[ITK-users] bug in EuclideanDistancePointMetric

[Matt McCormick]

Hi Taylor, Marcel,

Yes this sounds like a bug, and the proposed solution looks good.

Please consider submitting a patch [1] that includes a new test that
does 3D-2D point set registration.

Thanks,
Matt

[1] https://insightsoftwareconsortium.github.io/ITKBarCamp-doc/CommunitySoftwareProcess/SubmitAPatchToGerrit/index.html

On Wed, Feb 4, 2015 at 2:22 PM, Taylor Braun-Jones
<taylor at braun-jones.org> wrote:
> Marcel Schenderlein <marcel.schenderlein at ...> writes:
>>
>> it seems to me as if there is a bug in itk::EuclideanDistancePointMetric
>> or at least a misconception. Correct me if I am wrong. I do not have the
>> full Insight into ITK yet
>>
>> I came across this when I wanted to use this metric together with an
>> itk::Rigid3DPerspectiveTransform and the
>> itk::PointSetToPointSetRegistrationMethod to do 3D-2D point
>> registration. The bug will not be noticed when two point sets of the
>> same dimensionality would be used.
>>
>> BUG:
>> -------
>> In the itk::EuclideanDistancePointMetric class there is a single
>> iterator type used for both FixedPointSet and MovingPointSet (typedef
>> typename Superclass::PointIterator PointIterator) in the method
>> GetValue(...) at lines 76,77
>>
>>  > PointIterator pointItr = movingPointSet->GetPoints()->Begin();
>>  > PointIterator pointEnd = movingPointSet->GetPoints()->End();
>>
>> and lines 118,119
>>
>>  > PointIterator pointItr2 = fixedPointSet->GetPoints()->Begin();
>>  > PointIterator pointEnd2 = fixedPointSet->GetPoints()->End();
>>
>> in itkEuclideanDistancePointMetric.txx. The problem that arises is that
>> if I use this metric with an itk::PointSet< double, 2 > as
>> FixedPointSetType and and itk::PointSet< double, 3 > as the
>> MovingPointSetType (as I would do for 3D-2D registration) then the
>> compiler complains about the lines 76,77 because PointIterator is
>> actually a FixedPointSetType::PointsContainer::ConstIterator (from
>> itk::PointSetToPointSetMetric). Note that the lines 118,119 work
>> perfectly but the naming of the iterator does not point to the type used.
>> I did the following to fix this:
>>
>> FIX:
>> --------------------------------
>> I introduced two new iterators (itkEuclideanDistancePointMetric.h):
>>
>>  > typedef typename FixedPointSetType::PointsContainer::ConstIterator
>> FixedPointIterator;
>>  > typedef typename MovingPointSetType::PointsContainer::ConstIterator
>> MovingPointIterator;
>>
>> The iterator PointIterator is obsolete then.
>>
>> I also had to change the distance map part of the template
>> declaration(?) (itkEuclideanDistancePointMetric.h). The dimension of the
>> distance map has to be of type TFixedPointSet instead of
>> TMovingPointSet, since the moving points are transformed (into the
>> FixedPointType) and then compared to the fixed points. So it is now:
>>
>>  > template < class TFixedPointSet, class TMovingPointSet,
>>  >  class TDistanceMap = ::itk::Image<unsigned short,
>>  >  ::itk::GetPointSetDimension<TFixedPointSet>::PointDimension> >
>>  > class ITK_EXPORT EuclideanDistancePointMetric :
>>
>> In the definition of GetValue(...) (itkEuclideanDistancePointMetric.txx)
>> I changed the lines 76,77 to
>>
>>  > MovingPointIterator pointItr = movingPointSet->GetPoints()->Begin();
>>  > MovingPointIterator pointEnd = movingPointSet->GetPoints()->End();
>>
>> and lines 118,119 to
>>
>>  > FixedPointIterator pointItr2 = fixedPointSet->GetPoints()->Begin();
>>  > FixedPointIterator pointEnd2 = fixedPointSet->GetPoints()->End();
>>
>> After that it compiles well and the registration seems to work. I have
>> not testet the fix with point sets of the same dimensionality but
>> looking at the code I see no reason why it should not still work this way.
>
>
> I'm looking at a current ITK master and see the same problem. Marcel's patch
> seems to work for me. Is it agreed that this is a bug and that Marcel's
> solution is the correct one?
>
> Thanks,
> Taylor
>
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