GPS定位发展很快，随着物联网的推广，衍生出很多GPS相关的应用万变不离其宗，主要应用的技术是GPS信号的采集、解析、将GPS信号通过4G或GPRS等传至服务器，客户端与服务器通信，获取设备位置信息，实现定位轨迹跟踪等。大概都包含这三大部分，设备、服务器后台、客户端。
设备如下
C#编写服务器后台
C#客户端
下面逐个介绍
设备采用STM32串口接收GPS模块输出的位置信息，解析出经纬度，通过AT指令控制GPRS模块与服务器通信。硬件电路如下
单片机解析GPS模块的位置信息，一般解析GPRMC这一条就可以，解析的方法很多，可以用找字头，数逗号的方式例如下面的信息。
$GPRMC,092927.000,A,2235.9058,N,11400.0518,E,0.000,74.11,151216,,D*49
$GPVTG,74.11,T,,M,0.000,N,0.000,K,D*0B
$GPGGA,092927.000,2235.9058,N,11400.0518,E,2,9,1.03,53.1,M,-2.4,M,0.0,0*6B
$GPGSA,A,3,29,18,12,25,10,193,32,14,31,,,,1.34,1.03,0.85*31
$GPGSV,3,1,12,10,77,192,17,25,59,077,42,32,51,359,39,193,49,157,36*48
$GPGSV,3,2,12,31,47,274,25,50,46,122,37,18,45,158,37,14,36,326,18*70
$GPGSV,3,3,12,12,24,045,45,26,17,200,18,29,07,128,38,21,02,174,*79
char *gpsdata;
int i,count;
if(USART_GetITStatus(USART2,USART_IT_IDLE) == SET)
{
USART2->SR;
USART2->DR;
USART_ClearITPendingBit(USART2,USART_IT_IDLE);
DMA_Cmd(DMA1_Channel6,DISABLE); //??DMA
U2_Rx_Counter = 1024 - DMA_GetCurrDataCounter(DMA1_Channel6); //??????????
gpsdata = strstr(U2_RX_data,"$GNRMC");
if(gpsdata)
{
for(i=0;i<strlen(gpsdata);i++)
{
if(gpsdata[i]==',')
{
count++;
if(count==2)
{
if(gpsdata[i+1]=='A')
{
gps_flag=1;
}
else
{
gps_n=0;
gps_e=0;
break;
}
}
if(gps_flag==1)
{
if((count==3)&&(gpsdata[i+1]!=','))
{
gps_n=((gpsdata[i+1]-0x30)*100000+(gpsdata[i+2]-0x30)*10000+((gpsdata[i+3]-0x30)*100000+(gpsdata[i+4]-0x30)*10000+(gpsdata[i+6]-0x30)*1000+(gpsdata[i+7]-0x30)*100+(gpsdata[i+8]-0x30)*10+(gpsdata[i+9]-0x30))/60);
}
if((count==5)&&(gpsdata[i+1]!=','))
{
gps_e=((gpsdata[i+1]-0x30)*1000000+(gpsdata[i+2]-0x30)*100000+(gpsdata[i+3]-0x30)*10000+((gpsdata[i+4]-0x30)*100000+(gpsdata[i+5]-0x30)*10000+(gpsdata[i+7]-0x30)*1000+(gpsdata[i+8]-0x30)*100+(gpsdata[i+9]-0x30)*10+(gpsdata[i+10]-0x30))/60);
}
if(count>=13)
{
count=0;
gps_flag=0;
break;
}
}
}
}
}
memset(U2_RX_data,0, 1024);
DMA1_Channel6->CNDTR = 1024; //??????????
DMA_Cmd(DMA1_Channel6,ENABLE); //??DMA
}单片机与服务器通过AT指令控制GPRS模块与服务器通信，AT指令是比较难的，开发过的会有感受，AT指令返回的状态比较多，并不是返回一种或两种结果。不但要按照正常流程一步一步发送AT指令，还要有错误返回处理。AT指令挺复杂的，特别适合用状态机处理这些流程。
switch (M26_info.state)
{
case GPRS_state_Poweroff :
if(AT_Delay_Timer>5)
{
GPIO_WriteBit(GPIOC, GPIO_Pin_14, Bit_SET);
GPIO_SetBits(GPIOA,GPIO_Pin_1);
GPIO_ResetBits(GPIOA, GPIO_Pin_7);
GPIO_ResetBits(GPIOA, GPIO_Pin_4); // Sleep
}
if(AT_Delay_Timer>25)
{
GPIO_ResetBits(GPIOA,GPIO_Pin_1);
GPIO_SetBits(GPIOA, GPIO_Pin_7);
}
if(AT_Delay_Timer>45)
{
GPIO_WriteBit(GPIOC, GPIO_Pin_14, Bit_RESET);
M26_info.state=GPRS_state_AT;
AT_Timeslimite=0;
AT_Delay_Timer=0;
AT_overtime=0;
ZC_DATA_flog=1;
}
break;
case GPRS_state_AT :
M26_ATTR(5,30,50,"AT+IPR=115200&W\r\n","OK","","","","",GPRS_state_CREG,GPRS_state_AT);
break;
case GPRS_state_CREG :
M26_ATTR(5,30,100,"AT+CREG?\r\n","+CREG: 0,1","+CREG: 0,5","+CREG: 0,2","+CREG: 0,3","+CREG: 0,4",GPRS_state_CSQ,GPRS_state_CREG);
break;
case GPRS_state_CSQ :
M26_ATTR(2,30,20,"AT+CSQ\r\n","+CSQ:","","","","",GPRS_state_QIDNSIP,GPRS_state_CSQ);
case GPRS_state_QIDNSIP:
M26_ATTR(2,30,5,"AT+QIFGCNT=0\r\n","OK","","","","",GPRS_state_QIDEACT,GPRS_state_Poweroff);
break;
case GPRS_state_QIDEACT:
M26_ATTR(2,2,50,"AT+QICSGP=1,\"CMMTM\"\r\n","OK","","ERROR","","",GPRS_state_QIREGAPP,GPRS_state_Poweroff);
break;
case GPRS_state_QIREGAPP:
M26_ATTR(2,2,50,"AT+QIREGAPP\r\n","OK","","ERROR","","",GPRS_state_QIACT,GPRS_state_Poweroff);
break;
case GPRS_state_QIACT:
M26_ATTR(10,2,300,"AT+QIACT\r\n","OK","","ERROR","","",GPRS_state_QIOPEN,GPRS_state_Poweroff);
break;
case GPRS_state_QIOPEN:
M26_ATTR(20,10,50,"AT+QIOPEN=\"TCP\",\"122.51.33.246\",\"8888\"\r\n","CONNECT OK","ALREADY CONNECT","ERROR","CONNECT FAIL","",GPRS_state_QISEND,GPRS_state_QIACT);
break;
case GPRS_state_QISTAT:
M26_ATTR(10,10,500,"AT+QISTAT\r\n","STATE: CONNECT OK","","STATE: IP INITIAL","","",GPRS_state_QISEND,GPRS_state_QIOPEN);
break;
case GPRS_state_QISEND:
////GPRS_DATA_flog=1;
M26_ATTR(50,20,100,"AT+QISEND=27\r\n",">",">","ERROR","ERROR","ERROR",GPRS_state_QISENDDATA,GPRS_state_QISENDDATA);
break;
case GPRS_state_QISENDDATA:
M26_senddata(10,10,100,"12345678","SEND OK","","ERROR","ERROR","ERROR",GPRS_state_QISEND,GPRS_state_Poweroff);
break;
default: ;
}服务器后台
用C#编写服务器后台程序，他负责接收所有设备发来数据，把与客户端有关的设备数据转发给客户端。这样局域网里的客户端可以通过网关获取服务器的数据。服务器程序用到多线程技术，可以同时处理多个设备发来的数据。用到了Dictionary数据类型，实现设备ID与socket对应，关键代码如下
private void ReceiveClient(object obj)
{
Socket _ClientSocket = (Socket)obj;
while (true)
{
try
{
byte[] result = new byte[1024];
int receiveLength = _ClientSocket.Receive(result);
string clientMessage = Encoding.UTF8.GetString(result, 0, receiveLength);
string Destination_Address;
string Data_Rcve;
if (receiveLength == 0)
{
ClientSocketDictionary.Remove(_ClientSocket);
_ClientSocket.Shutdown(SocketShutdown.Both);
_ClientSocket.Close();
SetText2box();
break;
}
else
{
if ((result[0] == '$') && (result[1] == '2'))//发送数据 目的地址
{
Destination_Address = clientMessage.Substring(2, 10);
Data_Rcve = clientMessage.Substring(12, clientMessage.Length-12);
temp = DateTime.Now.ToString()+ " Dest is : " + Destination_Address + " Data is : " + Data_Rcve;
SetTextbox();
SendMessage(clientMessage);
}
if ((result[0] == '$') && (result[1] == '1'))//注册ID 源地址
{
if (!ClientSocketDictionary.ContainsKey(_ClientSocket))
{
ClientSocketDictionary.Add(_ClientSocket, clientMessage.Substring(2, 10));
SetText2box();
}
else
{
ClientSocketDictionary.Remove(_ClientSocket);
ClientSocketDictionary.Add(_ClientSocket, clientMessage.Substring(2, 10));
SetText2box();
}
}
}
}
catch (Exception e)
{
ClientSocketDictionary.Remove(_ClientSocket);
_ClientSocket.Shutdown(SocketShutdown.Both);
_ClientSocket.Close();
SetText2box();
SetText3box(e);
break;
}
}
}
public void SendMessage(string msg)
{
if (msg == string.Empty || this.ClientSocketDictionary.Count <= 0) return;
string Destination_Address = msg.Substring(2, 10);
string Data_Rcve = msg.Substring(12, msg.Length-12);
msg = "$3" + Destination_Address + Data_Rcve;
try
{
foreach (KeyValuePair<Socket, string> kvp in ClientSocketDictionary)
{
if(kvp.Value.Substring(0,10)== Destination_Address)
{
kvp.Key.Send(Encoding.UTF8.GetBytes(msg));
}
}
}
catch (Exception e)
{
SetText3box(e);
}
} 客户端
C#编写客户端程序，调用百度地图API，实现地图打标，绘制轨迹。客户端工作流程是这样的，首先向服务器发送注册自身ID，然后向服务器获取相关设备ID的数据，解析数据，调用百度地图API实现打标定位等。关键代码如下
private void button1_Click(object sender, EventArgs e)
{
try
{
clientScoket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
clientScoket.Connect(new IPEndPoint(IPAddress.Parse(textBox1.Text.ToString()), 8888));
t = new Thread(ReceiveMessage);//开启线程执行循环接收消息
t.IsBackground=true;
t.Start();
button1.Text = "已连接服务器";
button1.Enabled = false;
}
catch (Exception ex)
{
SetText3box(ex);
button1.Text = "无法连接服务器";
button1.Enabled = true;
}
}
public delegate void CallSetTextbox(string ms);
void ReceiveMessage()//接收消息
{
string Destination_Address;
string Data_Rcve;
send_flog = 1;
while (true)
{
if (clientScoket.Connected == true)
{
if (send_flog == 1)
{
send_flog = 0;
message = "$1" + textBox4.Text;
SendMessage(message);
}
int length = 0;
try
{
length = clientScoket.Receive(data);
}
catch (Exception e)
{
SetText3box(e);
break;
}
if (length != 0)
{
message = Encoding.UTF8.GetString(data, 0, length);
if ((data[0] == '$') && (data[1] == '3'))//配置ID
{
Destination_Address = message.Substring(2, 10);
Data_Rcve = message.Substring(12, message.Length - 12);
Longitude = Data_Rcve.Substring(0, 8);
Latitude = Data_Rcve.Substring(8, 7);
if ((Longitude != "000.0000") && (Latitude != "00.0000"))
{
SetTextbox(DateTime.Now.ToString() + " Dest is : " + Destination_Address + " Data is : " + Data_Rcve);
}
SetText2box(DateTime.Now.ToString() + " Dest is : " + Destination_Address + " Data is : " + Data_Rcve);
}
}
}
else
{
break;
}
}