#ifndef __itkTransformToVelocityFieldSource_h
#define __itkTransformToVelocityFieldSource_h

#include "itkTransform.h"
#include "itkImageSource.h"

namespace itk
{

/** \class TransformToVelocityFieldSource
 * \brief Generate a velocity field from a input transform. The
 * exponential of the velocity and the input transform should represent the
 * same spatial transformation.
 *
 * Currently, only linear transforms are supported. The algorithms works
 * by using the matrix logarithm of the linear transform parameters expressed
 * in homogeneous coordinates.
 *
 * Output information (spacing, size and direction) for the output
 * image should be set. This information has the normal defaults of
 * unit spacing, zero origin and identity direction. Optionally, the
 * output information can be obtained from a reference image. If the
 * reference image is provided and UseReferenceImage is On, then the
 * spacing, origin and direction of the reference image will be used.
 *
 * Since this filter produces an image which is a different size than
 * its input, it needs to override several of the methods defined
 * in ProcessObject in order to properly manage the pipeline execution model.
 * In particular, this filter overrides
 * ProcessObject::GenerateInputRequestedRegion() and
 * ProcessObject::GenerateOutputInformation().
 *
 * This filter is implemented as a multithreaded filter.  It provides a 
 * ThreadedGenerateData() method for its implementation.
 *
 * \author Florence Dru, INRIA and Tom Vercauteren, MKT
 * 
 * \ingroup GeometricTransforms
 */
template <class TOutputImage,
class TTransformPrecisionType=double>
class ITK_EXPORT TransformToVelocityFieldSource:
    public ImageSource<TOutputImage>
{
public:
  /** Standard class typedefs. */
  typedef TransformToVelocityFieldSource          Self;
  typedef ImageSource<TOutputImage>               Superclass;
  typedef SmartPointer<Self>                      Pointer;
  typedef SmartPointer<const Self>                ConstPointer;

  typedef TOutputImage                            OutputImageType;
  typedef typename OutputImageType::Pointer       OutputImagePointer;
  typedef typename OutputImageType::ConstPointer  OutputImageConstPointer;
  typedef typename OutputImageType::RegionType    OutputImageRegionType;
 
  /** Method for creation through the object factory. */
  itkNewMacro( Self );

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

  /** Number of dimensions. */
  itkStaticConstMacro( ImageDimension, unsigned int,
    TOutputImage::ImageDimension );

  /** Typedefs for transform. */
  typedef Transform<TTransformPrecisionType, 
    itkGetStaticConstMacro( ImageDimension ), 
    itkGetStaticConstMacro( ImageDimension )>     TransformType;
  typedef typename TransformType::ConstPointer    TransformConstPointerType;
  typedef typename TransformType::Pointer         TransformPointerType;

  /** Typedefs for output image. */
  typedef typename OutputImageType::PixelType     PixelType;
  typedef typename PixelType::ValueType           PixelValueType;
  typedef typename OutputImageType::RegionType    RegionType;
  typedef typename RegionType::SizeType           SizeType;
  typedef typename OutputImageType::IndexType     IndexType;
  typedef typename OutputImageType::PointType     PointType;
  typedef typename OutputImageType::SpacingType   SpacingType;
  typedef typename OutputImageType::PointType     OriginType;
  typedef typename OutputImageType::DirectionType DirectionType;

  /** Typedefs for base image. */
  typedef ImageBase< itkGetStaticConstMacro( ImageDimension ) > ImageBaseType;
  
  /** Set the coordinate transformation.
   * Set the coordinate transform to use for resampling.  Note that this must
   * be in physical coordinates and it is the output-to-input transform, NOT
   * the input-to-output transform that you might naively expect.  By default
   * the filter uses an Identity transform. You must provide a different
   * transform here, before attempting to run the filter, if you do not want to
   * use the default Identity transform. */
  itkSetConstObjectMacro( Transform, TransformType ); 

  /** Get a pointer to the coordinate transform. */
  itkGetConstObjectMacro( Transform, TransformType );

  /** Set the size of the output image. */
  virtual void SetOutputSize( const SizeType & size );

  /** Get the size of the output image. */
  virtual const SizeType & GetOutputSize();

  /** Set the start index of the output largest possible region. 
  * The default is an index of all zeros. */
  virtual void SetOutputIndex( const IndexType & index );

  /** Get the start index of the output largest possible region. */
  virtual const IndexType & GetOutputIndex();

  /** Set the region of the output image. */
  itkSetMacro( OutputRegion, OutputImageRegionType );

  /** Get the region of the output image. */
  itkGetConstReferenceMacro( OutputRegion, OutputImageRegionType );
     
  /** Set the output image spacing. */
  itkSetMacro( OutputSpacing, SpacingType );
  virtual void SetOutputSpacing( const double* values );

  /** Get the output image spacing. */
  itkGetConstReferenceMacro( OutputSpacing, SpacingType );

  /** Set the output image origin. */
  itkSetMacro( OutputOrigin, OriginType );
  virtual void SetOutputOrigin( const double* values);

  /** Get the output image origin. */
  itkGetConstReferenceMacro( OutputOrigin, OriginType );

  /** Set the output direction cosine matrix. */
  itkSetMacro( OutputDirection, DirectionType );
  itkGetConstReferenceMacro( OutputDirection, DirectionType );

  /** Helper method to set the output parameters based on this image */
  void SetOutputParametersFromImage( const ImageBaseType * image );
  
  /** TransformToVelocityFieldSource produces a vector image. */
  virtual void GenerateOutputInformation( void );

  /** Just checking if transform is set. */
  virtual void BeforeThreadedGenerateData( void );

  /** Compute the Modified Time based on changes to the components. */
  unsigned long GetMTime( void ) const;

#ifdef ITK_USE_CONCEPT_CHECKING
  /** Begin concept checking */
  itkStaticConstMacro(PixelDimension, unsigned int,
                      PixelType::Dimension );
  itkConceptMacro(SameDimensionCheck,
    (Concept::SameDimension<ImageDimension,PixelDimension>));
  /** End concept checking */
#endif

protected:
  TransformToVelocityFieldSource( void );
  ~TransformToVelocityFieldSource( void ) {};

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

  /** TransformToVelocityFieldSource can be implemented as a multithreaded
   * filter. */
  void DynamicThreadedGenerateData(
    const OutputImageRegionType & outputRegionForThread);

  /** Faster implementation for resampling that works for with linear
   *  incremental transformation types. */
  void LinearThreadedGenerateData(
    const OutputImageRegionType & outputRegionForThread);
  
private:

  TransformToVelocityFieldSource( const Self& ); //purposely not implemented
  void operator=( const Self& ); //purposely not implemented

  /** Member variables. */
  RegionType              m_OutputRegion;      // region of the output image
  SpacingType             m_OutputSpacing;     // output image spacing
  OriginType              m_OutputOrigin;      // output image origin
  DirectionType           m_OutputDirection;   // output image direction cosines
  TransformConstPointerType m_Transform;       // Input transform to use
  TransformConstPointerType m_IncrementalTransform; // Corresponding incremental transform
}; // end class TransformToVelocityFieldSource
  
} // end namespace itk
  
#ifndef ITK_MANUAL_INSTANTIATION
#include "itkTransformToVelocityFieldSource.txx"
#endif
  
#endif // end #ifndef __itkTransformToVelocityFieldSource_h