LBS定位实现

    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。

/*

* 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            55

typedef 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[SIZE_REQDATA];

    double latitude;

    double longitude;

} infos_t;

static infos_t infos[1];

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[recvdatalen - value + 3]) {

        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[pos] << 24) | (pdata[pos + 1] << 16) |

                (pdata[pos + 2] << 8) | (pdata[pos + 3]))) / 1000000;

    } else {

        return (( double ) (*(uint32_t *) & pdata[pos])) / 1000000;

    }

}

static int get_latitude_longitude(infos_t * p)

{

    int hsocket = -1;

    int pos = 0, len = 0, ret = 0;

    int contentSize = 0;

    char recvRsp[512] = { 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[1]  = 0x0e;

    p->reqdata[16] = 0x1b;

    /* wcdma unsame to gsm */

    p->reqdata[28] = ((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[0], argv[0]);

        return 0;

    }

    infos_t *p = infos;

    memset (p, 0x0, sizeof (infos_t));

    p->bsi.cti = (uint32_t) atoi (argv[1]);

    p->bsi.lac = (uint32_t) atoi (argv[2]);

    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;

}