用大圆距离公式寻找附近的出租车-yiteyi-C++库

给定需要出租车的人的GPS坐标（以度为单位），以及以JSON格式存储在文本文件中的城市所有出租车坐标，查找50公里范围内所有可用出租车司机的用户id和姓名。

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例如：

输入：记录客户。json包含需要出租车的人的GPS坐标（以度为单位），以及城市中所有出租车的坐标，以json格式存储在文本文件中。

输出：文件答案。json包含50公里范围内所有可用出租车司机的用户id和姓名，并存储在一个新文件中。

推荐：请尝试你的方法 {IDE} 首先，在进入解决方案之前。

采用的方法： 1. 以字符串格式获取每个驾驶室的纬度和经度及其 JSON编码输入文件中的用户id和名称。

2. 将以字符串格式显示的cab的纬度和经度转换为双精度。

3. 转换中存在的用户和驾驶室的纬度和经度度到弧度。

4. 使用大圆计算用户位置和驾驶室之间的距离距离公式。

5. 如果发现距离小于或等于50公里，则输出用户信息- 将出租车司机的id和姓名添加到新文件中，否则不采取任何行动。

运行程序的过程： 1.保存密码文件呢 客户。json 在同一个地方。 2.现在，编译代码（使用cmd: g++文件名。cpp )然后运行它（使用cmd: /a.外出/回家/gfg/顾客。json )通过文件名传递给客户。json以及正确的位置 （例如/home/gfg/customers.json）。 3.名为 答案。json 将在代码和客户所在的同一位置创建。json文件已存在。

                     // C++ code to find cabs nearby                   
                     #include <bits/stdc++.h>                   
                     using                               namespace                               std;                   
                             
                     // Latitude of customer who needs a cab.                   
                     #define lat1d 12.9611159                   
                             
                     // Longitude of customer who needs a cab.                   
                     #define lon1d 77.6362214                   
                             
                     #define pi 3.14159265358979323846                   
                     #define earth_radius 6371.0                   
                             
                     ifstream customer_list (                               "customers.json"                               );                   
                     ofstream out (                               "answer.json"                               );                   
                             
                     // Function to convert degree to radian.                   
                     double                               degtorad(                               double                               deg)                   
                     {                   
                                         return                               ( deg * pi / 180);                   
                     }                   
                             
                     // Function to calculate distance                   
                     // between 2 given locations                   
                     // using Great Circle Distance Formula.                   
                     double                               distanceEarth(                               double                               lat2d,                               double                               lon2d)                   
                     {                   
                                         double                               lat1, lon1, lat2, lon2,                   
                                         delta_lon, central_ang;                   
                             
                                         lat1 = degtorad(lat1d);                   
                                         lon1 = degtorad(lon1d);                   
                                         lat2 = degtorad(lat2d);                   
                                         lon2 = degtorad(lon2d);                   
                             
                                         delta_lon = lon2 - lon1;                   
                             
                                         // great circle distance formula.                   
                                         central_ang =                               acos                               (                               sin                               (lat1) *                   
                                         sin                               (lat2) +                               cos                               (lat1) *                   
                                         cos                               (lat2) *                               cos                               (delta_lon) );                   
                             
                                         return                               (earth_radius * central_ang);                   
                     }                   
                             
                     // Structure which contains data and                   
                     // functions for accessing and processing                   
                     // data from the given customers.json file.                   
                     struct                               json                   
                     {                   
                                         /* i and j are used to access various                   
                                         elements of the char arrays. x is used                   
                                         to measure the size of the element of                   
                                         latitude_as_string array. y is used to                   
                                         measure the size of the element of                   
                                         longitude_as_string array. m is used                   
                                         to measure the size of the element                   
                                         of id_as_string array. n is used to                   
                                         measure the size of the element of                   
                                         name array. f keeps count of " " "                   
                                         symbol. fi keeps count of " : " symbol.                   
                                         */                   
                                         long                               long                               int                               length, i, j, x, y, m,                   
                                         n, f, fi, id[100000];                   
                             
                                         char                               latitude_as_string[1000],                   
                                         longitude_as_string[1000],                   
                                         id_as_string[1000], name[1000];                   
                             
                                         double                               lat2d, lon2d;                   
                             
                                         // To get each line of customers.json                   
                                         // file as string.                   
                                         string line;                   
                             
                                         // Function to check whether distance between                   
                                         // 2 points is less than 50km or not.                   
                                         void                               distance_calculator()                   
                                         {                   
                                         if                               (distanceEarth(lat2d, lon2d) <= 50.0000)                   
                                         {                   
                                         // Converting id to int format.                   
                                         id[i] = atoll(id_as_string);                   
                                         i++;                   
                                         out <<                               "{"user_id": "                               << id[i - 1] <<                   
                                         ", "name": "                               << name <<                               "}"                               << endl;                   
                                         }                   
                                         }                   
                             
                                         // Function to read various attributes                   
                                         // like latitude, longitude, name , id,                   
                                         // etc, from customers.json file. simplistic                   
                                         // approach is used to get JSON attributes.                   
                                         void                               json_parser()                   
                                         {                   
                                         if                               (customer_list.is_open())                   
                                         {                   
                             
                                         while                               (getline(customer_list, line))                   
                                         {                   
                             
                                         f = 0; x = 0; y = 0; fi = 0; m = 0, n = 0;                   
                                         length = line.size();                   
                             
                                         for                               (j = 0; j < length; j++)                   
                                         {                   
                             
                                         if                               (line[j] ==                               '"'                               )                   
                                         f++;                   
                             
                                         else                               if                               (line[j] ==                               ':'                               )                   
                                         fi++;                   
                             
                                         // To get latitude of the location.                   
                                         if                               (f == 3)                   
                                         {                   
                                         j++;                   
                             
                                         while                               (line[j] !=                               '"'                               )                   
                                         {                   
                                         latitude_as_string[x] = line[j];                   
                                         x++; j++;                   
                                         }                   
                             
                                         j--; latitude_as_string[x] =                               ' '                               ;                   
                                         }                   
                             
                                         // To get longitude of the location.                   
                                         else                               if                               (f == 13)                   
                                         {                   
                                         j++;                   
                             
                                         while                               (line[j] !=                               '"'                               )                   
                                         {                   
                                         longitude_as_string[y] = line[j];                   
                                         y++; j++;                   
                                         }                   
                             
                                         j--; longitude_as_string[y] =                               ' '                               ;                   
                                         }                   
                             
                                         // To get id of the friend.                   
                                         if                               (fi == 2)                   
                                         {                   
                                         j += 2;                   
                             
                                         while                               (line[j] !=                               ','                               )                   
                                         {                   
                                         id_as_string[m] = line[j];                   
                                         m++; j++;                   
                                         }                   
                             
                                         j--; id_as_string[m] =                               ' '                               ;                   
                                         fi++;                   
                                         }                   
                             
                                         // To get name of the friend.                   
                                         else                               if                               (fi == 4)                   
                                         {                   
                                         j += 2;                   
                             
                                         while                               (line[j] !=                               ','                               )                   
                                         {                   
                                         name[n] = line[j];                   
                                         n++; j++;                   
                                         }                   
                             
                                         j--; name[n] =                               ' '                               ;                   
                                         fi++; f += 2;                   
                                         }                   
                                         }                   
                             
                                         // Converting latitude and longitude                   
                                         // in string to float.                   
                                         lat2d =                               atof                               (latitude_as_string);                   
                                         lon2d =                               atof                               (longitude_as_string);                   
                                         distance_calculator();                   
                                         }                   
                                         }                   
                             
                                         // closing stream of customer's file.                   
                                         customer_list.close();                   
                             
                                         // closing stream of answer's file.                   
                                         out.close();                   
                                         }                   
                     };                   
                             
                     int                               main()                   
                     {                   
                                         // Creating object of the structure json                   
                                         json obj;                   
                             
                                         // To read customers.json file.                   
                                         obj.json_parser();                   
                                         return                               0;                   
                     }                   

输入文件（customers.json）：

{"latitude": "12.986375", "user_id": 12, "name": "Chris", "longitude": "77.043701"}
{"latitude": "11.92893", "user_id": 1, "name": "Alice", "longitude": "78.27699"}
{"latitude": "11.8856167", "user_id": 2, "name": "Ian", "longitude": "78.4240911"}
{"latitude": "12.3191841", "user_id": 3, "name": "Jack", "longitude": "78.5072391"}
{"latitude": "13.807778", "user_id": 28, "name": "Charlie", "longitude": "76.714444"}
{"latitude": "13.4692815", "user_id": 7, "name": "Frank", "longitude": "-9.436036"}
{"latitude": "14.0894797", "user_id": 8, "name": "Eoin", "longitude": "77.18671"}
{"latitude": "13.038056", "user_id": 26, "name": "Stephen", "longitude": "76.613889"}
{"latitude": "14.1225", "user_id": 27, "name": "Enid", "longitude": "78.143333"}
{"latitude": "13.1229599", "user_id": 6, "name": "Theresa", "longitude": "77.2701202"}
{"latitude": "12.2559432", "user_id": 9, "name": "Jack", "longitude": "76.1048927"}
{"latitude": "12.240382", "user_id": 10, "name": "Georgina", "longitude": "77.972413"}
{"latitude": "13.2411022", "user_id": 4, "name": "Ian", "longitude": "77.238335"}
{"latitude": "13.1302756", "user_id": 5, "name": "Nora", "longitude": "77.2397222"}
{"latitude": "13.008769", "user_id": 11, "name": "Richard", "longitude": "77.1056711"}
{"latitude": "13.1489345", "user_id": 31, "name": "Alan", "longitude": "77.8422408"}
{"latitude": "13", "user_id": 13, "name": "Olive", "longitude": "76"}
{"latitude": "11.999447", "user_id": 14, "name": "Helen", "longitude": "-9.742744"}
{"latitude": "12.966", "user_id": 15, "name": "Michael", "longitude": "77.463"}
{"latitude": "12.366037", "user_id": 16, "name": "Ian", "longitude": "78.179118"}
{"latitude": "14.180238", "user_id": 17, "name": "Patricia", "longitude": "-5.920898"}
{"latitude": "13.0033946", "user_id": 39, "name": "Lisa", "longitude": "77.3877505"}
{"latitude": "12.228056", "user_id": 18, "name": "Bob", "longitude": "76.915833"}
{"latitude": "14.133333", "user_id": 24, "name": "Rose", "longitude": "77.433333"}
{"latitude": "55.033", "user_id": 19, "name": "Enid", "longitude": "78.112"}
{"latitude": "13.121111", "user_id": 20, "name": "Enid", "longitude": "-9.831111"}
{"latitude": "11.802", "user_id": 21, "name": "David", "longitude": "-9.442"}
{"latitude": "14.374208", "user_id": 22, "name": "Charlie", "longitude": "78.371639"}
{"latitude": "13.74412", "user_id": 29, "name": "Oliver", "longitude": "76.11167"}
{"latitude": "13.761389", "user_id": 30, "name": "Nick", "longitude": "76.2875"}
{"latitude": "14.080556", "user_id": 23, "name": "Eoin", "longitude": "77.361944"}
{"latitude": "12.833502", "user_id": 25, "name": "David", "longitude": "78.122366"}

输出文件（answers.json）：

{"user_id": 6, "name": "Theresa"}
{"user_id": 5, "name": "Nora"}
{"user_id": 31, "name": "Alan"}
{"user_id": 15, "name": "Michael"}
{"user_id": 39, "name": "Lisa"}

参考： 大圆距离

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