Log File Position Source (C++) ¶

The Logfile Position Source shows how to create and work with a custom NMEA position source, for platforms without GPS.

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 153.092648
										

The class reads this data and distributes it via the positionUpdated() 信号。

Here is the definition of the LogFilePositionSource 类：

The main methods overrided by the subclass are:

• startUpdates() : called by client applications to start regular position updates.

• stopUpdates() : called by client applications to stop regular position updates.

• requestUpdate() : called by client applications to request a single update, with a specified timeout.

When a position update is available, the subclass emits the positionUpdated() 信号。

Here are the key methods in the class implementation:

范例工程 @ code.qt.io