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A C++ implementation of Douglas-Peucker Line Approximation Algorithm

, 3 Mar 2003 633.4K 11.2K 120
DP Line approximation algorithm is a well-known method to approximate 2D lines. It is quite fast, O(nlog_2(n)) for a n-points line and can drastically compress a data curve. Here, a fully OOP implementation is given.
// Containers.h: interface for the CContainers class.
//
//////////////////////////////////////////////////////////////////////

#if !defined(AFX_CONTAINERS_H__33EAD324_F802_4BC8_BEC8_39E69C1C21A7__INCLUDED_)
#define AFX_CONTAINERS_H__33EAD324_F802_4BC8_BEC8_39E69C1C21A7__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

#include <vector>
#include <list>

namespace hull
{

/*!
	\defgroup DCGroup Double container groups
	\ingroup LAGroup
*/

/*! \brief Virtual base class for Point double container

\ingroup DCGroup	
*/
template<typename T, typename TVectorX, typename TVectorY>
class TPointDoubleContainerBase
{
public:
	//! \name Typedefs
	//@{
	typedef TPoint<T> value_type;
	typedef TPointRef<T> reference;
	typedef TVectorX container_x;
	typedef TVectorY container_y;
	//@}

	/*! \brief Constructor

	\param pX pointer to x coordinate container,
	\param pY pointer to y coordinate container
	*/
	TPointDoubleContainerBase(container_x* pX = NULL, container_y* pY =NULL):m_pX(pX),m_pY(pY){};
	virtual ~TPointDoubleContainerBase(){};
	
	//! return the size of the point container
	size_t size() const			{	ASSERT(m_pX); ASSERT(m_pY); return __min( m_pX->size(), m_pY->size());};
	/*! \brief resize the container
	
	\param size the new size of the vector.
	*/
	void resize(size_t size)	{	ASSERT(m_pX); ASSERT(m_pY); m_pX->resize(size); m_pY->resize(size);};

	//! return the value at position i
	value_type operator[](UINT i) const	{	return value_type((*m_pX)[i],(*m_pY)[i]);};
	//! return a reference to position i
	reference operator[](UINT i)		{	return reference((*m_pX)[i],(*m_pY)[i]);};

	//! Sets the container pointers
	void SetContainers( container_x* pX, container_y* pY)	{	m_pX=pX; m_pY=pY;};
	//! return the x coordinate pointer, const
	const container_x* GetXContainer() const		{	return m_pX;};
	//! return the y coordinate pointer, const
	const container_y* GetYContainer() const		{	return m_pY;};
	//! return the x coordinate pointer
	container_x* GetXContainer()					{	return m_pX;};
	//! return the y coordinate pointer
	container_y* GetYContainer()					{	return m_pY;};

protected:
	container_x* m_pX;
	container_y* m_pY;
};

/*! \brief Base class for point iterator

\param T float or double
\param TVectorX x coordinate container with random access iterator
\param TVectorY y coordinate container with random access iterator

	A random access iterator base class.

  \ingroup DCGroup
*/
template<typename T,typename TVectorX, typename TVectorY>
class TPointIt
{
public:
	TPointIt(const TPointDoubleContainerBase<T,TVectorX,TVectorY>* pV = NULL, UINT index = 0):m_pV(pV),m_index(index){};
	virtual ~TPointIt(){};

	TPointIt<T,TVectorX,TVectorY>& operator = (const TPointIt<T,TVectorX,TVectorY>& t)	
	{	
		if (&t!=this)
		{
			m_pV=t.m_pV;
			m_index=t.m_index;
		};
		return *this;
	};

	friend UINT operator - (const TPointIt<T,TVectorX,TVectorY>& t1, const TPointIt<T,TVectorX,TVectorY>& t2){	return t1.m_index-t2.m_index; };

	friend bool operator == ( const TPointIt<T,TVectorX,TVectorY>& t1, const TPointIt<T,TVectorX,TVectorY>& t2)	{	return t1.m_index==t2.m_index && t1.m_pV==t2.m_pV;};
	friend bool operator != ( const TPointIt<T,TVectorX,TVectorY>& t1, const TPointIt<T,TVectorX,TVectorY>& t2)	{	return  t1.m_index!=t2.m_index || t1.m_pV!=t2.m_pV;};
	friend bool operator < ( const TPointIt<T,TVectorX,TVectorY>& t1, const TPointIt<T,TVectorX,TVectorY>& t2)	{	return  t1.m_index<t2.m_index;};
	friend bool operator > ( const TPointIt<T,TVectorX,TVectorY>& t1, const TPointIt<T,TVectorX,TVectorY>& t2)	{	return  t1.m_index>t2.m_index;};
	friend bool operator <= ( const TPointIt<T,TVectorX,TVectorY>& t1, const TPointIt<T,TVectorX,TVectorY>& t2)	{	return  t1.m_index<=t2.m_index;};
	friend bool operator >= ( const TPointIt<T,TVectorX,TVectorY>& t1, const TPointIt<T,TVectorX,TVectorY>& t2)	{	return  t1.m_index>=t2.m_index;};

protected:
	long m_index;
	const TPointDoubleContainerBase<T,TVectorX,TVectorY>* m_pV;
};

/*! \brief PointDoubleContainer iterator

\param T float or double
\param TVectorX x coordinate container with random access iterator
\param TVectorY y coordinate container with random access iterator

  A random access iterator.

  \ingroup DCGroup
*/
template<typename T, typename TVectorX, typename TVectorY>
class TPointRandIt : public TPointIt<T,TVectorX,TVectorY>
{
public:
	TPointRandIt(const TPointDoubleContainerBase<T,TVectorX,TVectorY>* pV = NULL, UINT index = 0):TPointIt<T,TVectorX,TVectorY>(pV,index)
	{};
	TPointRandIt<T,TVectorX,TVectorY>& operator = (const TPointRandIt<T,TVectorX,TVectorY>& t)	
	{	
		if (&t!=this)
		{
			TPointIt<T,TVectorX,TVectorY>::operator=(t);
		};
		return *this;
	};


	TPoint<T> operator*() const			
	{	
		ASSERT(m_pV); 
		ASSERT(m_index<m_pV->size()); 
		return TPoint<T>((*m_pV->GetXContainer())[m_index], (*m_pV->GetYContainer())[m_index]);
	};

	TPointRef<T> operator*()						
	{	
		ASSERT(m_pV); 
		ASSERT(m_index<m_pV->size());
		return TPointRef<T>( (*m_pV->GetXContainer())[m_index], (*m_pV->GetYContainer())[m_index]);
	};

	TPointRandIt<T,TVectorX,TVectorY>& operator++(int)				{	return TPointRandIt<T,TVectorX,TVectorY>( m_pV, m_index+1); };
	TPointRandIt<T,TVectorX,TVectorY>& operator--(int)				{	return TPointRandIt<T,TVectorX,TVectorY>( m_pV, m_index-1); };
	TPointRandIt<T,TVectorX,TVectorY>& operator++()					{	m_index++; return *this; };
	TPointRandIt<T,TVectorX,TVectorY>& operator--()					{	m_index--; return *this; };
	TPointRandIt<T,TVectorX,TVectorY>& operator+=(UINT i)			{	m_index+=i; return *this; };
	TPointRandIt<T,TVectorX,TVectorY>& operator-=(UINT i)			{	m_index-=i;  return *this; };
	friend TPointRandIt<T,TVectorX,TVectorY> operator + (const TPointRandIt<T,TVectorX,TVectorY>& t, UINT i)	{	return TPointRandIt<T,TVectorX,TVectorY>( t.m_pV, t.m_index+i);};
	friend TPointRandIt<T,TVectorX,TVectorY> operator - (const TPointRandIt<T,TVectorX,TVectorY>& t, UINT i)	{	return TPointRandIt<T,TVectorX,TVectorY>( t.m_pV, t.m_index-i);};

};

/*! \brief PointDoubleContainer const_iterator

\param T float or double
\param TVectorX x coordinate container with random access iterator
\param TVectorY y coordinate container with random access iterator

	A const random access iterator.

  \ingroup DCGroup
*/
template<typename T, typename TVectorX, typename TVectorY>
class TPointConstRandIt : public TPointIt<T,TVectorX,TVectorY>
{
public:
	TPointConstRandIt(const TPointDoubleContainerBase<T,TVectorX,TVectorY>* pV = NULL, UINT index = 0):TPointIt<T,TVectorX,TVectorY>(pV,index){};

	TPointConstRandIt& operator = (const TPointConstRandIt<T,TVectorX,TVectorY>& t)	
	{	
		if (&t!=this)
		{
			TPointIt<T,TVectorX,TVectorY>::operator=(t);
		};
		return *this;
	};

	TPointConstRandIt& operator = (const TPointRandIt<T,TVectorX,TVectorY>& t)	
	{	
		TPointIt<T,TVectorX,TVectorY>::operator=(t);
		return *this;
	};

	TPoint<T> operator*() const							
	{			
		ASSERT(m_pV); 
		ASSERT(m_index<m_pV->size());	
		return TPoint<T>((*m_pV->GetXContainer())[m_index], (*m_pV->GetYContainer())[m_index]);
	};

	TPointConstRandIt<T,TVectorX,TVectorY>& operator++(int)				{	return TPointConstRandIt<T,TVectorX,TVectorY>( t.m_pV, m_index+1); };
	TPointConstRandIt<T,TVectorX,TVectorY>& operator--(int)				{	return TPointConstRandIt<T,TVectorX,TVectorY>( t.m_pV, m_index-1); };
	TPointConstRandIt<T,TVectorX,TVectorY>& operator++()					{	m_index++; return *this; };
	TPointConstRandIt<T,TVectorX,TVectorY>& operator--()					{	m_index--; return *this; };
	TPointConstRandIt<T,TVectorX,TVectorY>& operator+=(UINT i)			{	m_index+=i; return *this; };
	TPointConstRandIt<T,TVectorX,TVectorY>& operator-=(UINT i)			{	m_index-=i;  return *this; };
	friend TPointConstRandIt<T,TVectorX,TVectorY> operator + (const TPointConstRandIt<T,TVectorX,TVectorY>& t, UINT i)	{	return TPointConstRandIt<T,TVectorX,TVectorY>( t.m_pV, t.m_index+i);};
	friend TPointConstRandIt<T,TVectorX,TVectorY> operator - (const TPointConstRandIt<T,TVectorX,TVectorY>& t, UINT i)	{	return TPointConstRandIt<T,TVectorX,TVectorY>( t.m_pV, t.m_index-i);};
};

/*! \brief A container linking two separate containers into a point container

\param T float or double
\param TVectorX x coordinate container with random access iterator
\param TVectorY y coordinate container with random access iterator

  \ingroup DCGroup
*/
template<typename T, typename TVectorX, typename TVectorY>
class TPointDoubleContainer : virtual public TPointDoubleContainerBase<T,TVectorX,TVectorY>
{
public:
	TPointDoubleContainer(TVectorX* pX = NULL, TVectorY* pY =NULL):TPointDoubleContainerBase<T,TVectorX,TVectorY>(pX,pY){};
	virtual~TPointDoubleContainer(){};

	typedef TPointConstRandIt<T,TVectorX,TVectorY> const_iterator;
	typedef TPointRandIt<T,TVectorX,TVectorY> iterator;

	iterator begin()	{	return iterator(this,0); };
	iterator end()		{	return iterator(this,size()); };

	const_iterator begin() const	{	return const_iterator(this,0); };
	const_iterator end() const		{	return const_iterator(this,size()); };
};

/*! \brief A container to export point to two containers

\param T float or double
\param TListX x coordinate container with single direction iterator
\param TListY y coordinate container with single direction iterator
\param TPointContainer The point container

	\ingroup DCGroup
*/
template<typename T, typename TListX, typename TListY, typename TPointContainer>
class TKeyDoubleContainer
{
public:
	typedef TPointContainer::const_iterator value_type;
	typedef TListX container_x;
	typedef TListY container_y;

	TKeyDoubleContainer( container_x* pListX = NULL, container_y* pListY = NULL):m_pListX(pListX), m_pListY(pListY){};

	void SetContainers( container_x* pListX, container_y* pListY)		{	m_pListX=pListX; m_pListY=pListY;};
	container_x* GetXContainer()										{	return m_pListX;};
	container_y* GetYContainer()										{	return m_pListY;};
	const container_x* GetXContainer() const							{	return m_pListX;};
	const container_y* GetYContainer() const							{	return m_pListY;};

	void clear()		{	ASSERT(m_pListX); ASSERT(m_pListY); m_pListX->clear(); m_pListY->clear();};
	size_t size() const	{	ASSERT(m_pListX); ASSERT(m_pListY); return __min( m_pListX->size(), m_pListY->size());};

	void push_back( const value_type& p)	{ ASSERT(m_pListX); ASSERT(m_pListY); m_pListX->push_back((*p).x); m_pListY->push_back((*p).y);};
	void push_front( const value_type& p)	{ ASSERT(m_pListX); ASSERT(m_pListY); m_pListX->push_front((*p).x); m_pListY->push_front((*p).y);};

protected:
	container_x* m_pListX;
	container_y* m_pListY;
};



};

#endif // !defined(AFX_CONTAINERS_H__33EAD324_F802_4BC8_BEC8_39E69C1C21A7__INCLUDED_)

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About the Author

Jonathan de Halleux
Engineer
United States United States
Jonathan de Halleux is Civil Engineer in Applied Mathematics. He finished his PhD in 2004 in the rainy country of Belgium. After 2 years in the Common Language Runtime (i.e. .net), he is now working at Microsoft Research on Pex (http://research.microsoft.com/pex).

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