(Geometry: great circle distance) The great circle distance is the distance between two points on the surface of a sphere

/*
(Geometry: great circle distance) The great circle distance is the distance between
two points on the surface of a sphere. Let (x1, y1) and (x2, y2) be the geographical
latitude and longitude of two points. The great circle distance between the two
points can be computed using the following formula:

d = radius * arccos(sin(x1) * sin(x2) + cos(x1) * cos(x2) * cos(y1 - y2))

Write a program that prompts the user to enter the latitude and longitude of two
points on the earth in degrees and displays its great circle distance. The average
earth radius is 6,371.01 km. Note that you need to convert the degrees into radians
using the Math.toRadians method since the Java trigonometric methods use
radians. The latitude and longitude degrees in the formula are for north and west.
Use negative to indicate south and east degrees.
*/
import java.util.Scanner;

public class Exercise_04_02 {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);

		final double RADIUS = 6371.01;	// Constant value

		// Prompt the user to enter the latitude and longitude
		// of two points on the earth in degrees
		System.out.print("Enter point 1 (latitude and longitude) in degrees: ");
		String xy1 = input.nextLine();
		System.out.print("Enter point 2 (latitude and longitude) in degrees: ");
		String xy2 = input.nextLine();

		// Extract x and y values from string
		int k = xy1.indexOf(',');
		double x1 = Double.parseDouble(xy1.substring(0, k - 1));
		double y1 = Double.parseDouble(xy1.substring(k + 2));
		k = xy2.indexOf(',');
		double x2 = Double.parseDouble(xy2.substring(0, k - 1));
		double y2 = Double.parseDouble(xy2.substring(k + 2));

		// Convert degrees to radians
		x1 = Math.toRadians(x1);
		y1 = Math.toRadians(y1);
		x2 = Math.toRadians(x2);
		y2 = Math.toRadians(y2);

		// Calculate its great circle distance
		double distance = 
			RADIUS * Math.acos(Math.sin(x1) * Math.sin(x2) + 
			Math.cos(x1) * Math.cos(x2) * Math.cos(y1 - y2));

		// Display result
		System.out.println("The distance between the two points is " + distance);
	}
}