Log File Position Source (C++)▲
The data is read from a file which has positional data in NMEA format. The resulting time and position information is then displayed to the screen as simple text in date/time and latitude/longitude format.
This example class reads position data from a text file, log.txt. The file specifies position data using a simple text format: it contains one position update per line, where each line contains a date/time, a latitude and a longitude, separated by spaces. The date/time is in ISO 8601 format and the latitude and longitude are in degrees decimal format. Here is an excerpt from log.txt:
2009-08-24T22:25:01 -27.576082 153.092415
2009-08-24T22:25:02 -27.576223 153.092530
2009-08-24T22:25:03 -27.576364 153.092648The class reads this data and distributes it via the https://() signal.
Here is the definition of the LogFilePositionSource class:
class LogFilePositionSource : public QGeoPositionInfoSource
{
Q_OBJECT
public:
LogFilePositionSource(QObject *parent = 0);
QGeoPositionInfo lastKnownPosition(bool fromSatellitePositioningMethodsOnly = false) const;
PositioningMethods supportedPositioningMethods() const;
int minimumUpdateInterval() const;
Error error() const;
public slots:
virtual void startUpdates();
virtual void stopUpdates();
virtual void requestUpdate(int timeout = 5000);
private slots:
void readNextPosition();
private:
QFile *logFile;
QTimer *timer;
QGeoPositionInfo lastPosition;
};The main methods overrided by the subclass are:
-
https://(): called by client applications to start regular position updates.
-
https://(): called by client applications to stop regular position updates.
-
https://(): called by client applications to request a single update, with a specified timeout.
When a position update is available, the subclass emits the https://() signal.
Here are the key methods in the class implementation:
LogFilePositionSource::LogFilePositionSource(QObject *parent)
: QGeoPositionInfoSource(parent),
logFile(new QFile(this)),
timer(new QTimer(this))
{
connect(timer, SIGNAL(timeout()), this, SLOT(readNextPosition()));
logFile->setFileName(":/simplelog.txt");
if (!logFile->open(QIODevice::ReadOnly))
qWarning() << "Error: cannot open source file" << logFile->fileName();
}
void LogFilePositionSource::startUpdates()
{
int interval = updateInterval();
if (interval < minimumUpdateInterval())
interval = minimumUpdateInterval();
timer->start(interval);
}
void LogFilePositionSource::stopUpdates()
{
timer->stop();
}
void LogFilePositionSource::requestUpdate(int /*timeout*/)
{
// For simplicity, ignore timeout - assume that if data is not available
// now, no data will be added to the file later
if (logFile->canReadLine())
readNextPosition();
else
emit updateTimeout();
}
void LogFilePositionSource::readNextPosition()
{
QByteArray line = logFile->readLine().trimmed();
if (!line.isEmpty()) {
QList<QByteArray> data = line.split(' ');
double latitude;
double longitude;
bool hasLatitude = false;
bool hasLongitude = false;
QDateTime timestamp = QDateTime::fromString(QString(data.value(0)), Qt::ISODate);
latitude = data.value(1).toDouble(&hasLatitude);
longitude = data.value(2).toDouble(&hasLongitude);
if (hasLatitude && hasLongitude && timestamp.isValid()) {
QGeoCoordinate coordinate(latitude, longitude);
QGeoPositionInfo info(coordinate, timestamp);
if (info.isValid()) {
lastPosition = info;
emit positionUpdated(info);
}
}
}
}List of Files▲
Files:
List of Files▲
-
logfilepositionsource/clientapplication.cpp
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logfilepositionsource/clientapplication.h
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logfilepositionsource/logfile.qrc
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logfilepositionsource/logfilepositionsource.cpp
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logfilepositionsource/logfilepositionsource.h
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logfilepositionsource/logfilepositionsource.pro
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logfilepositionsource/main.cpp