Question

我正在用C ++开发代码来处理我的GPS。 GPS通过UBX协议进行通信。我知道这个数据表中的消息格式。我有些怎么不能用C ++编写它。有人能告诉我一个如何用C ++编写消息/包的例子吗？

我希望从此代码获得的是纬度经度和海拔高度，但是存在一个问题，即代码不会进入切换条件，可能是因为数据不等于0xB5。有人可以告诉我我错过了什么吗？

int decode_gps() {
        while(1) {
     //  write(fd,bytestosend,6);
     //  cout<<"bytes sent = "<<bytestosend<<endl;
  read(fd,&UBX_buffer,40);

 switch(UBX_step)     //we start from zero and increment as we go through the cases
  {
  case 0:  
if(UBX_buffer[1]==0xB5)  UBX_step++;  break; // UBX sync char 1 //check for the first data packet and go to next byte


  case 1:  if(UBX_buffer[2]==0x62) UBX_step++;// UBX sync char 2 //check for the second data packet and go to the next byte

else    UBX_step=0; break;  //if first and second packets are not correct then go back and check again     

  case 2:   UBX_class=UBX_buffer[3]; checksum(UBX_class); UBX_step++;  break;

  case 3:   UBX_id=UBX_buffer[4];  checksum(UBX_id);  UBX_step++; break;

  case 4:   UBX_payload_length_hi=UBX_buffer[5]; checksum(UBX_payload_length_hi);  UBX_step++;  break;

  case 5:   UBX_payload_length_lo=UBX_buffer[6]; checksum(UBX_payload_length_lo);  UBX_step++; break;

  case 6:         // Payload data read...
  if (UBX_payload_counter < UBX_payload_length_hi)  // We stay in this state until we reach the payload_length
{
  UBX_buffer[UBX_payload_counter] = data;
  checksum(data);
  UBX_payload_counter++;
}
else
  UBX_step++; 
break;
  case 7:   ck_a=data;  UBX_step++; break;      // First checksum byte
  case 8:   ck_b=data;                           // Second checksum byte

// We end the GPS read...

if((ck_a= ck_a)&&(ck_b= ck_a))   // Verify the received checksum with the generated checksum.. 
     parse_ubx_gps();               // Parse new GPS packet...


UBX_step=0;
UBX_payload_counter=0;
ck_a=0;
ck_b=0;
GPS_timer=0; //Restarting timer...
break;
  } // End Switch 
 }
 return(0);

  } 
void parse_ubx_gps(void)
{
int j;

if(UBX_class == 0x01)
{
switch(UBX_id)
{
case 0x02: // ID NAV - POSLLH
j = 4;
lon = (float)join_4_bytes(&UBX_buffer[j]); // lon * 10000000
j += 4;
lat = (float)join_4_bytes(&UBX_buffer[j]); // lat * 10000000
j += 4;
      //Altitude = join_4_bytes(&UBX_buffer[j]); // elipsoid heigth mm
j += 4;
alt = (float)join_4_bytes(&UBX_buffer[j]); // MSL heigth mm
alt /= 10.;  

} // close case
} // if
}

UBX消息格式

0 个答案: