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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 itkObjectToObjectMetric_h
#define itkObjectToObjectMetric_h


#include "itkObjectToObjectMetricBase.h"

#include "itkDisplacementFieldTransform.h"
#include "itkImage.h"
#include "itkObject.h"
#include "itkPointSet.h"
#include "itkTransform.h"

namespace itk
{

/**
 * \class ObjectToObjectMetric
 * \brief Computes similarity between regions of two objects.
 *
 * This class is templated over the dimensionality of the two input objects.
 * This is the abstract templated base class for a hierarchy of similarity metrics
 * that may, in derived classes, operate on meshes, images, etc.
 * This class computes a value that measures the similarity between the two
 * objects.
 *
 * Derived classes must provide implementations for:
 *  GetValue
 *  GetDerivative
 *  GetValueAndDerivative
 *  SupportsArbitraryVirtualDomainSamples
 *
 * Similarity is evaluated using fixed and moving transforms.
 * Both transforms are initialized to an IdentityTransform, and can be
 * set by the user using SetFixedTransform() and SetMovingTransform().
 *
 * Virtual Domain
 *
 * This class uses a virtual reference space. This space defines the resolution
 * at which the evaluation is performed, as well as the physical coordinate
 * system. This is useful for unbiased registration. The virtual domain is stored
 * in the m_VirtualDomain member, but this is subject to change so the convenience
 * methods GetVirtualSpacing(), GetVirtualDirection() and GetVirtualOrigin() should
 * be used whenever possible to retrieve virtual domain information. The region over which
 * metric evaluation is performed is taken from the virtual image buffered region.
 *
 * The user can define a virtual domain by calling either
 * \c SetVirtualDomain or \c SetVirtualDomainFromImage. See these
 * methods for details. Derived classes may automatically assign a virtual domain
 * if the user has not assigned one by initialization time.
 *
 * If the virtual domain is left undefined by the user and by derived classes,
 * then unit or zero values are returned for GetVirtualSpacing(),
 * GetVirtualDirection() and GetVirtualOrigin(), as appropriate. The virtual region is left
 * undefined and an attempt to retrieve it via GetVirtualRegion() will generate an exception.
 * The m_VirtualImage member will be nullptr.
 *
 * During evaluation, derived classes should verify that points are within the virtual domain
 * and thus valid, as appropriate for the needs of the metric. When points are deemed invalid
 * the number of valid points returned by GetNumberOfValidPoints() should reflect this.
 *
 * \note Transform Optimization
 * This hierarchy currently assumes only the moving transform is 'active',
 * i.e. only the moving transform is being optimized when used in an optimizer.
 * Methods relevant to transform optimization such as GetNumberOfParameters(),
 * UpdateTransformParameters() are passed on to the active transform.
 * The eventual goal however is to allow for either moving, fixed or both
 * transforms to be active within a single metric.
 *
 * \ingroup ITKOptimizersv4
 */
template <unsigned int TFixedDimension,
          unsigned int TMovingDimension,
          typename TVirtualImage = Image<double, TFixedDimension>,
          typename TParametersValueType = double>
class ITK_TEMPLATE_EXPORT ObjectToObjectMetric : public ObjectToObjectMetricBaseTemplate<TParametersValueType>
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(ObjectToObjectMetric);

  /** Standard class type aliases. */
  using Self = ObjectToObjectMetric;
  using Superclass = ObjectToObjectMetricBaseTemplate<TParametersValueType>;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

  /** \see LightObject::GetNameOfClass() */
  itkOverrideGetNameOfClassMacro(ObjectToObjectMetric);

  /** Type used for representing object components  */
  using CoordinateRepresentationType = TParametersValueType;

  /** Type for internal computations */
  using InternalComputationValueType = TParametersValueType;

  /**  Type of the measure. */
  using typename Superclass::MeasureType;

  /**  Type of object. */
  using ObjectType = typename Superclass::Object;

  /**  Type of the derivative. */
  using typename Superclass::DerivativeType;
  using typename Superclass::DerivativeValueType;

  /**  Type of the parameters. */
  using typename Superclass::ParametersType;
  using typename Superclass::NumberOfParametersType;

  using typename Superclass::GradientSourceEnum;

  /** Dimension type */
  using DimensionType = SizeValueType;

  /** Object dimension accessors */
  static constexpr DimensionType FixedDimension = TFixedDimension;
  static constexpr DimensionType MovingDimension = TMovingDimension;
  static constexpr DimensionType VirtualDimension = TVirtualImage::ImageDimension;

  /** Types for the virtual domain */
  using VirtualImageType = TVirtualImage;
  using VirtualImagePointer = typename VirtualImageType::Pointer;
  using VirtualImageConstPointer = typename VirtualImageType::ConstPointer;
  using VirtualPixelType = typename VirtualImageType::PixelType;
  using VirtualRegionType = typename VirtualImageType::RegionType;
  using VirtualSizeType = typename VirtualRegionType::SizeType;
  using VirtualSpacingType = typename VirtualImageType::SpacingType;
  using VirtualOriginType = typename VirtualImageType::PointType;
  using VirtualPointType = typename VirtualImageType::PointType;
  using VirtualDirectionType = typename VirtualImageType::DirectionType;
  using VirtualRadiusType = typename VirtualImageType::SizeType;
  using VirtualIndexType = typename VirtualImageType::IndexType;

  /** Point set in the virtual domain */
  using VirtualPointSetType = PointSet<VirtualPixelType, Self::VirtualDimension>;
  using VirtualPointSetPointer = typename VirtualPointSetType::Pointer;

  /**  Type of the Transform Base classes */
  using MovingTransformType = Transform<TParametersValueType, TVirtualImage::ImageDimension, TMovingDimension>;
  using FixedTransformType = Transform<TParametersValueType, TVirtualImage::ImageDimension, TFixedDimension>;

  using FixedTransformPointer = typename FixedTransformType::Pointer;
  using FixedInputPointType = typename FixedTransformType::InputPointType;
  using FixedOutputPointType = typename FixedTransformType::OutputPointType;
  using FixedTransformParametersType = typename FixedTransformType::ParametersType;

  using MovingTransformPointer = typename MovingTransformType::Pointer;
  using MovingInputPointType = typename MovingTransformType::InputPointType;
  using MovingOutputPointType = typename MovingTransformType::OutputPointType;
  using MovingTransformParametersType = typename MovingTransformType::ParametersType;

  /** Jacobian type. This is the same for all transforms */
  using JacobianType = typename FixedTransformType::JacobianType;
  using FixedTransformJacobianType = typename FixedTransformType::JacobianType;
  using MovingTransformJacobianType = typename MovingTransformType::JacobianType;

  /** DisplacementFieldTransform types for working with local-support transforms */
  using MovingDisplacementFieldTransformType =
    DisplacementFieldTransform<CoordinateRepresentationType, Self::MovingDimension>;

  void
  Initialize() override;

  NumberOfParametersType
  GetNumberOfParameters() const override;
  NumberOfParametersType
  GetNumberOfLocalParameters() const override;
  void
  SetParameters(ParametersType & params) override;
  const ParametersType &
  GetParameters() const override;
  bool
  HasLocalSupport() const override;
  void
  UpdateTransformParameters(const DerivativeType & derivative, TParametersValueType factor) override;

  /** Connect the fixed transform. */
  itkSetObjectMacro(FixedTransform, FixedTransformType);

  /** Get a pointer to the fixed transform.  */
  itkGetModifiableObjectMacro(FixedTransform, FixedTransformType);

  /** Connect the moving transform. */
  itkSetObjectMacro(MovingTransform, MovingTransformType);

  /** Get a pointer to the moving transform.  */
  itkGetModifiableObjectMacro(MovingTransform, MovingTransformType);

  /** Connect the moving transform using a backwards-compatible name.
   * This assigns the input transform to the moving transform. */
  void
  SetTransform(MovingTransformType * transform);

  /** Get the moving transform using a backwards-compatible name */
  const MovingTransformType *
  GetTransform();

  /** Get the number of valid points after a call to evaluate the
   * metric. */
  itkGetConstMacro(NumberOfValidPoints, SizeValueType);

  /** Define the virtual reference space. This space defines the resolution
   * at which the registration is performed as well as the physical coordinate
   * system.  Useful for unbiased registration.
   * This method will allocate \c m_VirtualImage with the passed
   * information, with the pixel buffer left unallocated.
   * Metric evaluation will be performed within the constraints of the virtual
   * domain depending on implementation in derived classes.
   * A default domain is created during initialization in derived
   * classes according to their need.
   * \param spacing   spacing
   * \param origin    origin
   * \param direction direction
   * \param region    region is used to set all image regions.
   *
   * \sa SetVirtualDomainFromImage
   */
  void
  SetVirtualDomain(const VirtualSpacingType &   spacing,
                   const VirtualOriginType &    origin,
                   const VirtualDirectionType & direction,
                   const VirtualRegionType &    region);

  /** Use a virtual domain image to define the virtual reference space.
   * \sa SetVirtualDomain */
  void
  SetVirtualDomainFromImage(const VirtualImageType * virtualImage);

  /** Returns a flag. True if arbitrary virtual domain points will
   *  always correspond to data points. False if not. For example,
   *  point-set metrics return false because only some virtual domain
   *  points will correspond to points within the point sets. */
  virtual bool
  SupportsArbitraryVirtualDomainSamples() const = 0;

  /** Return a timestamp relating to the virtual domain.
   * This returns the greater of the metric timestamp and the
   * virtual domain image timestamp. This allows us to
   * capture if the virtual domain image is changed by the user
   * after being assigned to the metric. */
  virtual const TimeStamp &
  GetVirtualDomainTimeStamp() const;

  /** Accessors for the virtual domain spacing.
   *  Returns unit spacing if a virtual domain is undefined. */
  VirtualSpacingType
  GetVirtualSpacing() const;

  /** Accessor for virtual domain origin.
   *  Returns zero origin if a virtual domain is undefined. */
  VirtualOriginType
  GetVirtualOrigin() const;

  /** Accessor for virtual domain direction.
   *  Returns unit direction if a virtual domain is undefined. */
  VirtualDirectionType
  GetVirtualDirection() const;

  /** Return the virtual domain region, which is retrieved from
   *  the m_VirtualImage buffered region. */
  const VirtualRegionType &
  GetVirtualRegion() const;

  itkGetModifiableObjectMacro(VirtualImage, VirtualImageType);

  /** Computes an offset for accessing parameter data from a virtual domain
   * index. Relevant for metrics with local-support transforms, to access
   * parameter or derivative memory that is stored linearly in a 1D array.
   * The result is the offset (1D array index) to the first of N parameters
   * corresponding to the given virtual index, where N is the number of
   * local parameters.
   * \param index the virtual index to convert
   * \param numberOfLocalParameters corresponding to the transform
   **/
  OffsetValueType
  ComputeParameterOffsetFromVirtualIndex(const VirtualIndexType &       index,
                                         const NumberOfParametersType & numberOfLocalParameters) const;

  /** Computes an offset for accessing parameter data from a virtual domain
   * point. Relevant for metrics with local-support transforms, to access
   * parameter or derivative memory that is stored linearly in a 1D array.
   * The result is the offset (1D array index) to the first of N parameters
   * corresponding to the given virtual index, where N is the number of
   * local parameters.
   * \param point the virtual point to convert
   * \param numberOfLocalParameters corresponding to the transform
   **/
  OffsetValueType
  ComputeParameterOffsetFromVirtualPoint(const VirtualPointType &       point,
                                         const NumberOfParametersType & numberOfLocalParameters) const;

  /** Determine if a point is within the virtual domain.
   * \note Returns true if the virtual domain has not been defined. This
   * allows, for example, use in point set metrics where the virtual domain
   * is implicitly defined by the point sets and transforms. */
  bool
  IsInsideVirtualDomain(const VirtualPointType & point) const;
  bool
  IsInsideVirtualDomain(const VirtualIndexType & index) const;

  using MetricCategoryType = typename Superclass::MetricCategoryEnum;

  /** Get metric category */
  MetricCategoryType
  GetMetricCategory() const override
  {
    return MetricCategoryType::OBJECT_METRIC;
  }

protected:
  ObjectToObjectMetric();
  ~ObjectToObjectMetric() override = default;

  void
  PrintSelf(std::ostream & os, Indent indent) const override;

  /** Verify that virtual domain and displacement field are the same size
   * and in the same physical space. */
  virtual void
  VerifyDisplacementFieldSizeAndPhysicalSpace();

  bool
  TransformPhysicalPointToVirtualIndex(const VirtualPointType &, VirtualIndexType &) const;
  void
  TransformVirtualIndexToPhysicalPoint(const VirtualIndexType &, VirtualPointType &) const;

  /** If the moving transform is a DisplacementFieldTransform, return it.
   *  If the moving transform is a CompositeTransform, the routine will check if the
   *  first (last to be added) transform is a DisplacementFieldTransform, and if so return it.
   *  Otherwise, return nullptr. */
  const MovingDisplacementFieldTransformType *
  GetMovingDisplacementFieldTransform() const;

  /** Check that the number of valid points is above a default
   * minimum (zero). If not, then return false, and assign to 'value' a value
   * indicating insufficient valid points were found during evaluation, and set
   * the derivative to zero. A warning is also output.
   * This functionality is provided as a separate method so derived classes
   * can use it without hardcoding the details. */
  bool
  VerifyNumberOfValidPoints(MeasureType & value, DerivativeType & derivative) const;

  /** Transforms */
  FixedTransformPointer  m_FixedTransform{};
  MovingTransformPointer m_MovingTransform{};

  VirtualImagePointer m_VirtualImage{};

  /** Flag that is set when user provides a virtual domain, either via
   * SetVirtualDomain() or SetVirtualDomainFromImage(). */
  bool m_UserHasSetVirtualDomain{};

  /** Store the number of points used during most recent value and derivative
   * calculation.
   * \sa VerifyNumberOfValidPoints() */
  mutable SizeValueType m_NumberOfValidPoints{ 0 };
};
} // end namespace itk

#ifndef ITK_MANUAL_INSTANTIATION
#  include "itkObjectToObjectMetric.hxx"
#endif

#endif
