using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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using System.Threading.Tasks;
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namespace Infrastructure.Service.Helper
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{
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public class CalculatedDistance
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{
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private static double HaverSin(double theta)
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{
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var v = Math.Sin(theta / 2);
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return v * v;
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}
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static double EARTH_RADIUS = 6371.0;//km 地球半径 平均值，千米
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/// <summary>
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/// 给定的经度1，纬度1；经度2，纬度2. 计算2个经纬度之间的距离。
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/// </summary>
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/// <param name="lat1">经度1</param>
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/// <param name="lon1">纬度1</param>
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/// <param name="lat2">经度2</param>
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/// <param name="lon2">纬度2</param>
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/// <returns>距离（公里、千米）</returns>
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public static int Distance(double lat1, double lon1, double lat2, double lon2)
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{
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//用haversine公式计算球面两点间的距离。
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//经纬度转换成弧度
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lat1 = ConvertDegreesToRadians(lat1);
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lon1 = ConvertDegreesToRadians(lon1);
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lat2 = ConvertDegreesToRadians(lat2);
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lon2 = ConvertDegreesToRadians(lon2);
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//差值
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var vLon = Math.Abs(lon1 - lon2);
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var vLat = Math.Abs(lat1 - lat2);
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//h is the great circle distance in radians, great circle就是一个球体上的切面，它的圆心即是球心的一个周长最大的圆。
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var h = HaverSin(vLat) + Math.Cos(lat1) * Math.Cos(lat2) * HaverSin(vLon);
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var distance = (int)((2 * EARTH_RADIUS * Math.Asin(Math.Sqrt(h))) * 1000);
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return distance;
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}
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/// <summary>
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/// 将角度换算为弧度。
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/// </summary>
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/// <param name="degrees">角度</param>
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/// <returns>弧度</returns>
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private static double ConvertDegreesToRadians(double degrees)
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{
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return degrees * Math.PI / 180;
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}
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private static double ConvertRadiansToDegrees(double radian)
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{
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return radian * 180.0 / Math.PI;
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}
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}
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}
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