itkIdentityTransform.h

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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 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 VDimension = 3>
class ITK_TEMPLATE_EXPORT IdentityTransform : public Transform<TParametersValueType, VDimension, VDimension>
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(IdentityTransform);

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

  itkNewMacro(Self);

  itkOverrideGetNameOfClassMacro(IdentityTransform);

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

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

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

  using typename Superclass::TransformCategoryEnum;

  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.SetSize(VDimension, 0);
  }

  void
  ComputeJacobianWithRespectToPosition(const InputPointType &, JacobianPositionType & jac) const override
  {
    jac.set_identity();
  }
 
  using Superclass::ComputeJacobianWithRespectToPosition;
 
  /* Always returns true if not null, as an identity is its own inverse */
  bool
  GetInverse(Self * inverseTransform) const
  {
    return (inverseTransform != nullptr);
  }

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

  TransformCategoryEnum
  GetTransformCategory() const override
  {
    return Self::TransformCategoryEnum::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() = default;
  ~IdentityTransform() override = default;
};
} // end namespace itk
 
#endif