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/*========================================================================= |
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Program: Insight Segmentation & Registration Toolkit |
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Module: $RCSfile: itkFiniteDifferenceFunction.h.html,v $ |
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Language: C++ |
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Date: $Date: 2006/01/17 19:15:35 $ |
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Version: $Revision: 1.4 $ |
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Copyright (c) Insight Software Consortium. All rights reserved. |
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See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details. |
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This software is distributed WITHOUT ANY WARRANTY; without even |
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the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR |
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PURPOSE. See the above copyright notices for more information. |
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=========================================================================*/ |
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#ifndef __itkFiniteDifferenceFunction_h_ |
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#define __itkFiniteDifferenceFunction_h_ |
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#include "itkLightObject.h" |
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#include "itkConstNeighborhoodIterator.h" |
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#include "itkZeroFluxNeumannBoundaryCondition.h" |
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#include "itkVector.h" |
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#include "itkFixedArray.h" |
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namespace itk { |
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/** |
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* \class FiniteDifferenceFunction |
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* |
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* This class is a component object of the finite difference solver hierarchy |
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* (see itkFiniteDifferenceImageFilter). It defines a generic interface for a |
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* function object that computes a single scalar value from a neighborhood of |
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* values. Examples of the application of this class are the various flavors |
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* of AnisotropicDiffusionFunctions and LevelSetFunction objects. |
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* |
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* These functions calculate the incremental change at a pixel in the solution |
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* image from one iteration of the p.d.e. solver to the next. |
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* |
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* \par |
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* Subclasses of FiniteDifferenceImageFilter (solvers) call the |
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* ComputeUpdate() method of this class to compute \f$ \Delta u^n_{\mathbf{i}} |
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* \f$ at each \f$ i \f$. in \f$ u \f$. Because the size of the time step for |
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* each iteration of the p.d.e. solution depends on the particular calculations |
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* done, this function object is also responsible for computing that time step |
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* (see ComputeGlobalTimeStep). |
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* |
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* \par How to use this class |
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* FiniteDifferenceFunction must be subclassed to add functionality for |
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* ComputeUpdate, ComputeGlobalTimeStep, and Get/ReleaseGlobalDataPointer. |
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* |
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* \par A note on thread safety. |
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template<class TImageType> |
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* The ComputeUpdate() methods of this filter are declared as const to enforce |
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* thread-safety during execution of FiniteDifferenceImageFilter solver |
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* algorithms. The InitializeIteration() method is intended to provide a safe |
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* way to modify the state of the object between threaded calculations of |
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* solvers. |
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* |
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* \todo Possibly subclass this object from Function. Stumbling blocks here |
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* are the specialized api of FiniteDifferenceFunction. |
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* |
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* \ingroup Functions */ |
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template<class TImageType> |
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class ITK_EXPORT FiniteDifferenceFunction : public LightObject |
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{ |
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public: |
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/** Standard class typedefs. */ |
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typedef FiniteDifferenceFunction Self; |
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TDA |
typedef LightObject Superclass; |
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typedef SmartPointer<Self> Pointer; |
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typedef SmartPointer<const Self> ConstPointer; |
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/** Run-time type information (and related methods) */ |
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itkTypeMacro( FiniteDifferenceFunction, LightObject ); |
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/** Extract some parameters from the image type */ |
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typedef TImageType ImageType; |
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TDA |
typedef typename ImageType::PixelType PixelType; |
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typedef double PixelRealType; |
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/** Save image dimension. */ |
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itkStaticConstMacro(ImageDimension, unsigned int, ImageType::ImageDimension); |
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/** Define the TimeStepType to always be double. */ |
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typedef double TimeStepType; |
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/** The default boundary condition for finite difference |
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* functions that is used unless overridden in the Evaluate() method. */ |
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typedef ZeroFluxNeumannBoundaryCondition<ImageType> |
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****DefaultBoundaryConditionType; |
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/** Neighborhood radius type */ |
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typedef typename ConstNeighborhoodIterator<TImageType>::RadiusType RadiusType; |
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/** The type of data structure that is passed to this function object |
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* to evaluate at a pixel that does not lie on a data set boundary. */ |
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typedef ConstNeighborhoodIterator<TImageType, DefaultBoundaryConditionType> NeighborhoodType; |
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/** A floating point offset from an image grid location. Used for |
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* interpolation among grid values in a neighborhood. */ |
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typedef Vector<float,itkGetStaticConstMacro(ImageDimension)> FloatOffsetType; |
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/** This method allows the function to set its state before each iteration |
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* of the finite difference solver (image filter) that uses it. This is |
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* a thread-safe time to manipulate the object's state. |
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* |
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* An example of how this can be used: the Anisotropic diffusion class of |
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* FiniteDifferenceFunctions use this method to pre-calculate an average |
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* gradient magnitude across the entire image region. This value is set in |
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* the function object and used by the ComputeUpdate methods that are called |
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* at each pixel as a constant. */ |
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virtual void InitializeIteration() {}; |
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/** This method is called by a finite difference solver image filter at |
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* each pixel that does not lie on a data set boundary. The width of the |
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* data set boundary is defined by the width of the neighborhood being |
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* evaluated. |
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* |
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* The neighborhood argument is the neighborhood data. |
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* The globalData argument is a pointer to a data structure that holds |
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* values that need to be persistent across calls to this function, but |
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* cannot be stored in the function object itself for thread-safety reasons. |
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* Examples are values needed to compute the time-step for an iteration |
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* of the solver. |
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* \sa InitializeIteration |
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* \sa ComputeGlobalTimeStep */ |
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virtual PixelType ComputeUpdate(const NeighborhoodType &neighborhood, |
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void *globalData, |
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const FloatOffsetType &offset = FloatOffsetType(0.0)) = 0; |
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/** Sets the radius of the neighborhood this FiniteDifferenceFunction |
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* needs to perform its calculations. */ |
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void SetRadius(const RadiusType &r) |
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{ m_Radius = r; } |
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/** Returns the radius of the neighborhood this FiniteDifferenceFunction |
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* needs to perform its calculations. */ |
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const RadiusType &GetRadius() const |
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{ return m_Radius; } |
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/** Set the ScaleCoefficients for the difference |
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* operators. The defaults a 1.0. These can be set to take the image |
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* spacing into account. */ |
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void SetScaleCoefficients (PixelRealType vals[ImageDimension]) |
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{ |
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******for (unsigned int i = 0; i < ImageDimension; i++) |
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********{ |
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********m_ScaleCoefficients[i] = vals[i]; |
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********} |
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} |
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/** Computes the time step for an update given a global data structure. |
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* The data used in the computation may take different forms depending on |
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* the nature of the equations. This global data cannot be kept in the |
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* instance of the equation object itself since the equation object must |
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* remain stateless for thread safety. The global data is therefore managed |
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* for each thread by the finite difference solver filters. */ |
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virtual TimeStepType ComputeGlobalTimeStep(void *GlobalData) const =0; |
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/** Returns a pointer to a global data structure that is passed to this |
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* object from the solver at each calculation. The idea is that the |
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* solver holds the state of any global values needed to calculate the |
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* time step, while the equation object performs the actual calculations. |
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* |
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* The global data should also be initialized in this method. |
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* */ |
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virtual void *GetGlobalDataPointer() const =0; |
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/** When the finite difference solver filter has finished using a global |
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* data pointer, it passes it to this method, which frees the memory. |
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* |
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* The solver cannot free the memory because it does not know the type |
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* to which the pointer points. */ |
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virtual void ReleaseGlobalDataPointer(void *GlobalData) const =0; |
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protected: |
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FiniteDifferenceFunction() |
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**{ |
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// initialize variables |
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m_Radius.Fill( 0 ); |
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for (unsigned int i = 0; i < ImageDimension; i++) |
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{ |
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m_ScaleCoefficients[i] = 1.0; |
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} |
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**} |
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~FiniteDifferenceFunction() {} |
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void PrintSelf(std::ostream& os, Indent indent) const; |
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RadiusType m_Radius; |
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PixelRealType m_ScaleCoefficients[ImageDimension]; |
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private: |
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FiniteDifferenceFunction(const Self&); //purposely not implemented |
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void operator=(const Self&); //purposely not implemented |
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}; |
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} // end namespace itk |
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#ifndef ITK_MANUAL_INSTANTIATION |
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#include "itkFiniteDifferenceFunction.txx" |
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#endif |
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#endif |
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