C 简单实现LBS基站定位
C 简单实现LBS基站定位<div id="cnblogs_post_body"> 目前移动设备定位基本使用GPS的定位方式，使用基站定位的比较少，但是有些设备对定位要求不是很高或者需要节省掉gps芯片带来的成本，那么就可以考虑使用基站定位了。
基站定位的原理很简单：就是访问Google服务器，告诉它我们的基站信息，服务器就会返回经纬度信息实现定位。那么我们只要知道基站信息是由什么组成的、如何组织Google服务器需要的基站信息，然后发送给Google服务器就好了。
基站信息简单的说是由LAI(Location Area Identification) + CID(Cell Identity)组成的, LAI由(MCC +MNC+LAC)组成其中MCC全名Mobile Country Code，移动国家码，三位数，如中国为460。MNC全名Mobile Network Code，移动网络号，两位数。LAC全名Location Area Code，是一个2个字节长的十六进制BCD码(不包括0000和FFFE)。Cell Identity 小区码，同样是2个字节长的十六进制BCD码。我们只需要知道LAC和CID就可以完成定位。
组消息发送给Google服务器时应注意要使用POST的方式向www.google.com/glm/mmap 提交请求内容，内容类型必须是Binary，其次内容格式是必须按照google规定的方式填充没什么好说的，注意网络字节序即可。
在获取Google服务器返回的内容时，offset=7后的4个字节是latitude，offset=11后4个字节是longitude。
下面是用C语言实现只依赖于C库很方便移植，本人在ARM平台及X86 linux下均测可用，同样可用于Android JNI。
<div class="cnblogs_Highlighter">/* * Copyright(c) 2010-2015 Beck. All rights reserved. * * Function : get latitude and longitude using cell identity and location area code * Author : Beck <becklc@163.com> **/#include <stdio.h>#include <string.h>#include <netdb.h>#include <errno.h>#include <sys/socket.h>#define HOSTNAME "www.google.com"#define RequestHttpHeader "POST /glm/mmap HTTP/1.1\x0D\x0A"\ "Content-Type: application/binary\x0D\x0A"\ "Host: www.google.com\x0D\x0A"\ "Content-Length: 55\x0D\x0A"\ "Expect: 100-continue\x0D\x0A"\ "Connection: Close\x0D\x0A\x0D\x0A"#define ContentLenFlag "\x0D\x0A""Content-Length:\x20"#define SIZE_REQDATA 55typedef struct { uint32_t cti; /* Cell Identity */ uint32_t lac; /* Location Area Code */ uint32_t mcc; /* Mobile Country Code */ uint32_t mnc; /* Mobile Network Code */} bsi_t;typedef struct { bsi_t bsi; uint8_t reqdata; double latitude; double longitude;} infos_t;static infos_t infos;int is_little_endian(){ int i = 1; return (*(char *) &i == 1) ? 1 : 0;}static char *str2hex(const char *src, char *dec, int len){ char *hex = "0123456789ABCDEF"; char *ret = dec; int i = 0; if (NULL == src || NULL == dec) return NULL; for (i = 0; i < len; i++) { *ret++ = hex[((*(src + i) & 0xF0) >> 4) & 0x0F]; *ret++ = hex[*(src + i) & 0x0F]; *ret++ = ' '; } return ret = dec;}static int connect_to_server(const char *strhost, uint16_t port){ struct hostent *host; struct sockaddr_in serv_addr; int hsocket = -1; if ((host = gethostbyname(strhost)) == NULL) { printf("%s, gethostbyname error, %s\n", __func__, strerror(errno)); return -1; } if ((hsocket = socket(AF_INET, SOCK_STREAM, 0)) == -1) { printf("%s, socket error, %s\n", __func__, strerror(errno)); return -1; } serv_addr.sin_family = AF_INET; serv_addr.sin_port = htons(port); serv_addr.sin_addr = *((struct in_addr *) host->h_addr); memset(&(serv_addr.sin_zero), 0x0, 8); if (connect(hsocket, (struct sockaddr *) &serv_addr, sizeof(struct sockaddr)) == -1) { printf("%s, connect error, %s\n", __func__, strerror(errno)); return -1; } return hsocket;}/* get the size of content from HttpServer */static int get_content_size(const char *recvdata, int recvdatalen){ /* check status is ok */ char *pok = NULL; char *p = NULL, *end = NULL; int value = 0, valuelen = 0, c; if (NULL == (pok = strstr(recvdata, "OK"))) { printf("Not find 'OK' flag in recv data.\n"); return -1; } /* find the flag Content-Length: in recvdata */ if (NULL == (p = strstr(recvdata, ContentLenFlag))) { printf("Not find 'Content_Length' flag in recv data.\n"); return -1; } p = p + sizeof(ContentLenFlag) - 1; /* find the end of Content-Length: */ if (NULL == (end = strstr(p, "\x0D\x0A"))) { printf("Not find the end of 'Content_Length' in recv data.\n"); return -1; } /* str2int */ value = 0; valuelen = end - p; for (; valuelen > 0; valuelen--) { if ((c = *p++ - '0') >= 10) return -1; value = value * 10 + c; } /* check the third number in content is 0x00 */ if (0x00 != recvdata) { printf("the content in recv data is invalid.\n"); return -1; } return value;}static double getdata(uint8_t * pdata, int pos){ if (NULL == pdata) return -1; if (is_little_endian()) { return ((double)((pdata << 24) | (pdata << 16) | (pdata << 8) | (pdata))) / 1000000; } else { return ((double) (*(uint32_t *) & pdata)) / 1000000; }}static int get_latitude_longitude(infos_t * p){ int hsocket = -1; int pos = 0, len = 0, ret = 0; int contentSize = 0; char recvRsp = { 0 }; if ((hsocket = connect_to_server(HOSTNAME, 80)) == -1) { printf("%s, connect to server error, %s\n", __func__, strerror(errno)); ret = -1; goto err; } if (-1 == send(hsocket, RequestHttpHeader, strlen(RequestHttpHeader), 0)) { printf("%s, send RequestHttpHeader error, %s\n", __func__, strerror(errno)); ret = -1; goto err; } if (-1 == send(hsocket, p->reqdata, SIZE_REQDATA, 0)) { printf("%s, send reqdata error, %s\n", __func__, strerror(errno)); ret = -1; goto err; } while ((pos = recv(hsocket, recvRsp + len, sizeof(recvRsp) - len, 0)) > 0) { len += pos; } contentSize = get_content_size(recvRsp, len); p->latitude = getdata((uint8_t *) (recvRsp + len - contentSize), 7); p->longitude = getdata((uint8_t *) (recvRsp + len - contentSize), 11);err: close(hsocket); return ret;}static int reqdata_init(infos_t * p){ p->reqdata= 0x0e; p->reqdata = 0x1b; /* wcdma unsame to gsm */ p->reqdata = ((uint64_t) p->bsi.cti > 65536) ? 5 : 3; p->bsi.cti = htonl(p->bsi.cti); p->bsi.lac = htonl(p->bsi.lac); p->bsi.mcc = htonl(p->bsi.mcc); p->bsi.mnc = htonl(p->bsi.mnc); memcpy(p->reqdata + 17, &p->bsi.mnc, 4); memcpy(p->reqdata + 21, &p->bsi.mcc, 4); memcpy(p->reqdata + 31, &p->bsi.cti, 4); memcpy(p->reqdata + 35, &p->bsi.lac, 4); memcpy(p->reqdata + 39, &p->bsi.mnc, 4); memcpy(p->reqdata + 43, &p->bsi.mcc, 4); memset(p->reqdata + 47, 0xff, 4); return 0;}int main(int argc, char *argv[]){ if (argc != 3) { printf("usage <%s> : %s <CellTowerId> <LocationAreaCode>\n", argv, argv); return 0; } infos_t *p = infos; memset(p, 0x0, sizeof(infos_t)); p->bsi.cti = (uint32_t) atoi(argv); p->bsi.lac = (uint32_t) atoi(argv); reqdata_init(p); if (0 == get_latitude_longitude(p)) { printf("latitude : %g, longitude : %g\n", p->latitude, p->longitude); } else printf("failed.\n"); return 0;}
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