/*=========================================================================
 *
 *  Copyright Insight Software Consortium
 *
 *  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:
  /** Standard class typedefs. */
  typedef RegistrationParameterScalesFromJacobian         Self;
  typedef RegistrationParameterScalesEstimator< TMetric > Superclass;
  typedef SmartPointer<Self>                              Pointer;
  typedef SmartPointer<const Self>                        ConstPointer;

  /** New macro for creation of through a Smart Pointer. */
  itkNewMacro( Self );

  /** Run-time type information (and related methods). */
  itkTypeMacro( RegistrationParameterScalesFromJacobian, RegistrationParameterScalesEstimator );

  /** Type of scales */
  typedef typename Superclass::ScalesType                ScalesType;
  /** Type of parameters of the optimizer */
  typedef typename Superclass::ParametersType            ParametersType;
  /** Type of float */
  typedef typename Superclass::FloatType                 FloatType;

  typedef typename Superclass::VirtualPointType          VirtualPointType;
  typedef typename Superclass::VirtualIndexType          VirtualIndexType;
  typedef typename Superclass::MovingTransformType       MovingTransformType;
  typedef typename Superclass::FixedTransformType        FixedTransformType;
  typedef typename Superclass::JacobianType              JacobianType;
  typedef typename Superclass::VirtualImageConstPointer  VirtualImageConstPointer;

  /** Estimate parameter scales. */
  virtual void EstimateScales(ScalesType &scales) ITK_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.
   */
  virtual FloatType EstimateStepScale(const ParametersType &step) ITK_OVERRIDE;

  /** Estimate the scales of local steps. */
  virtual void EstimateLocalStepScales(const ParametersType &step,
    ScalesType &localStepScales) ITK_OVERRIDE;

protected:
  RegistrationParameterScalesFromJacobian();
  ~RegistrationParameterScalesFromJacobian() ITK_OVERRIDE {};

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

private:
  ITK_DISALLOW_COPY_AND_ASSIGN(RegistrationParameterScalesFromJacobian);

}; //class RegistrationParameterScalesFromJacobian


}  // namespace itk


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

#endif /* itkRegistrationParameterScalesFromJacobian_h */