Code:
import static java.lang.Math.abs;
import static java.lang.Math.pow;
import static java.lang.Math.sqrt;
import java.util.Random;
class RamerDouglasPeuckerFilter
{
private double epsilon;
public RamerDouglasPeuckerFilter(double epsilon)
{
if (epsilon <= 0)
{
throw new IllegalArgumentException("Epsilon nust be > 0");
}
this.epsilon = epsilon;
}
public double[] filter(double[] data)
{
return ramerDouglasPeuckerFunction(data, 0, data.length - 1);
}
public double getEpsilon()
{
return epsilon;
}
protected double[] ramerDouglasPeuckerFunction(double[] points,
int startIndex, int endIndex)
{
double dmax = 0;
int idx = 0;
double a = endIndex - startIndex;
double b = points[endIndex] - points[startIndex];
double c = -(b * startIndex - a * points[startIndex]);
double norm = sqrt(pow(a, 2) + pow(b, 2));
for (int i = startIndex + 1; i < endIndex; i++)
{
double distance = abs(b * i - a * points[i] + c) / norm;
if (distance > dmax)
{
idx = i;
dmax = distance;
}
}
if (dmax >= epsilon)
{
double[] recursiveResult1 = ramerDouglasPeuckerFunction(points,
startIndex, idx);
double[] recursiveResult2 = ramerDouglasPeuckerFunction(points,
idx, endIndex);
double[] result = new double[(recursiveResult1.length - 1)
+ recursiveResult2.length];
System.arraycopy(recursiveResult1, 0, result, 0,
recursiveResult1.length - 1);
System.arraycopy(recursiveResult2, 0, result,
recursiveResult1.length - 1, recursiveResult2.length);
return result;
} else
{
return new double[] { points[startIndex], points[endIndex] };
}
}
public void setEpsilon(double epsilon)
{
if (epsilon <= 0)
{
throw new IllegalArgumentException("Epsilon nust be > 0");
}
this.epsilon = epsilon;
}
}
public class Douglas_Peucker_Algorithm
{
public static void main(String args[])
{
Random random = new Random();
double[] points = new double[20];
double[] fpoints;
for (int i = 0; i < points.length; i++)
points[i] = random.nextInt(10);
RamerDouglasPeuckerFilter rdpf = new RamerDouglasPeuckerFilter(1);
fpoints = rdpf.filter(points);
System.out.println("Orginal points");
for (int i = 0; i < points.length; i++)
System.out.print(points[i] + " ");
System.out.println("\nFiltered points");
for (int i = 0; i < fpoints.length; i++)
System.out.print(fpoints[i] + " ");
}
}
Output:
Orginal points
5.0 0.0 8.0 7.0 2.0 9.0 4.0 4.0 0.0 7.0 4.0 1.0 9.0 6.0 8.0 9.0 6.0 6.0 9.0 6.0
Filtered points
5.0 0.0 8.0 2.0 9.0 0.0 7.0 1.0 9.0 6.0 9.0 6.0 9.0 6.0
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