Using Bluetooth GPS
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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();
TPtrC8 Lat();
TPtrC8 Lon();
TInt speed, heading;
private:
TBool Active;
TBuf8<32> lat, lon;
TBuf8<256> line;
TBuf8<32> data;
TBuf8<64> gpsid;
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 °, 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();
}
}
TPtrC8 GPS::Lat()
{
return lat;
}
TPtrC8 GPS::Lon()
{
return lon;
}
28 Sep
2009
This article represents code snippest, which gives longitude, lattitude, heading and speed information using Bluetooth GPS device. The demostrated example uses the RFCOMM transport protocol for communication. The function is performed asynchronously with the use of Active objects. The article also lucidly explains the use of socket API in the code snippest for beginners .
The code snippest presented for using Bluetooth GPS is simple and can be useful to beginners who intend to use use this feature in their application.