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/*=========================================================================
*
* 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
*
* https://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 itkBSplineDerivativeKernelFunction_h
#define itkBSplineDerivativeKernelFunction_h
#include "itkBSplineKernelFunction.h"
#include "itkMath.h"
namespace itk
{
/** \class BSplineDerivativeKernelFunction
* \brief Derivative of a BSpline kernel used for density estimation and
* nonparametric regression.
*
* This class encapsulates the derivative of a BSpline kernel for
* density estimation or nonparametric regression.
* See documentation for KernelFunctionBase for more details.
*
* This class is templated over the spline order.
* \warning Evaluate is only implemented for spline order 1 to 4
*
* \sa KernelFunctionBase
*
* \ingroup Functions
* \ingroup ITKCommon
*/
template <unsigned int VSplineOrder = 3, typename TRealValueType = double>
class ITK_TEMPLATE_EXPORT BSplineDerivativeKernelFunction : public KernelFunctionBase<TRealValueType>
{
public:
ITK_DISALLOW_COPY_AND_MOVE(BSplineDerivativeKernelFunction);
/** Standard class type aliases. */
using Self = BSplineDerivativeKernelFunction;
using Superclass = KernelFunctionBase<TRealValueType>;
using Pointer = SmartPointer<Self>;
using typename Superclass::RealType;
/** Method for creation through the object factory. */
itkNewMacro(Self);
/** \see LightObject::GetNameOfClass() */
itkOverrideGetNameOfClassMacro(BSplineDerivativeKernelFunction);
/** Enum of for spline order. */
static constexpr unsigned int SplineOrder = VSplineOrder;
/** Evaluate the function. Faster than the `Evaluate` member function, because it is static (while `Evaluate` is
* virtual). */
static TRealValueType
FastEvaluate(const TRealValueType u)
{
return Self::Evaluate(Dispatch<VSplineOrder>(), u);
}
/** Evaluate the function. */
TRealValueType
Evaluate(const TRealValueType & u) const override
{
return Self::FastEvaluate(u);
}
protected:
BSplineDerivativeKernelFunction() = default;
~BSplineDerivativeKernelFunction() override = default;
void
PrintSelf(std::ostream & os, Indent indent) const override
{
Superclass::PrintSelf(os, indent);
os << indent << "Spline Order: " << SplineOrder << std::endl;
}
private:
/** Structures to control overloaded versions of Evaluate */
struct DispatchBase
{};
template <unsigned int>
struct Dispatch : public DispatchBase
{};
/** Evaluate the function: zeroth order spline. */
inline static TRealValueType
Evaluate(const Dispatch<0> &, const TRealValueType & itkNotUsed(u))
{
return TRealValueType{ 0.0 };
}
/** Evaluate the function: first order spline */
inline static TRealValueType
Evaluate(const Dispatch<1> &, const TRealValueType & u)
{
if (Math::ExactlyEquals(u, TRealValueType{ -1.0 }))
{
return TRealValueType{ 0.5 };
}
else if ((u > TRealValueType{ -1.0 }) && (u < TRealValueType{ 0.0 }))
{
return TRealValueType{ 1.0 };
}
else if (Math::ExactlyEquals(u, TRealValueType{ 0.0 }))
{
return TRealValueType{ 0.0 };
}
else if ((u > TRealValueType{ 0.0 }) && (u < TRealValueType{ 1.0 }))
{
return TRealValueType{ -1.0 };
}
else if (Math::ExactlyEquals(u, TRealValueType{ 1.0 }))
{
return TRealValueType{ -0.5 };
}
else
{
return TRealValueType{ 0.0 };
}
}
/** Evaluate the function: second order spline. */
inline static TRealValueType
Evaluate(const Dispatch<2> &, const TRealValueType & u)
{
if ((u > TRealValueType{ -0.5 }) && (u < TRealValueType{ 0.5 }))
{
return (TRealValueType{ -2.0 } * u);
}
else if ((u >= TRealValueType{ 0.5 }) && (u < TRealValueType{ 1.5 }))
{
return (TRealValueType{ -1.5 } + u);
}
else if ((u > TRealValueType{ -1.5 }) && (u <= TRealValueType{ -0.5 }))
{
return (TRealValueType{ 1.5 } + u);
}
else
{
return TRealValueType{ 0.0 };
}
}
/** Evaluate the function: third order spline. */
inline static TRealValueType
Evaluate(const Dispatch<3> &, const TRealValueType & u)
{
if ((u >= TRealValueType{ 0.0 }) && (u < TRealValueType{ 1.0 }))
{
return (TRealValueType{ -2.0 } * u + TRealValueType{ 1.5 } * u * u);
}
else if ((u > TRealValueType{ -1.0 }) && (u < TRealValueType{ 0.0 }))
{
return (TRealValueType{ -2.0 } * u - TRealValueType{ 1.5 } * u * u);
}
else if ((u >= TRealValueType{ 1.0 }) && (u < TRealValueType{ 2.0 }))
{
return (TRealValueType{ -2.0 } + TRealValueType{ 2.0 } * u - TRealValueType{ 0.5 } * u * u);
}
else if ((u > TRealValueType{ -2.0 }) && (u <= TRealValueType{ -1.0 }))
{
return (TRealValueType{ 2.0 } + TRealValueType{ 2.0 } * u + TRealValueType{ 0.5 } * u * u);
}
else
{
return TRealValueType{ 0.0 };
}
}
/** Evaluate the function: unimplemented spline order */
inline static TRealValueType
Evaluate(const DispatchBase &, const TRealValueType &)
{
itkGenericExceptionMacro("Evaluate not implemented for spline order " << SplineOrder);
}
};
} // end namespace itk
#endif
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