itkBSplineKernelFunction.h

Go to the documentation of this file.

/*=========================================================================
 *
 *  Copyright NumFOCUS
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/
#ifndef itkBSplineKernelFunction_h
#define itkBSplineKernelFunction_h
 
#include "itkKernelFunctionBase.h"
#include "itkMath.h"
 
namespace itk
{
template <unsigned int VSplineOrder = 3, typename TRealValueType = double>
class ITK_TEMPLATE_EXPORT BSplineKernelFunction : public KernelFunctionBase<TRealValueType>
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(BSplineKernelFunction);
 
  using Self = BSplineKernelFunction;
  using Superclass = KernelFunctionBase<TRealValueType>;
  using Pointer = SmartPointer<Self>;
 
  using RealType = typename Superclass::RealType;
  itkNewMacro(Self);
 
  itkTypeMacro(BSplineKernelFunction, KernelFunctionBase);
 
  static constexpr unsigned int SplineOrder = VSplineOrder;
 
  TRealValueType
  Evaluate(const TRealValueType & u) const override
  {
    return this->Evaluate(Dispatch<VSplineOrder>(), u);
  }
 
protected:
  BSplineKernelFunction() = default;
  ~BSplineKernelFunction() override = default;
  void
  PrintSelf(std::ostream & os, Indent indent) const override
  {
    Superclass::PrintSelf(os, indent);
    os << indent << "Spline Order: " << SplineOrder << std::endl;
  }
 
private:
  struct DispatchBase
  {};
  template <unsigned int>
  struct Dispatch : public DispatchBase
  {};
 
  inline TRealValueType
  Evaluate(const Dispatch<0> &, const TRealValueType & u) const
  {
    const TRealValueType absValue = itk::Math::abs(u);
    if (absValue < static_cast<TRealValueType>(0.5))
    {
      return NumericTraits<TRealValueType>::OneValue();
    }
    else if (Math::ExactlyEquals(absValue, static_cast<TRealValueType>(0.5)))
    {
      return static_cast<TRealValueType>(0.5);
    }
    else
    {
      return NumericTraits<TRealValueType>::ZeroValue();
    }
  }
 
  inline TRealValueType
  Evaluate(const Dispatch<1> &, const TRealValueType & u) const
  {
    const TRealValueType absValue = itk::Math::abs(u);
    if (absValue < NumericTraits<TRealValueType>::OneValue())
    {
      return NumericTraits<TRealValueType>::OneValue() - absValue;
    }
    else
    {
      return NumericTraits<TRealValueType>::ZeroValue();
    }
  }
 
  inline TRealValueType
  Evaluate(const Dispatch<2> &, const TRealValueType & u) const
  {
    const TRealValueType absValue = itk::Math::abs(u);
    if (absValue < static_cast<TRealValueType>(0.5))
    {
      const TRealValueType sqrValue = itk::Math::sqr(absValue);
      return static_cast<TRealValueType>(0.75) - sqrValue;
    }
    else if (absValue < static_cast<TRealValueType>(1.5))
    {
      const TRealValueType sqrValue = itk::Math::sqr(absValue);
      // NOTE: 1.0/8.0 == static_cast< TRealValueType >( 0.125 )
      return (static_cast<TRealValueType>(9.0) - static_cast<TRealValueType>(12.0) * absValue +
              static_cast<TRealValueType>(4.0) * sqrValue) *
             static_cast<TRealValueType>(0.125);
    }
    else
    {
      return NumericTraits<TRealValueType>::ZeroValue();
    }
  }
 
  inline TRealValueType
  Evaluate(const Dispatch<3> &, const TRealValueType & u) const
  {
    const TRealValueType absValue = itk::Math::abs(u);
    if (absValue < NumericTraits<TRealValueType>::OneValue())
    {
      const TRealValueType sqrValue = itk::Math::sqr(absValue);
      return (static_cast<TRealValueType>(4.0) - static_cast<TRealValueType>(6.0) * sqrValue +
              static_cast<TRealValueType>(3.0) * sqrValue * absValue) /
             static_cast<TRealValueType>(6.0);
    }
    else if (absValue < static_cast<TRealValueType>(2.0))
    {
      const TRealValueType sqrValue = itk::Math::sqr(absValue);
      return (static_cast<TRealValueType>(8.0) - static_cast<TRealValueType>(12.0) * absValue +
              static_cast<TRealValueType>(6.0) * sqrValue - sqrValue * absValue) /
             static_cast<TRealValueType>(6.0);
    }
    else
    {
      return NumericTraits<TRealValueType>::ZeroValue();
    }
  }
 
  inline TRealValueType
  Evaluate(const DispatchBase &, const TRealValueType &) const
  {
    itkExceptionMacro("Evaluate not implemented for spline order " << SplineOrder);
  }
};
} // end namespace itk
 
#endif