Task: Ramer-Douglas-Peucker line simplification


C++: #include <iostream>
#include <cmath>
#include <utility>
#include <vector>
#include <stdexcept>
using namespace std;

typedef std::pair<double, double> Point;

double PerpendicularDistance(const Point &pt, const Point &lineStart, const Point &lineEnd)
{
	double dx = lineEnd.first - lineStart.first;
	double dy = lineEnd.second - lineStart.second;

	
	double mag = pow(pow(dx,2.0)+pow(dy,2.0),0.5);
	if(mag > 0.0)
	{
		dx /= mag; dy /= mag;
	}

	double pvx = pt.first - lineStart.first;
	double pvy = pt.second - lineStart.second;

	
	double pvdot = dx * pvx + dy * pvy;

	
	double dsx = pvdot * dx;
	double dsy = pvdot * dy;

	
	double ax = pvx - dsx;
	double ay = pvy - dsy;

	return pow(pow(ax,2.0)+pow(ay,2.0),0.5);
}

void RamerDouglasPeucker(const vector<Point> &pointList, double epsilon, vector<Point> &out)
{
	if(pointList.size()<2)
		throw invalid_argument("Not enough points to simplify");

	
	double dmax = 0.0;
	size_t index = 0;
	size_t end = pointList.size()-1;
	for(size_t i = 1; i < end; i++)
	{
		double d = PerpendicularDistance(pointList[i], pointList[0], pointList[end]);
		if (d > dmax)
		{
			index = i;
			dmax = d;
		}
	}

	
	if(dmax > epsilon)
	{
		
		vector<Point> recResults1;
		vector<Point> recResults2;
		vector<Point> firstLine(pointList.begin(), pointList.begin()+index+1);
		vector<Point> lastLine(pointList.begin()+index, pointList.end());
		RamerDouglasPeucker(firstLine, epsilon, recResults1);
		RamerDouglasPeucker(lastLine, epsilon, recResults2);
 
		
		out.assign(recResults1.begin(), recResults1.end()-1);
		out.insert(out.end(), recResults2.begin(), recResults2.end());
		if(out.size()<2)
			throw runtime_error("Problem assembling output");
	} 
	else 
	{
		
		out.clear();
		out.push_back(pointList[0]);
		out.push_back(pointList[end]);
	}
}

int main()
{
	vector<Point> pointList;
	vector<Point> pointListOut;

	pointList.push_back(Point(0.0, 0.0));
	pointList.push_back(Point(1.0, 0.1));
	pointList.push_back(Point(2.0, -0.1));
	pointList.push_back(Point(3.0, 5.0));
	pointList.push_back(Point(4.0, 6.0));
	pointList.push_back(Point(5.0, 7.0));
	pointList.push_back(Point(6.0, 8.1));
	pointList.push_back(Point(7.0, 9.0));
	pointList.push_back(Point(8.0, 9.0));
	pointList.push_back(Point(9.0, 9.0));

	RamerDouglasPeucker(pointList, 1.0, pointListOut);

	cout << "result" << endl;
	for(size_t i=0;i< pointListOut.size();i++)
	{
		cout << pointListOut[i].first << "," << pointListOut[i].second << endl;
	}

	return 0;
}




Java: import javafx.util.Pair;

import java.util.ArrayList;
import java.util.List;

public class LineSimplification {
    private static class Point extends Pair<Double, Double> {
        Point(Double key, Double value) {
            super(key, value);
        }

        @Override
        public String toString() {
            return String.format("(%f, %f)", getKey(), getValue());
        }
    }

    private static double perpendicularDistance(Point pt, Point lineStart, Point lineEnd) {
        double dx = lineEnd.getKey() - lineStart.getKey();
        double dy = lineEnd.getValue() - lineStart.getValue();

        
        double mag = Math.hypot(dx, dy);
        if (mag > 0.0) {
            dx /= mag;
            dy /= mag;
        }
        double pvx = pt.getKey() - lineStart.getKey();
        double pvy = pt.getValue() - lineStart.getValue();

        
        double pvdot = dx * pvx + dy * pvy;

        
        double ax = pvx - pvdot * dx;
        double ay = pvy - pvdot * dy;

        return Math.hypot(ax, ay);
    }

    private static void ramerDouglasPeucker(List<Point> pointList, double epsilon, List<Point> out) {
        if (pointList.size() < 2) throw new IllegalArgumentException("Not enough points to simplify");

        
        double dmax = 0.0;
        int index = 0;
        int end = pointList.size() - 1;
        for (int i = 1; i < end; ++i) {
            double d = perpendicularDistance(pointList.get(i), pointList.get(0), pointList.get(end));
            if (d > dmax) {
                index = i;
                dmax = d;
            }
        }

        
        if (dmax > epsilon) {
            List<Point> recResults1 = new ArrayList<>();
            List<Point> recResults2 = new ArrayList<>();
            List<Point> firstLine = pointList.subList(0, index + 1);
            List<Point> lastLine = pointList.subList(index, pointList.size());
            ramerDouglasPeucker(firstLine, epsilon, recResults1);
            ramerDouglasPeucker(lastLine, epsilon, recResults2);

            
            out.addAll(recResults1.subList(0, recResults1.size() - 1));
            out.addAll(recResults2);
            if (out.size() < 2) throw new RuntimeException("Problem assembling output");
        } else {
            
            out.clear();
            out.add(pointList.get(0));
            out.add(pointList.get(pointList.size() - 1));
        }
    }

    public static void main(String[] args) {
        List<Point> pointList = List.of(
                new Point(0.0, 0.0),
                new Point(1.0, 0.1),
                new Point(2.0, -0.1),
                new Point(3.0, 5.0),
                new Point(4.0, 6.0),
                new Point(5.0, 7.0),
                new Point(6.0, 8.1),
                new Point(7.0, 9.0),
                new Point(8.0, 9.0),
                new Point(9.0, 9.0)
        );
        List<Point> pointListOut = new ArrayList<>();
        ramerDouglasPeucker(pointList, 1.0, pointListOut);
        System.out.println("Points remaining after simplification:");
        pointListOut.forEach(System.out::println);
    }
}