Qt Positioning NMEA plugin

概述

Included with Qt Positioning is a position plugin which parses NMEA sentences into position updates. This plugin can use serial port, socket or file as a source.

This plugin can be loaded by using the provider name nmea .

参数

The following table lists parameters that can be passed to the nmea plugin.

参数	描述
nmea.source	The source that will be used to get NMEA data.
nmea.satellite_info_simulation_interval	The interval for reading satellite information data from the file in simulation mode.

Different sources require different ways of providing the data. The following table lists different ways of providing nmea.source parameter for socket, serial port and file inputs.

Scheme	范例	描述
socket://hostname:port	`socket://localhost:12345`	使用 socket: keyword to specify that you want to get the nmea data from the socket. A TCP socket will be created, which will try to connect to host `hostname` using port `port` . Upon successful connection a text NMEA stream is expected to be received from the server.
serial:portname	`serial:/dev/ttyUSB0`	使用 serial: keyword to specify that you want to get the nmea data from the serial port. The plugin will try to establish a connection to port `portname` with baudrate = 4800 Bd. Upon successful connection a text NMEA stream is expected to be received from the serial port. If you use serial: without any port name, the plugin will try to find one of the well known serial devices using vendor identifier. Note however that this is not a recommended way of using the serial port connection, as the list of well-known devices is small and most probably does not include your hardware.
	`serial:COM1`
	`serial:`
filepath	`/home/user/nmealog.txt`	使用 file:/// or just full file path to specify a path to a local file.
file:///filepath	`file:///home/user/nmealog.txt`
qrc:///filepath	`qrc:///nmealog.txt`	使用 qrc:/// prefix to specify a path to a file in the application resources.

注意： 若 nmea.source parameter is not specified, the plugin will try to locate one of the well-known serial devices (as if nmea.source = serial: was specified).

Position source usage example

The following examples show how to create a nmea PositionSource using different data sources.

QML

// text file
PositionSource {
    name: "nmea"
    PluginParameter { name: "nmea.source"; value: "qrc:///nmealog.txt" }
}
// socket
PositionSource {
    name: "nmea"
    PluginParameter { name: "nmea.source"; value: "socket://localhost:22222" }
}
// serial port
PositionSource {
    name: "nmea"
    PluginParameter { name: "nmea.source"; value: "serial:/dev/ttyACM0" }
}

C++

// text file
QVariantMap params;
params["nmea.source"] = "qrc:///nmealog.txt";
QGeoPositionInfoSource *textPositionSource = QGeoPositionInfoSource::createSource("nmea", params, this);
// socket
params["nmea.source"] = "socket://localhost:22222";
QGeoPositionInfoSource *socketPositionSource = QGeoPositionInfoSource::createSource("nmea", params, this);
// serial port
params["nmea.source"] = "serial:/dev/ttyACM0";
QGeoPositionInfoSource *serialPositionSource = QGeoPositionInfoSource::createSource("nmea", params, this);

注意： 一旦 PositionSource is created, it can't be reconfigured to use other type of source data.

Satellite information source usage example

Apart from the position information, nmea plugin is also capable of providing satellite information. For now it does not have any QML object, but can be created directly from C++ code.

// serial port
QVariantMap parameters;
parameters["nmea.source"] = "serial:/dev/ttyUSB0";
QGeoSatelliteInfoSource *serialSource = QGeoSatelliteInfoSource::createSource("nmea", parameters, this);
// socket
parameters["nmea.source"] = "socket://localhost:22222";
QGeoSatelliteInfoSource *socketSource = QGeoSatelliteInfoSource::createSource("nmea", parameters, this);

If you want to use QGeoSatelliteInfoSource to read file with NMEA stream, you can also use additional parameter "nmea.satellite_info_simulation_interval" . This parameter is used to specify the playback rate (in milliseconds) for the satellite info messages. The minimum allowed frequency is specified by minimumUpdateInterval() . If you specify a smaller value, it will be ignored. If no value is specified, the default value is qMax(100, minimumUpdateInterval()) . At runtime QNmeaSatelliteInfoSource::setBackendProperty () method can be used to update this parameter.

// file
QVariantMap parameters;
parameters["nmea.source"] = "qrc:///nmealog.txt";
parameters["nmea.satellite_info_simulation_interval"] = 1000;
QGeoSatelliteInfoSource *fileSource = QGeoSatelliteInfoSource::createSource("nmea", parameters, this);

This parameter is not applicable to position source because NMEA protocol already has timestamps in position messages. These timestamps are used to simulate the correct message rate while using QGeoPositionInfoSource with file as a data source.

注意： 一旦 QGeoSatelliteInfoSource is created, it can't be reconfigured to use other type of source data.