itkGaussianKernelFunction.h

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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 itkGaussianKernelFunction_h
#define itkGaussianKernelFunction_h
 
#include "itkKernelFunctionBase.h"
#include "itkMath.h"
#include <cmath>
 
namespace itk
{
template <typename TRealValueType = double>
class ITK_TEMPLATE_EXPORT GaussianKernelFunction : public KernelFunctionBase<TRealValueType>
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(GaussianKernelFunction);

  using Self = GaussianKernelFunction;
  using Superclass = KernelFunctionBase<TRealValueType>;
  using Pointer = SmartPointer<Self>;
 
  using typename Superclass::RealType;
  itkNewMacro(Self);

  itkOverrideGetNameOfClassMacro(GaussianKernelFunction);

  TRealValueType
  Evaluate(const TRealValueType & u) const override
  {
    constexpr auto negHalf = TRealValueType{ -0.5 };
    return std::exp(negHalf * itk::Math::sqr(u)) * Math::one_over_sqrt2pi;
  }

 
protected:
  GaussianKernelFunction() {}
  ~GaussianKernelFunction() override = default;
  void
  PrintSelf(std::ostream & os, Indent indent) const override
  {
    Superclass::PrintSelf(os, indent);
  }
};
} // end namespace itk
 
#endif