測試了一共八組點，大概關係是這樣的

計算的是那八個點從正北方向按順時針轉過的角度的大小

#include "stdafx.h"
#include <math.h>
#include <iostream>
#include <stdio.h>
#define PI                      3.141592654
#define EARTH_RADIUS            6378.137        //地球近似半徑
using namespace std;
double get_distance(double lat1, double lng1, double lat2, double lng2);
int get_angle(double lat1, double lng1, double lat2, double lng2);
int _tmain(int argc, _TCHAR* argv[])
{
	int anglee1 = get_angle(39.9465141, 116.906654, 39.945908, 116.906084);//1
	cout << anglee1 << endl;
	int anglee2 = get_angle(39.9459305, 116.906914, 39.945908, 116.906084);//2
	cout << anglee2<< endl;
	int anglee3 = get_angle(39.9453354, 116.906685, 39.945908, 116.906084);//3
	cout << anglee3 << endl;
	int anglee4 = get_angle(39.945076, 116.906105, 39.945908, 116.906084);//4
	cout << anglee4 << endl;
	int anglee5 = get_angle(39.9453049, 116.90551, 39.945908, 116.906084);//5
	cout << anglee5 << endl;
	int anglee6 = get_angle(39.9458847, 116.905251, 39.945908, 116.906084);//6
	cout << anglee6 << endl;
	int anglee7= get_angle(39.9464798, 116.905479, 39.945908, 116.906084);//7
	cout << anglee7 << endl;
	int anglee8 = get_angle(39.9467392, 116.906059, 39.945908, 116.906084);//8
	cout << anglee8 << endl;
	return 0;
}

//兩點的距離（緯度，經度）
double get_distance(double lat1, double lng1, double lat2, double lng2)
{
	double radLat1 = lat1 * PI / 180.0;   //角度1˚ = π / 180
	double radLat2 = lat2 * PI / 180.0;   //角度1˚ = π / 180
	double a = radLat1 - radLat2;//緯度之差
	double b = lng1 * PI / 180.0 - lng2* PI / 180.0;  //經度之差
	double dst = 2 * asin((sqrt(pow(sin(a / 2), 2) + cos(radLat1) * cos(radLat2) * pow(sin(b / 2), 2))));
	dst = dst * EARTH_RADIUS;
	dst = round(dst * 10000) / 10000;
	return dst;
}

//計算角度
int get_angle(double lat1, double lng1, double lat2, double lng2)
{
	double x = lat1 - lat2;//t d
	double y = lng1 - lng2;//z y
	int angle=-1;
	if (y == 0 && x > 0) angle = 0;
	if (y == 0 && x < 0) angle = 180;
	if(x ==0 && y > 0) angle = 90;
	if(x == 0 && y < 0) angle = 270;
	if (angle == -1)
	{
		double dislat = get_distance(lat1, lng2, lat2, lng2);
		double dislng = get_distance(lat2, lng1, lat2, lng2);
		if (x > 0 && y > 0) angle = atan2(dislng, dislat) / PI * 180;
		if (x < 0 && y > 0) angle = atan2(dislat, dislng) / PI * 180+90;
		if (x < 0 && y < 0) angle = atan2(dislng, dislat) / PI * 180 + 180;
		if (x > 0 && y < 0) angle = atan2(dislat, dislng) / PI * 180 + 270;
	}
	return angle;
}