Positioning (C++)

Positioning

The Positioning component of the Qt Location API is about the geographical position, size and address of some place. Positioning contains a QGeoCoordinate class, containing latitude, longitude and altitude in meters. QGeoLocation contains a QGeoCoordinate plus address and size information (a bounding box) so that positions can be more than mathematical points. Movement into or out of the defined bounding box areas can be monitored. The API also allows the developer to control the source of the positional information as well.

Location data involves a precisely specified position on the Earth's surface — as provided by a latitude-longitude coordinate — along with associated data, such as:

• The date and time at which the position was reported
• The velocity of the device that reported the position
• The altitude of the reported position (height above sea level)
• The bearing of the device in degrees, relative to true north

This data can be extracted through a variety of methods. One of the most well known methods of positioning is GPS (Global Positioning System), a publicly available system that uses radiowave signals received from Earth-orbiting satellites to calculate the precise position and time of the receiver. Another popular method is 'Cell Identifier Positioning', which uses the cell identifier of the cell site that is currently serving the receiving device to calculate its approximate location. These and other positioning methods can all be used with the Location API; the only requirement for a location data source within the API is that it provides a latitude-longitude coordinate with a date/time value, with the option of providing the other attributes listed above.

Location data sources are created by subclassing QGeoPositionInfoSource and providing QGeoPositionInfo objects through the QGeoPositionInfoSource::positionUpdated() signal. Clients that require location data can connect to the positionUpdated() signal and call startUpdates() or requestUpdate() to trigger the distribution of location data. The location data distribution can be stopped by calling the stopUpdates() function.

A default position source may be available on some platforms. Call QGeoPositionInfoSource::createDefaultSource() to create an instance of the default position source; the method returns 0 if no default source is available for the platform.

If a problem occurs with access to the information source then an error() signal is emitted.

The QGeoAreaMonitor class enables client applications to be notified when the receiving device has moved in or out of a particular area, as specified by a coordinate and radius. If the platform provides built-in support for area monitoring, QGeoAreaMonitor::createDefaultMonitor() returns an instance of the default area monitor.

Satellite information can also be distributed through the QGeoSatelliteInfoSource class. Call QGeoSatelliteInfoSource::createDefaultSource() to create an instance of the default satellite data source for the platform, if one is available. Alternatively, clients can subclass it to provide a custom satellite data source.

 class MyClass : public QObject
 {
     Q_OBJECT
 public:
     MyClass(QObject *parent = 0)
         : QObject(parent)
     {
         QGeoPositionInfoSource *source = QGeoPositionInfoSource::createDefaultSource(this);
         if (source) {
             connect(source, SIGNAL(positionUpdated(QGeoPositionInfo)),
                     this, SLOT(positionUpdated(QGeoPositionInfo)));
             source->startUpdates();
         }
     }

 private slots:
     void positionUpdated(const QGeoPositionInfo &info)
     {
         qDebug() << "Position updated:" << info;
     }
 };