Categories: Symbian C++ | S60 | Code Examples | Bluetooth | GPS

This page was last modified 18:42, 9 June 2008.

From Forum Nokia Wiki

How to Use a Bluetooth GPS

The GPS class shows how to use a Bluetooth GPS device and read location information from it. It displays a selection dialog for the user and starts receiving data from the selected device. Currently it only parses the RMC message which is required in all GPS devices. This gives the latitude, longitude, heading and speed information but not altitude nor dilution.

You need to implement messaging for lost signal etc if you want to show them to the user.

You can also use the Parse() method to convert the received values to degrees, minutes and seconds as well as a combined integer value multiplied by 65536.

This example assumes that the GPS device uses RFCOMM channel 1 as data channel. This has been the case in every device I've used, so it's a safe assumption.

GPS.h

#ifndef GPS_H_
#define GPS_H_
 
#include <e32std.h>
#include <btmanclient.h>
#include <btextnotifiers.h>
#include <es_sock.h>
#include <in_sock.h>
#include <bt_sock.h>
 
class GPS : public CActive
{
public:
	GPS();
	virtual ~GPS();
	void ConstructL();
 
	void DoCancel();
	void RunL();
 
	TPtrC Lat();
	TPtrC Lon();
 
	TInt			speed, heading;
 
private:
	TBool Active;
	TBuf8<32> lat, lon;
 
	TBuf8<256> line;
	TBuf8<32> data;
	int state;
	RSocket iSendingSocket;
	RSocketServ iSocketServer;
};
 
#endif /*GPS_H_*/

GPS.cpp

#include "GPS.h"
#include <e32math.h>
 
_LIT8(ZERO, "0");
_LIT(RFCOMM, "RFCOMM");
_LIT8(KGPS, "GPS");
 
void Parse(TDesC8 &data, TInt &deg, TInt &min, TInt &sec, TInt32 &whole)
{
	TLex8 lex(data);
 
	lex.Val(deg);
	lex.Inc();
	lex.Val(min);
	sec = min * 60;
	int l = (data.Length() - data.Find(_L8(".")));
	int x = 1;
	while (l-- > 0)
		x *= 10;
	sec /= x/100;
 
	min = deg % 100;
	deg /= 100;
 
	whole = deg * 65536 + (min * 65536 / 60) + (sec * 65536 / 36000);
}
 
GPS::GPS() : CActive(EPriorityLow)
{
	state = 0;
}
 
GPS::~GPS()
{
	TRAPD(err, Cancel());
	TRAP(err, Deque());
}
 
void GPS::RunL()
{
	int i, j;
 
	if (iStatus == KErrNone)
  {
		if (state == 1)
		{
			state = 2;
			line.Zero();
			iSendingSocket.Read(data, iStatus);
			SetActive();
		}
		else if (state == 2)
		{
			int rpos = 0;
 
			while ((rpos = data.Locate('\r')) != KErrNotFound)
			{
				line.Append(data.Left(rpos));
				if (data.Length() > rpos + 2)
				{
					if (data[rpos + 1] == '\n')
						data.Copy(data.Mid(rpos+2));
					else
						data.Copy(data.Mid(rpos+1));
				}
				else
				{
					data.Zero();
				}
 
				if (line.Length() > 10)
				{
					// RMC - lat, lon, speed
					if ((line[3] == 'R') && (line[4] == 'M') && (line[5] == 'C'))
					{
						j = i = 0;
						while ((i < line.Length()) && (line[i] != ','))
							i++;
						i++;
 
						j = i;
						while ((i < line.Length()) && (line[i] != ','))
							i++;
						i++;
 
						// If there is no signal, this is not A
						if (line[i] != 'A')
						{
							lat.Copy(ZERO);
							lon.Copy(ZERO);
							latdeg = londeg = latmin = lonmin = latsec = lonsec = 0;
							line.Zero();
							iSendingSocket.Read(data, iStatus);
							SetActive();
							return;
						}
 
						while ((i < line.Length()) && (line[i] != ','))
							i++;
						i++;
						j = i;
						while ((i < line.Length()) && (line[i] != ','))
							i++;
 
						// Copy latitude from the message
						lat.Copy(line.Mid(j, i-j));
						// If it's southern hemisphere, negate the value
						if (line[i+1] == 'S')
							lat.Insert(0, _L8("-"));
 
						i += 3;
						j = i;
						while ((i < line.Length()) && (line[i] != ','))
							i++;
 
						// Copy longitude from the message
						lon.Copy(line.Mid(j, i-j));
						// If it's western hemisphere, negate the value
						if (line[i+1] == 'W')
							lon.Insert(0, _L8("-"));
 
						i += 3;
						j = i;
						while ((i < line.Length()) && (line[i] != ','))
							i++;
 
						// Read speed from the message
						TLex8 lex(line.Mid(j, i-j));
						lex.Val(speed);
						speed *= 10;
						if (lex.Peek() == '.')
						{
							lex.Inc();
							if (lex.Peek() != 0)
								speed += ((int)lex.Peek() - '0');
						}
						// Convert speed from knots to km/h
						speed *= 1852;
						speed /= 1000;
 
						i++;
						j = i;
						while ((i < line.Length()) && (line[i] != ','))
							i++;
 
						// Read heading from the message
						lex.Assign(line.Mid(j, i-j));
						lex.Val(heading);
						heading *= 10;
						// Check if it's not integer
						if (lex.Peek() == '.')
						{
							lex.Inc();
							if (lex.Peek() != 0)
								heading += ((int)lex.Peek() - '0');
						}
					}
				}
 
				line.Zero();
			}
 
			line.Append(data);
 
			iSendingSocket.Read(data, iStatus);
			SetActive();
		}
  }
	// Error occurred...
	else
	{
		lat.Copy(ZERO);
		lon.Copy(ZERO);
	}
}
 
void GPS::DoCancel()
{
	if (state > 0)
		iSendingSocket.Close();
	iSocketServer.Close();
}
 
void GPS::ConstructL()
{
	TBTDeviceResponseParamsPckg resultPckg;
 
	CActiveScheduler::Add(this);
 
	// 1. Create a notifier
	RNotifier notif;
	User::LeaveIfError(notif.Connect());
 
	if (gpsid.Length() == 0)
	{
		state = 0;
		// 2. Start the device selection plug-in
		TBTDeviceSelectionParams selectionFilter;
		TUUID targetServiceClass(0x2345);
		selectionFilter.SetUUID(targetServiceClass);
		TBTDeviceSelectionParamsPckg pckg(selectionFilter);
		TRequestStatus status;
		notif.StartNotifierAndGetResponse(status,
KDeviceSelectionNotifierUid, pckg, resultPckg);
		User::After(2000000);
 
		// 3. Extract device name if it was returned
		User::WaitForRequest(status);
 
		User::LeaveIfError(iSocketServer.Connect());
 
		if (status.Int() == KErrNone)
		{
			User::LeaveIfError(iSendingSocket.Open(iSocketServer,
RFCOMM));
			TBTSockAddr address;
			gpsid.Copy(resultPckg().BDAddr().Des());
			address.SetBTAddr(resultPckg().BDAddr());
			// GPS devices usually use port 1 as data channel
			// so we don't have to query it
			address.SetPort(1);
 
			state = 1;
			iSendingSocket.Connect(address, iStatus);
			SetActive();
		}
		else
		{
			CHainMAppView::Static()->Notification(EGPSNotFound);
		}
	}
	else
	{
		User::LeaveIfError(iSocketServer.Connect());
		User::LeaveIfError(iSendingSocket.Open(iSocketServer, RFCOMM));
 
		TBTSockAddr address;
		TBTDevAddr a(gpsid);
		address.SetBTAddr(a);
		address.SetPort(1);
 
		state = 1;
		iSendingSocket.Connect(address, iStatus);
		SetActive();
	}
}
 
TPtrC GPS::Lat()
{
	return lat;
}
 
TPtrC GPS::Lon()
{
	return lon;
}

Internal relevant link

• Bluetooth GPS Receiver - NMEA Parsing