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 itkRegistrationParameterScalesFromJacobian_h
  #define itkRegistrationParameterScalesFromJacobian_h
  
  #include "itkRegistrationParameterScalesEstimator.h"
  
  namespace itk
  {
  
  /**
   *\class RegistrationParameterScalesFromJacobian
   *  \brief Implements a registration helper class for estimating scales of
   * transform parameters from Jacobian norms.
   *
   * Its input includes the fixed/moving images and transform objects,
   * which can be obtained from the metric object.
   *
   * The scale of a parameter is estimated from the averaged squared norm of
   * the Jacobian w.r.t the parameter. The averaging is done over a sampling
   * of the image domain. The sampling by default is a uniform random
   * distribution.
   *
   * \ingroup ITKOptimizersv4
   */
  template <typename TMetric>
  class ITK_TEMPLATE_EXPORT RegistrationParameterScalesFromJacobian : public RegistrationParameterScalesEstimator<TMetric>
  {
  public:
    ITK_DISALLOW_COPY_AND_MOVE(RegistrationParameterScalesFromJacobian);
  
    /** Standard class type aliases. */
    using Self = RegistrationParameterScalesFromJacobian;
    using Superclass = RegistrationParameterScalesEstimator<TMetric>;
    using Pointer = SmartPointer<Self>;
    using ConstPointer = SmartPointer<const Self>;
  
    /** New macro for creation of through a Smart Pointer. */
    itkNewMacro(Self);
  
    /** Run-time type information (and related methods). */
    itkTypeMacro(RegistrationParameterScalesFromJacobian, RegistrationParameterScalesEstimator);
  
    /** Type of scales */
    using ScalesType = typename Superclass::ScalesType;
    /** Type of parameters of the optimizer */
    using ParametersType = typename Superclass::ParametersType;
    /** Type of float */
    using FloatType = typename Superclass::FloatType;
  
    using VirtualPointType = typename Superclass::VirtualPointType;
    using VirtualIndexType = typename Superclass::VirtualIndexType;
    using MovingTransformType = typename Superclass::MovingTransformType;
    using FixedTransformType = typename Superclass::FixedTransformType;
    using JacobianType = typename Superclass::JacobianType;
    using VirtualImageConstPointer = typename Superclass::VirtualImageConstPointer;
  
    /** Estimate parameter scales. */
    void
    EstimateScales(ScalesType & scales) override;
  
    /**
     *  Estimate the scale for \f$\Delta p\f$, the step of change on parameters.
     *  The step scale describes the impact of \f$\Delta p\f$ on the transform.
     *
     *  Let us denote the transform by
     *  \f[ T(x, p) = T(x, p_0 + t * \Delta p) \f]
     *  where \f$x\f$ is the coordinates of a voxel, \f$p = p_0+t*\Delta p\f$ is
     *  the transform parameters, and \f$t\f$ is the step factor.
     *
     *  At a specific voxel at \f$x\f$, the step scale w.r.t. \f$\Delta p\f$ is
     *  defined here as
     *
     *  \f[ |\frac{dT}{dt}| = |\frac{\partial T}{\partial p} * \Delta p |. \f]
     *
     *  For multiple voxels, we average the above formula to get the overall
     *  step scale.
     */
    FloatType
    EstimateStepScale(const ParametersType & step) override;
  
    /** Estimate the scales of local steps. */
    void
    EstimateLocalStepScales(const ParametersType & step, ScalesType & localStepScales) override;
  
  protected:
    RegistrationParameterScalesFromJacobian() = default;
    ~RegistrationParameterScalesFromJacobian() override = default;
  
    void
    PrintSelf(std::ostream & os, Indent indent) const override;
  
    /**
     *  Compute the step scales for samples, i.e. the impacts on each sampled
     *  voxel from a change on the transform.
     */
    void
    ComputeSampleStepScales(const ParametersType & step, ScalesType & sampleScales);
  }; // class RegistrationParameterScalesFromJacobian
  
  
  } // namespace itk
  
  
  #ifndef ITK_MANUAL_INSTANTIATION
  #  include "itkRegistrationParameterScalesFromJacobian.hxx"
  #endif
  
  #endif /* itkRegistrationParameterScalesFromJacobian_h */
  