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 IdentityTransform : public Transform<TParametersValueType, NDimensions, NDimensions>
{
public:
  typedef IdentityTransform                                           Self;
  typedef Transform<TParametersValueType, NDimensions, NDimensions> Superclass;
  typedef SmartPointer<Self>                                        Pointer;
  typedef SmartPointer<const Self>                                  ConstPointer;

  itkNewMacro(Self);

  itkTypeMacro(IdentityTransform, Transform);

  itkStaticConstMacro(InputSpaceDimension, unsigned int, NDimensions);
  itkStaticConstMacro(OutputSpaceDimension, unsigned int, NDimensions);

  typedef typename Superclass::ParametersType           ParametersType;
  typedef typename Superclass::ParametersValueType      ParametersValueType;
  typedef typename Superclass::FixedParametersType      FixedParametersType;
  typedef typename Superclass::FixedParametersValueType FixedParametersValueType;
  typedef ParametersValueType                           ScalarType;


  typedef typename Superclass::JacobianType JacobianType;

  typedef typename Superclass::TransformCategoryType TransformCategoryType;

  typedef Vector<TParametersValueType,
                 itkGetStaticConstMacro(InputSpaceDimension)>  InputVectorType;
  typedef Vector<TParametersValueType,
                 itkGetStaticConstMacro(OutputSpaceDimension)> OutputVectorType;

  typedef CovariantVector<TParametersValueType,
                          itkGetStaticConstMacro(InputSpaceDimension)>  InputCovariantVectorType;
  typedef CovariantVector<TParametersValueType,
                          itkGetStaticConstMacro(OutputSpaceDimension)> OutputCovariantVectorType;

  typedef vnl_vector_fixed<TParametersValueType,
                           itkGetStaticConstMacro(InputSpaceDimension)>  InputVnlVectorType;
  typedef vnl_vector_fixed<TParametersValueType,
                           itkGetStaticConstMacro(OutputSpaceDimension)> OutputVnlVectorType;

  typedef Point<TParametersValueType,
                itkGetStaticConstMacro(InputSpaceDimension)> InputPointType;
  typedef Point<TParametersValueType,
                itkGetStaticConstMacro(OutputSpaceDimension)> OutputPointType;

  typedef typename Superclass::InverseTransformBaseType InverseTransformBaseType;
  typedef typename InverseTransformBaseType::Pointer    InverseTransformBasePointer;

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

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

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

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

  void SetIdentity(void)
  {
  }

  virtual void ComputeJacobianWithRespectToParameters( const InputPointType &,
                                                       JacobianType & jacobian) const ITK_OVERRIDE
  {
    jacobian = this->m_IdentityJacobian;
  }

  virtual void ComputeJacobianWithRespectToPosition(const InputPointType &,
                                                    JacobianType & jac) const ITK_OVERRIDE
  {
    jac.SetSize( NDimensions, NDimensions );
    jac.Fill(0.0);
    for( unsigned int dim = 0; dim < NDimensions; dim++ )
      {
      jac[dim][dim] = 1.0;
      }
  }

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

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

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

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

  virtual void SetFixedParameters(const FixedParametersType &) ITK_OVERRIDE
  {
  }

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

  virtual void SetParameters(const ParametersType &) ITK_OVERRIDE
  {
  }

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

  virtual ~IdentityTransform()
  {
  }

private:
  IdentityTransform(const Self &); // purposely not implemented
  void operator=(const Self &);    // purposely not implemented

  JacobianType m_IdentityJacobian;
};
} // end namespace itk

#endif