itkIdentityTransform.h

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/*=========================================================================
 *
 *  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 itkIdentityTransform_h
#define itkIdentityTransform_h

#include "itkObject.h"
#include "itkPoint.h"
#include "itkCovariantVector.h"
#include "vnl/vnl_vector_fixed.h"
#include "itkArray2D.h"
#include "itkTransform.h"

namespace itk
{
template<typename TParametersValueType,
          unsigned int NDimensions=3>
class ITK_TEMPLATE_EXPORT IdentityTransform : public Transform<TParametersValueType, NDimensions, NDimensions>
{
public:
  ITK_DISALLOW_COPY_AND_ASSIGN(IdentityTransform);

  using Self = IdentityTransform;
  using Superclass = Transform<TParametersValueType, NDimensions, NDimensions>;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

  itkNewMacro(Self);

  itkTypeMacro(IdentityTransform, Transform);

  static constexpr unsigned int InputSpaceDimension = NDimensions;
  static constexpr unsigned int OutputSpaceDimension = NDimensions;

  using ParametersType = typename Superclass::ParametersType;
  using ParametersValueType = typename Superclass::ParametersValueType;
  using FixedParametersType = typename Superclass::FixedParametersType;
  using FixedParametersValueType = typename Superclass::FixedParametersValueType;
  using ScalarType = ParametersValueType;


  using JacobianType = typename Superclass::JacobianType;
  using JacobianPositionType = typename Superclass::JacobianPositionType;
  using InverseJacobianPositionType = typename Superclass::InverseJacobianPositionType;

  using TransformCategoryType = typename Superclass::TransformCategoryType;

  using InputVectorType = Vector<TParametersValueType,
                 Self::InputSpaceDimension>;
  using OutputVectorType = Vector<TParametersValueType,
                 Self::OutputSpaceDimension>;

  using InputCovariantVectorType = CovariantVector<TParametersValueType,
                          Self::InputSpaceDimension>;
  using OutputCovariantVectorType = CovariantVector<TParametersValueType,
                          Self::OutputSpaceDimension>;

  using InputVnlVectorType = vnl_vector_fixed<TParametersValueType,
                           Self::InputSpaceDimension>;
  using OutputVnlVectorType = vnl_vector_fixed<TParametersValueType,
                           Self::OutputSpaceDimension>;

  using InputPointType = Point<TParametersValueType,
                Self::InputSpaceDimension>;
  using OutputPointType = Point<TParametersValueType,
                Self::OutputSpaceDimension>;

  using InverseTransformBaseType = typename Superclass::InverseTransformBaseType;
  using InverseTransformBasePointer = typename InverseTransformBaseType::Pointer;

  OutputPointType TransformPoint(const InputPointType  & point) const override
  {
    return point;
  }

  using Superclass::TransformVector;
  OutputVectorType TransformVector(const InputVectorType & vector) const override
  {
    return vector;
  }

  OutputVnlVectorType TransformVector(const InputVnlVectorType & vector) const override
  {
    return vector;
  }

  using Superclass::TransformCovariantVector;
  OutputCovariantVectorType TransformCovariantVector(
    const InputCovariantVectorType & vector) const override
  {
    return vector;
  }

  void SetIdentity()
  {
  }

  void ComputeJacobianWithRespectToParameters( const InputPointType &,
                                                       JacobianType & jacobian) const override
  {
    jacobian = this->m_ZeroJacobian;
  }


  void ComputeJacobianWithRespectToPosition(const InputPointType &,
                                            JacobianPositionType & jac) const override
  {
    jac.set_identity();
  }
  using Superclass::ComputeJacobianWithRespectToPosition;

  /* Always returns true if not null, as an identity is it's own inverse */
  bool GetInverse( Self *inverseTransform ) const
  {
    return (inverseTransform != nullptr);
  }

  InverseTransformBasePointer GetInverseTransform() const override
  {
    return this->New().GetPointer();
  }

  TransformCategoryType GetTransformCategory() const override
  {
    return Self::Linear;
  }

  const FixedParametersType & GetFixedParameters() const override
  {
    return this->m_FixedParameters;
  }

  void SetFixedParameters(const FixedParametersType &) override
  {
  }

  const ParametersType & GetParameters() const override
  {
    return this->m_Parameters;
  }

  void SetParameters(const ParametersType &) override
  {
  }

protected:
  IdentityTransform() : Transform<TParametersValueType, NDimensions, NDimensions>(0),
    m_ZeroJacobian(NDimensions, 0)
  {
    // The Jacobian is constant, therefore it can be initialized in the
    // constructor.
    this->m_ZeroJacobian.Fill(0.0);
  }

  ~IdentityTransform() override = default;

private:
  JacobianType m_ZeroJacobian;
};
} // end namespace itk

#endif