[Insight-users] Question regarding BSplineScatteredDataPointSetToImageFilter

[Nicholas Tustison]

Hi Kerstin,

You're not setting your point locations in the parametric domain.
Inside your loop where you're setting the point data, you also need
to store the parametric location of your points inside your domain,i.e.

pointSet->SetPointData(num, v)

PointSetType::PointType point;

point[0] = x;
point[1] = y;
point[2] = z; 
point[3] = t;

pointSet->SetPoint( num, point );
num++

where x, y, z, and t describes the parametric location of your data
point.

A couple other things you might want to consider.  

1. The BSpline filter has been in ITK proper for some time
now and I know I've made several changes (including a
thorough parallelization for significant speed-up) since then.
You might want to consider using the class that's in ITK 
already.

2. 67 control points is quite a bit.  That, coupled with 5 levels,
would mean you would end up with a control point lattice of
(6-3) * 2^(5-1) x (6-3) * 2^(5-1) x (6-3) * 2^(5-1) x (67-3) * 2^(5-1) =
48x48x48x1024.  A large lattice size in the temporal dimension 
might not be necessary.

Nick 


On Dec 23, 2011, at 4:19 AM, Kerstin Müller wrote:

> Hi,
> 
> I'm using the BSplineScatteredDataPointSetToImageFilter from the Insight Journal. However,
> I cannot find the correct parameter in order to make the filter work and does not crash during the evaluation.
> I'll have scattered 3-D points over time and I want to fit a 4-D Bspline field to that points. Afterwards I want to evaluate the Bspline on a dense volume grid to one time step.
> 
> Here you can find the code, unfortunately it crashes (either due to memory problems or without any error output)
> 
> 
> const unsigned int ParametricDimension = 4;
>     const unsigned int DataDimension = 3;
> 
>     typedef double RealType;
>     typedef itk ::Vector <RealType , DataDimension > VectorType;
>     typedef itk ::Image <VectorType , ParametricDimension > ImageType;
> 
>     typedef itk :: PointSet <VectorType , ParametricDimension > PointSetType ;
>     PointSetType :: Pointer pointSet = PointSetType :: New ();
>     
>     // Set the sample points
>     for ( int img_num = 0; img_num < m_configuration.num_projections ; img_num++ ) 
>     {
>         int num = 0;
>         for( int idx = 0; idx <= points.at(img_num).size()-3; idx+=3 )
>         {
>             
>             VectorType v;
>             v[0] = points.at(img_num)[idx];
>             v[1] = points.at(img_num)[idx+1];
>             v[2] = points.at(img_num)[idx+2];
>             pointSet->SetPointData(num, v);
> 
>             num++;
> 
>         }
>     }
>     // Instantiate the filter and set the parameters
>     typedef itk::myBSplineScatteredDataPointSetToImageFilter<PointSetType , ImageType > FilterType;
>     FilterType :: Pointer filter = FilterType :: New ();
> 
>     // Define the parametric domain
>     ImageType :: SpacingType spacing; 
>     spacing[0] = 42.0f;
>     spacing[1] = 42.0f;
>     spacing[2] = 42.0f;
>     spacing[3] = 2.0f;
>     ImageType :: SizeType size; 
>     size[0] = 6;
>     size[1] = 6;
>     size[2] = 6;
>     size[3] = 67;
>     ImageType :: PointType origin; 
>     origin.Fill( 0.0 );
> 
>     filter ->SetSize( size );
>     filter ->SetOrigin( origin );
>     filter ->SetSpacing( spacing );
>     filter ->SetInput( pointSet );
> 
>     filter -> SetSplineOrder ( 3 );
>     FilterType :: ArrayType ncps;
>     ncps.SetElement(0,6);
>     ncps.SetElement(1,6);
>     ncps.SetElement(2,6);
>     ncps.SetElement(3,67);
> 
>     filter -> SetNumberOfControlPoints ( ncps );
>     filter -> SetNumberOfLevels ( 5 );
>     filter -> SetGenerateOutputImage ( false );
> 
>     try
>     {
>         filter ->Update ();
>     }
>     catch ( itk::ExceptionObject & excp )
>     {
>         std :: cerr << "Test 2: itkBSplineScatteredDataImageFilter exception thrown" << std:: endl;
>         std::cerr<< excp <<std::endl;
>     }
> 
> Thank you for your help!
> 
> Best,
> 
> Kerstin
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