text: /*=========================================================================
   *
   *  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 itkVersorRigid3DTransformOptimizer_h
  #define itkVersorRigid3DTransformOptimizer_h
  
  #include "itkRegularStepGradientDescentOptimizer.h"
  #include "itkVersor.h"
  #include "ITKOptimizersExport.h"
  
  namespace itk
  {
  /** \class VersorRigid3DTransformOptimizer
   * \brief Implement a gradient descent optimizer for the VersorRigid3DTransform
   * parameter space.
   *
   * VersorRigid3DTransformOptimizer is a variant of the gradient descent
   * optimizer implmented in RegularStepGradientDescentOptimizer.
   *
   * Versors are not in a vector space, for that reason, the classical gradient
   * descent algorithm has to be modified in order to be applicable to Versors
   * (unit quaternions) that form the group SO(3).
   *
   * The Versor space has only three degrees of freedom, even though Versors are
   * represented using four values.
   *
   * This optimizer assumes that the CostFunction to be optimized has an
   * itk::Versor and an itk::Vector as parameters.
   *
   * \sa RegularStepGradientDescentOptimizer
   * \sa Versor
   * \sa VersorRigid3DTransform
   *
   * \ingroup Numerics Optimizers
   * \ingroup ITKOptimizers
   */
  class ITKOptimizers_EXPORT VersorRigid3DTransformOptimizer:
    public RegularStepGradientDescentBaseOptimizer
  {
  public:
    /** Standard class typedefs. */
    typedef VersorRigid3DTransformOptimizer         Self;
    typedef RegularStepGradientDescentBaseOptimizer Superclass;
    typedef SmartPointer< Self >                    Pointer;
    typedef SmartPointer< const Self >              ConstPointer;
  
    /** Method for creation through the object factory. */
    itkNewMacro(Self);
  
    /** Run-time type information (and related methods). */
    itkTypeMacro(VersorRigid3DTransformOptimizer,
                 RegularStepGradientDescentBaseOptimizer);
  
    /** This class is specialized for 3D  */
    itkStaticConstMacro(SpaceDimension, unsigned int, 6);
  
    /**  Versor Type  */
    typedef Versor< double >       VersorType;
    typedef VersorType::VectorType VectorType;
  
    /** Advance one step following the gradient direction. */
    virtual void StepAlongGradient(double factor,
                                   const DerivativeType & transformedGradient) ITK_OVERRIDE;
  
  protected:
    VersorRigid3DTransformOptimizer() {}
    virtual ~VersorRigid3DTransformOptimizer() {}
  
  private:
    VersorRigid3DTransformOptimizer(const Self &); //purposely not implemented
    void operator=(const Self &);                  //purposely not implemented
  };
  } // end namespace itk
  
  #endif
  