.26, 0.27, .55]

these parameters are clearly wrong.  Also, If I make the two objects be
offset such that they do not overlap, the ICP registration gives me 0's for
the parameters.  Is this method only useful for overlapping objects? or are
there other settings within the code itself that I can tweak to search a
wider area?
I ask because my project involves rigidly registering organs from different
patients.  ICP makes sense for my situation, but if it cannot register
organs that do not overlap in space, then it doesn't do me any good.

Also, Please if you could, explain the convergence criteria in the ICP ex.
2:

double          gradientTolerance  =  1e-4;   // convergence criterion
  double          valueTolerance     =  1e-4;   // convergence criterion
  double          epsilonFunction    =  1e-5;   // convergence criterion

what do each of these mean?  After playing with different combinations,
going high and low, varying one at at time, etc, it seems like the
epsilonFunction is the variable that has the most impact on results.   

however, I have not seen a transform parameter after all my tinkering that
actually looks right.
Thank you so much for any insight you can provide.

yours,

Zhixi Li 
 















Luis Ibanez wrote:
> 
> 
> Hi Zhixi,
> 
> Yes, you can simply use the transform parameter to initialize
> the Transform that you will give to the ResampleImageFilter.
> 
> Note that you should copy also the Center of rotation of the
> transform, but since here you are planning to reuse the transform
> object that you employed for the point-based registration, the two
> lines that you suggested should do the trick:
> 
> 
>    finalTransform->SetParameters( transform->GetParameters() );
>    resample->SetTransform( finalTransform );
> 
> 
> Please let us know if you find any problems,
> 
> 
>    Thanks,
> 
> 
>       Luis
> 
> 
> -----------------
> zhixi wrote:
>> Hello,
>> 
>> I am trying to do a rigid registration of two 3D images with ICP. 
>> Following
>> the ICP ex. 2 in the patented examples folder,  I extracted the surface
>> points of the two images and passed them into the moving and fixed point
>> containers.  Then, using the euler 3d transform and LevenbergMarquatd
>> optimizer, the ICP algorithm seems to give me 6 parameters for the final
>> transform in an array form.
>> 
>> my problem is now the actual resampling of the images.  
>> 
>> my specific question is, can I simply pass the transform parameters into
>> the
>> resampler?  Will it know what to do with them?
>> 
>> i.e., with this pathway, where transform->GetParameters() gets me the
>> transfrom from the ICP.
>> 
>> 
>> finalTransform->SetParameters( transform->GetParameters() );
>> 
>> resample->SetTransform( finalTransform );
>> 
>> 
>> 
>> 
>> 
>> here is my resampling code:
>> 
>> 	typedef itk::Image< float, 3 >   ImageType_3D;
>> 	ImageType_3D::Pointer ITKim_3D1 = ImageType_3D::New();
>> 	ImageType_3D::Pointer ITKim_3D2 = ImageType_3D::New();
>> 
>> 	Copy_CISImage_to_ITKImage(img3Din1, ITKim_3D1);
>> 	Copy_CISImage_to_ITKImage(img3Din2, ITKim_3D2);
>> 	typedef itk:: NearestNeighborInterpolateImageFunction <ImageType_3D ,
>> double> InterpolatorType;
>> 	InterpolatorType::Pointer interpolator = InterpolatorType::New();
>> 
>> 
>>   typedef itk::ResampleImageFilter< ImageType_3D, ImageType_3D >   
>> ResampleFilterType;
>>   TransformType::Pointer finalTransform = TransformType::New();
>>   
>>   finalTransform->SetParameters( transform->GetParameters() );
>> 
>>   ResampleFilterType::Pointer resample = ResampleFilterType::New();
>>   resample->SetTransform( finalTransform );
>>   resample->SetInput( ITKim_3D2);
>>   resample->SetSize( ITKim_3D1->GetLargestPossibleRegion().GetSize() );
>>   resample->SetOutputOrigin(  ITKim_3D1->GetOrigin() );
>>   resample->SetOutputSpacing( ITKim_3D1->GetSpacing() );
>>   resample->SetDefaultPixelValue( 1 );
>>   resample->SetInterpolator( interpolator );
>> 
>> 	resample->Update();
>>   Copy_ITKImage_to_CISImage(resample->GetOutput(), img3Dout );
>> 
>> 
>> 
>> }
>> 
>> 
>> Any help is greatly appreciated,
>> 
>> Zhixi Li
> _______________________________________________
> Insight-users mailing list
> Insight-users at itk.org
> http://www.itk.org/mailman/listinfo/insight-users
> 
> 

-- 
View this message in context: http://www.nabble.com/ICP-Registration-tf4251126.html#a12135215
Sent from the ITK - Users mailing list archive at Nabble.com.