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

, 3 Mar 2003
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.
// TKeyExporter.h: interface for the TKeyExporter class.
//
//////////////////////////////////////////////////////////////////////

#if !defined(AFX_TKEYEXPORTER_H__F779C9D6_C433_4043_A8BB_CE2D10EC1F88__INCLUDED_)
#define AFX_TKEYEXPORTER_H__F779C9D6_C433_4043_A8BB_CE2D10EC1F88__INCLUDED_

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

#include <vector>
#include "LineApproximator.h"

namespace hull
{
/*
template <class T, class TPointContainer, class>
class TKeyVectorExporter : virtual public TLine<T, TPointContainer, TKeyContainer>  
{
public:
	//! \name Accessing data
	//@{
	//! fill vectors with keys
	void GetKeyToVector( std::vector<T>& vX, std::vector<T>& vY)
	{
		vX=m_vKeyX;
		vY=m_vKeyY;
	}
	//! return reference to vector of key x coordinates
	const TVector& GetKeyX() const		{	return m_vKeyX;};
	//! return reference to vector of key y coordinates
	const TVector& GetKeyY() const		{	return m_vKeyY;};
	//@}

protected:
	//! fill vectors with results
	virtual void ExportKeys();
private:
	TVector m_vKeyX;
	TVector m_vKeyY;
};

template<class T, class TPointContainer>
void TKeyVectorExporter<T,TPointContainer>::ExportKeys()
{
	const KeyContainer& kc=GetKeys();
	KeyContainer::const_iterator it;
	UINT i;

	m_vKeyX.resize(kc.size());
	m_vKeyY.resize(kc.size());

	for (it=kc.begin(), i=0; it!= kc.end();it++, i++)
	{
		m_vKeyX[i]=(*it)->x;
		m_vKeyY[i]=(*it)->y;
	}
}

template <class T,class TPointContainer>
class TKeyVectorPointerExporter : virtual public TLine<T,TPointContainer>  
{
public:
	//! \name Constructor
	//@{
	//! Constructor
	TKeyVectorPointerExporter( TVector* pX =NULL, TVector* pY=NULL): m_pKeyX(pX), m_pKeyY(pY){};
	//@}

	//! \name Accessing data
	//@{
	void SetKeyPointers( TVector* pX, TVector* pY)			{	m_pKeyX = pX; m_pKeyY=pY;};
	//! return reference to vector of key x coordinates, const
	const TVector* GetKeyX() const		{	return m_pKeyX;};
	//! return reference to vector of key y coordinates, const
	const TVector* GetKeyY() const		{	return m_pKeyY;};
	//! return reference to vector of key x coordinates
	TVector* GetKeyX()					{	return m_pKeyX;};
	//! return reference to vector of key y coordinates
	TVector* GetKeyY()					{	return m_pKeyY;};
	//@}

protected:
	//! fill vectors with results
	virtual void ExportKeys();
private:
	TVector* m_pKeyX;
	TVector* m_pKeyY;
};

template<class T,class TPointContainer>
void TKeyVectorPointerExporter<T,TPointContainer>::ExportKeys()
{
	const KeyContainer& kc=GetKeys();
	KeyContainer::const_iterator it;
	UINT i;

	if (!m_pKeyX || !m_pKeyY)
		return;

	m_pKeyX->resize(kc.size());
	m_pKeyY->resize(kc.size());

	for (it=kc.begin(), i=0; it!= kc.end();it++, i++)
	{
		(*m_pKeyX)[i]=(*it)->x;
		(*m_pKeyY)[i]=(*it)->y;
	}
}
*/
};

#endif // !defined(AFX_TKEYEXPORTER_H__F779C9D6_C433_4043_A8BB_CE2D10EC1F88__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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