C 简单实现LBS基站定位
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;
}
本文原创，欢迎转载，转载请注明出处<becklc@163.com>
