text: /*=========================================================================
   *
   *  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 itkCollidingFrontsImageFilter_h
  #define itkCollidingFrontsImageFilter_h
  
  #include "itkFastMarchingUpwindGradientImageFilter.h"
  #include "itkImageToImageFilter.h"
  
  namespace itk
  {
  /** \class CollidingFrontsImageFilter
   *
   * \brief Selects a region of space where two independent fronts run towards
   * each other.
   *
   * The filter can be used to quickly segment anatomical structures (e.g. for
   * level set initialization).
   *
   * The filter uses two instances of FastMarchingUpwindGradientImageFilter to
   * compute the gradients of arrival times of two wavefronts propagating from
   * two sets of seeds. The input of the filter  is used as the speed of the two
   * wavefronts. The output is the dot product between the two gradient vector
   * fields.
   *
   * The filter works on the following basic idea. In the regions where the dot
   * product between the two gradient fields is negative, the two fronts
   * propagate in opposite directions. In the regions where the dot product is
   * positive, the two fronts propagate in the same direction.  This can be used
   * to extract the region of space between two sets of points.
   *
   * If StopOnTargets is On, then each front will stop as soon as all seeds of
   * the other front have been reached. This can markedly speed up the execution
   * of the filter, since wave propagation does not take place on the complete
   * image.
   *
   * Optionally, a connectivity criterion can be applied to the resulting dot
   * product image. In this case, the only negative region in the output image is
   * the one connected to the seeds.
   *
   * \author Luca Antiga Ph.D.  Biomedical Technologies Laboratory,
   *                            Bioengineering Department, Mario Negri Institute, Italy.
   *
   * \ingroup ITKLevelSets
   */
  template <typename TInputImage, typename TOutputImage>
  class ITK_TEMPLATE_EXPORT CollidingFrontsImageFilter : public ImageToImageFilter<TInputImage, TOutputImage>
  {
  public:
    ITK_DISALLOW_COPY_AND_MOVE(CollidingFrontsImageFilter);
  
    /** Standard class type aliases. */
    using Self = CollidingFrontsImageFilter;
    using Superclass = ImageToImageFilter<TInputImage, TOutputImage>;
    using Pointer = SmartPointer<Self>;
    using ConstPointer = SmartPointer<const Self>;
  
    /** Method for creation through the object factory. */
    itkNewMacro(Self);
  
    /** Run-time type information (and related methods) */
    itkTypeMacro(CollidingFrontsImageFilter, ImageToImageFilter);
  
    /** Extract some information from the image types.  Dimensionality
     * of the two images is assumed to be the same. */
    using OutputPixelType = typename TOutputImage::PixelType;
    using InputPixelType = typename TInputImage::PixelType;
    using RealType = typename NumericTraits<InputPixelType>::RealType;
  
    /** Extract some information from the image types.  Dimensionality
     * of the two images is assumed to be the same. */
    static constexpr unsigned int ImageDimension = TOutputImage::ImageDimension;
  
    /** Image type alias support */
    using InputImageType = TInputImage;
    using SpeedImageType = TInputImage;
    using InputImagePointer = typename InputImageType::Pointer;
    using OutputImageType = TOutputImage;
    using LevelSetImageType = TOutputImage;
    using OutputImagePointer = typename OutputImageType::Pointer;
  
    /** Superclass type alias. */
    using typename Superclass::OutputImageRegionType;
  
    /** FastMarchingUpwindGradientImageFilter type alias. */
    using FastMarchingUpwindGradientImageFilterType =
      itk::FastMarchingUpwindGradientImageFilter<LevelSetImageType, SpeedImageType>;
  
    /** Typedef support of level set method types. */
    using PixelType = typename FastMarchingUpwindGradientImageFilterType::PixelType;
    using NodeType = typename FastMarchingUpwindGradientImageFilterType::NodeType;
    using NodeContainer = typename FastMarchingUpwindGradientImageFilterType::NodeContainer;
    using NodeContainerPointer = typename FastMarchingUpwindGradientImageFilterType::NodeContainerPointer;
    using GradientImageType = typename FastMarchingUpwindGradientImageFilterType::GradientImageType;
    using IndexType = typename FastMarchingUpwindGradientImageFilterType::IndexType;
  
    /** Set the container of Seed Points representing the first initial front.
     * Seed points are represented as a VectorContainer of LevelSetNodes. */
    void
    SetSeedPoints1(NodeContainer * points)
    {
      m_SeedPoints1 = points;
      this->Modified();
    }
  
    /** Get the container of Seed Points representing the first initial front. */
    NodeContainerPointer
    GetSeedPoints1()
    {
      return m_SeedPoints1;
    }
  
    /** Set the container of Seed Points representing the second initial front.
     * Seed points are represented as a VectorContainer of LevelSetNodes. */
    void
    SetSeedPoints2(NodeContainer * points)
    {
      m_SeedPoints2 = points;
      this->Modified();
    }
  
    /** Get the container of Seed Points representing the second initial front. */
    NodeContainerPointer
    GetSeedPoints2()
    {
      return m_SeedPoints2;
    }
  
    itkSetMacro(NegativeEpsilon, double);
    itkGetConstMacro(NegativeEpsilon, double);
  
    itkSetMacro(ApplyConnectivity, bool);
    itkGetConstMacro(ApplyConnectivity, bool);
    itkBooleanMacro(ApplyConnectivity);
  
    itkSetMacro(StopOnTargets, bool);
    itkGetConstMacro(StopOnTargets, bool);
    itkBooleanMacro(StopOnTargets);
  
  #ifdef ITK_USE_CONCEPT_CHECKING
    // Begin concept checking
    itkConceptMacro(InputHasNumericTraitsCheck, (Concept::HasNumericTraits<InputPixelType>));
    // End concept checking
  #endif
  
  protected:
    CollidingFrontsImageFilter();
    ~CollidingFrontsImageFilter() override = default;
  
    void
    GenerateData() override;
  
    void
    PrintSelf(std::ostream &, Indent) const override;
  
  private:
    NodeContainerPointer m_SeedPoints1;
    NodeContainerPointer m_SeedPoints2;
  
    bool m_StopOnTargets;
    bool m_ApplyConnectivity;
  
    double m_NegativeEpsilon;
  };
  } // end namespace itk
  
  #ifndef ITK_MANUAL_INSTANTIATION
  #  include "itkCollidingFrontsImageFilter.hxx"
  #endif
  
  #endif
  