[Insight-users] Addition of two DeformationFields

[Monica Lumbardi]

Hi Luis, Hi James,

Thanks a lot for your advices!!!!

Monica


--- "Miller, James V (Research)" <millerjv at crd.ge.com>
wrote:

> Monica, 
>  
> The issue with the AddImageFilter is that it relies
> on the NumericTraits
> class to define a
> type for accumulating the results.  For instance, if
> you are adding to char
> images, you would use an accumulate type of short to
> avoid overflow during
> the accumulation.
>  
> There is not specialization for
> NumericTraits<Vector<T>>.  You might try
> putting one in your code (you can use one of the
> existing specializations to
> see what traits need to be defined). But I don't
> think this will work given
> the class heirarchy for NumericTraits.
>  
> We could add another algorithm to specifically add
> two vector images.
>  
> However, looking back at your original question, it
> sounds like your two
> deformation fields are at different resolutions. So
> the smaller one would
> need to be interpolated.  You could something like
>  
> typedef
>
itk::VectorLinearInterpolateImageFunction<SmallImageType>
> VectorInterpolatorType;
>  
> VectorInterpolatorType::Pointer interpolator =
> VectorInterpolatorType::New();
> interpolator->SetInputImage( smallField );
>  
> OutputIteratorType outIt =
> OutputIteratorType(cumulativeField, region);
> LargeInputIteratorType inIt =
> LargeInputIteratorType(largeField, region);
>  
> VectorType v1, v2;
> PointType p;
> while (!inIt.IsAtEnd())
> {
>     largeField->TransfromIndexToPhysicalPoint(
> inIt.GetIndex(), p );
>     v1 = inIt.Get();
>  
>     // interpolate a vector from the smaller image
> at this physical position
> 
>     v2 = interpolator->Evaluate(p);
>  
>    // set the output vector as the sum of the two
> vectors
>     outIt.Set( v1 + v2 );
>  
>     ++inIt;
>    ++outIt;
> }
>  
> I trust that adding deformation is what you really
> want to do.  In
> particular, you are 
> looking to add two vectors at the same physical
> position.  This is what the
> above code does. If you are looking to "concatenate"
> or "compose" to vector
> fields, where you apply one vector field to a set of
> positions, then apply
> another vector field, then you use inner loop code
> that looks like 
>  
> {
>     largeField->TransfromIndexToPhysicalPoint(
> inIt.GetIndex(), p );
>     v1 = inIt.Get();
>  
>     // to compose the vector fields, apply the first
> vector field to the
> position
>     newp = p + v1;
>     
>     // interpolate the vector to compose with from
> the smaller image
>     v2 = interpolator->Evaluate(newp);
>  
>     // apply the second vector field to position
>     newp += v2;
>  
>     // composite vector is the difference between
> the original point and the
> moved point
>     outIt.Set( newp - p );
>  
>     ++inIt;
>     ++outIt;
> }
>  
> If you want, you can put in a feature request on the
> ITK bug tracker for a
> filter that will composite two vector fields.
>  
> 
> [Jim Miller] 
>  
>  
>


		
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