地球上兩點之間的距離計算（java）

package com.xagis.model;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class Utils {
	public static  String BLANK= "";
	public static  String ZERO= "0";
	private static  double EARTH_RADIUS = 6378.137;
	/**
	 * VincentyConstants
	 * Constants for Vincenty functions.
	 */
	public static double vincentyConstantA = 6378137;
	public static double vincentyConstantB = 6356752.3142;
	public static double vincentyConstantF = 1/298.257223563;
	
	public static void writeTextFile(String content, String path)
			throws IOException {
		BufferedWriter bw = new BufferedWriter(new FileWriter(path));
		bw.write(content);
		bw.flush();
		bw.close();
		System.out.println("文件生成成功,生成目錄:"+path);
	}

	public static String getASType(String javaType) {
		if (javaType.equals("List")) {
			return "ArrayCollection";
		}
		if (javaType.equals("boolean")) {
			return "Boolean";
		}
		return javaType;
	}

	public static String lowerCaseFirstChar(String str) {
		char[] c = str.toCharArray();
		if (c[0] >= 'A' && c[0] <= 'Z') {
			c[0] = (char) (c[0] + ('a' - 'A'));
			str = new String(c);
		}
		return str;
	}

	public static String upperCaseFirstChar(String str) {
		char[] c = str.toCharArray();
		if (c[0] >= 'a' && c[0] <= 'z') {
			c[0] = (char) (c[0] + ('A' - 'a'));
			str = new String(c);
		}
		return str;
	}

	public static String getServiceName(String methodName) {
		if (methodName.startsWith("get")) {
			return methodName.substring(3);
		} else if (methodName.startsWith("adminGet")) {
			return "Admin" + methodName.substring(8);
		} else {
			return null;
		}
	}
	//根據兩個點座標計算它們之間的距離（按照圓球體計算，粗略計算）
	public static double getDistance(double y1, double x1, double y2, double x2)
	{
		double rady1 = rad(y1);
		double rady2 = rad(y2);
		double a = rady1 - rady2;
		double b = rad(x1)-rad(x2);
		double s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a/2),2)+Math.cos(rady1)*Math.cos(rady2)*Math.pow(Math.sin(b/2),2)));
		s = s * EARTH_RADIUS;
		s = (double) (Math.round(s * 10000) / 10000);
		return s;
	}
	
	//轉換弧度
	private static double rad(double d)
	{
		return d*Math.PI/180.0;
	}
	
	/**
	 * Given two objects representing points with geographic coordinates, this
	 *     calculates the distance between those points on the surface of an
	 *     ellipsoid. 按照橢球體計算，精確計算
	 *
	 * Returns:
	 * The distance (in km) between the two input points as measured on an
	 *     ellipsoid.  Note that the input point objects must be in geographic
	 *     coordinates (decimal degrees) and the return distance is in kilometers.
	 */
	public static double distVincenty(double y1, double x1, double y2, double x2)
	{
		double a = vincentyConstantA;
		double b = vincentyConstantB; 
		double f = vincentyConstantF;
		
		double L = degtoRad(x2 - x1);
		double U1 = Math.atan((1-f) * Math.tan(degtoRad(y1)));
		double U2 = Math.atan((1-f) * Math.tan(degtoRad(y2)));
		double sinU1 = Math.sin(U1);
		double cosU1 = Math.cos(U1);
		double sinU2 = Math.sin(U2);
		double cosU2 = Math.cos(U2);
		double lambda = L;
		double lambdaP = 2*Math.PI;
		double iterLimit = 20;
		
		double sinLambda = 0.0d;
		double cosLambda = 0.0d;
		double sinSigma = 0.0d;
		double cosSigma = 0.0d;
		double sigma = 0.0d;
		double alpha = 0.0d;
		double cosSqAlpha = 0.0d;
		double cos2SigmaM = 0.0d;
		double C = 0.0d;
		
		while (Math.abs(lambda-lambdaP) > 1e-12 && --iterLimit>0) {
			 sinLambda = Math.sin(lambda);
			 cosLambda = Math.cos(lambda);
			 sinSigma = Math.sqrt((cosU2*sinLambda) * (cosU2*sinLambda) +
				(cosU1*sinU2-sinU1*cosU2*cosLambda) * (cosU1*sinU2-sinU1*cosU2*cosLambda));
			if (sinSigma==0) {
				return 0;  // co-incident points
			}
			 cosSigma = sinU1*sinU2 + cosU1*cosU2*cosLambda;
			 sigma = Math.atan2(sinSigma, cosSigma);
			 alpha = Math.asin(cosU1 * cosU2 * sinLambda / sinSigma);
			 cosSqAlpha = Math.cos(alpha) * Math.cos(alpha);
			 cos2SigmaM = cosSigma - 2*sinU1*sinU2/cosSqAlpha;
			 C = f/16*cosSqAlpha*(4+f*(4-3*cosSqAlpha));
			lambdaP = lambda;
			lambda = L + (1-C) * f * Math.sin(alpha) *
				(sigma + C*sinSigma*(cos2SigmaM+C*cosSigma*(-1+2*cos2SigmaM*cos2SigmaM)));
		}
		if (iterLimit==0) {
			return 0.0;  // formula failed to converge
		}
		double uSq = cosSqAlpha * (a*a - b*b) / (b*b);
		double A = 1 + uSq/16384*(4096+uSq*(-768+uSq*(320-175*uSq)));
		double B = uSq/1024 * (256+uSq*(-128+uSq*(74-47*uSq)));
		double deltaSigma = B*sinSigma*(cos2SigmaM+B/4*(cosSigma*(-1+2*cos2SigmaM*cos2SigmaM)-
			B/6*cos2SigmaM*(-3+4*sinSigma*sinSigma)*(-3+4*cos2SigmaM*cos2SigmaM)));
		double s = b*A*(sigma-deltaSigma);
//		double d = Number(s.toFixed(3))/1000; // round to 1mm precision
		double d = s/1000; // round to 1mm precision
		return d;
	}
	
	/**
	 * Convert degrees to radian
	 *
	 * @param val Value to convert 
	 */
	public static double degtoRad(double val){
		return val*Math.PI/180;
	}
}