Satellite Info

This example demonstrates the usage of Qt Positioning QML API:

• PositionSource
• SatelliteSource

The example also shows how to use a custom C++ model together with a custom proxy model from QML.

UI Overview

The example shows satellite information in three different tabs. The data is taken from the SatelliteSource::satellitesInView and SatelliteSource::satellitesInUse properties.

The Sky View tab shows the relative satellite positions using the Azimuth and Elevation attributes. Clicking on an individual satellite object opens a popup with the satellite identifier, its azimuth and elevation.

The Table View tab shows the list of all detected satellites, and allows to apply sorting and filtering to the list.

The RSSI View tab shows the signal strength of satellites in view using the signalStrength property. The numbers below the bars represent the individual satellite identifiers.

The Sky View and RSSI View tabs also show the current latitude and longitude. They use PositionSource::position property to extract this information.

The Status block on top of the tabs shows the current mode or the last error.

The Settings menu allows to switch the application color mode and show the help information.

The application operates in three different modes:

The application automatically switches into a simulation mode if the platform does not provide satellite or position information. The simulation mode uses an NMEA plugin with pre-recorded NMEA data.

Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

Retrieving Current Position

The current position is retrieved from the PositionSource QML object. The onPositionChanged handler is used to receive position updates. The string representations of latitude and longitude are extracted from the coordinate property.

 PositionSource {
     id: positionSource
     name: root.simulation ? "nmea" : ""
     onPositionChanged: {
         let posData = position.coordinate.toString().split(", ")
         positionBox.latitudeString = posData[0]
         positionBox.longitudeString = posData[1]
     }
 }

Retrieving Satellite Information

Similarly to the position, the current satellite information is retrieved from the SatelliteSource QML object. The onSatellitesInViewChanged and onSatellitesInUseChanged handlers are used to get the updated satellites in view and satellites in use respectively. In this example, the data is then forwarded to the C++ model, which is later used in all views.

 SatelliteSource {
     id: satelliteSource
     name: root.simulation ? "nmea" : ""
     onSatellitesInViewChanged: root.satellitesModel.updateSatellitesInView(satellitesInView)
     onSatellitesInUseChanged: root.satellitesModel.updateSatellitesInUse(satellitesInUse)
 }

Using Custom C++ Models

The example makes use of two custom models - SatelliteModel and SortFilterModel.

Satellite Model

The SatelliteModel class is derived from QAbstractListModel and reimplements the rowCount(), data(), and roleNames() methods to represent the satellite information. Using QAbstractListModel as a base class allows to easily use the model with the QML ListView and Repeater types. A custom size property is used only in the RSSI View tab to dynamically calculate the width of the tab bars.

 class SatelliteModel : public QAbstractListModel
 {
     Q_OBJECT
     Q_PROPERTY(int size READ rowCount NOTIFY sizeChanged)
     QML_ELEMENT
 public:
     explicit SatelliteModel(QObject *parent = nullptr);

     int rowCount(const QModelIndex &parent = QModelIndex()) const override;
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
     QHash<int, QByteArray> roleNames() const override;

 public slots:
     void updateSatellitesInView(const QList<QGeoSatelliteInfo> &inView);
     void updateSatellitesInUse(const QList<QGeoSatelliteInfo> &inUse);

 signals:
     void sizeChanged();
 };

The roleNames() method is used to map the model's roles to the property names which can be used to access the model data from QML. For example, the id name is used to extract the satellite identifier, and the rssi name is used to get the signal strength.

 QHash<int, QByteArray> SatelliteModel::roleNames() const
 {
     return {
         {Roles::IdRole, "id"},
         {Roles::RssiRole, "rssi"},
         {Roles::AzimuthRole, "azimuth"},
         {Roles::ElevationRole, "elevation"},
         {Roles::SystemRole, "system"},
         {Roles::SystemIdRole, "systemId"},
         {Roles::InUseRole, "inUse"},
         {Roles::VisibleNameRole, "name"}
     };
 }

On the QML side, we can use these names to get the actual values. For example, the implementation of RSSI View uses the rssi, inUse, and id role names to draw the bars that represent individual satellites:

 Repeater {
     id: repeater
     model: root.satellitesModel
     delegate: Rectangle {
         required property var modelData
         height: rect.height
         width: view.singleWidth
         color: "transparent"
         SemiRoundedRectangle {
             anchors.bottom: satId.top
             width: parent.width
             height: (parent.height - satId.height)
                     * Math.min(parent.modelData.rssi, rect.maxVisibleLevel)
                     / rect.maxVisibleLevel
             color: parent.modelData.inUse ? root.inUseColor : root.inViewColor
         }
         Text {
             id: satId
             anchors.horizontalCenter: parent.horizontalCenter
             anchors.bottom: parent.bottom
             text: parent.modelData.id
             color: Theme.textSecondaryColor
             font.pixelSize: Theme.smallFontSize
             font.weight: Theme.fontLightWeight
         }
     }
 }

Proxy Model

The SortFilterModel class is used to provide custom sorting and filtering of the satellite objects shown in the Table View tab.

The model is derived from QSortFilterProxyModel and reimplements the filterAcceptsRow() and lessThan() methods to provide filtering and sorting. The model also exposes several slots to tune the filtering and sorting behavior.

 class SortFilterModel : public QSortFilterProxyModel
 {
     Q_OBJECT
     QML_ELEMENT
 public:
     explicit SortFilterModel(QObject *parent = nullptr);

 public slots:
     void updateFilterString(const QString &str);
     void updateShowInView(bool show);
     void updateShowInUse(bool show);
     void updateSelectedSystems(int id, bool show);
     void updateSortRoles(int role, bool use);

 protected:
     bool filterAcceptsRow(int row, const QModelIndex &parent) const override;
     bool lessThan(const QModelIndex &left, const QModelIndex &right) const override;
 };

These slots can be called from both C++ and QML. For example, the Satellite Identifier delegate uses the updateSelectedSystems() slot to show or hide the information about satellites belonging to certain satellite systems. Likewise, the Satellite Status delegates use the updateShowInView() and updateShowInUse() slots to filter the satellites with a specific status.

 Repeater {
     model: root.satelliteSystemModel
     delegate: CheckElement {
         required property var modelData
         text: modelData.name
         Layout.alignment: Qt.AlignRight
         onCheckedChanged: {
             root.sortFilterModel.updateSelectedSystems(modelData.id, checked)
         }
     }
 }
     ...
 CheckElement {
     text: qsTr("In View")
     Layout.alignment: Qt.AlignRight
     onCheckedChanged: root.sortFilterModel.updateShowInView(checked)
 }
 CheckElement {
     text: qsTr("In Use")
     Layout.alignment: Qt.AlignRight
     onCheckedChanged: root.sortFilterModel.updateShowInUse(checked)
 }

QML Module Registration

CMake Build

For a CMake-based build, we need to add the following to the CMakeLists.txt:

 qt_add_qml_module(satelliteinfo
     URI SatelliteInformation
     VERSION 1.0
     SOURCES
         roles.h
         satellitemodel.cpp satellitemodel.h
         sortfiltermodel.cpp sortfiltermodel.h
     QML_FILES
         ApplicationScreen.qml
         Button.qml
         Header.qml
         HelpPopup.qml
         LegendBox.qml
         Main.qml
         RssiView.qml
         PageButton.qml
         PermissionsScreen.qml
         PositionBox.qml
         SatelliteView.qml
         SettingsView.qml
         SkyView.qml
         Theme.qml
         ViewSwitch.qml
     RESOURCES
         icons/checkbox.svg
         icons/checkbox_blank.svg
         icons/darkmode.svg
         icons/filter.svg
         icons/help.svg
         icons/lightmode.svg
         icons/place.svg
         icons/qtlogo_green.png
         icons/qtlogo_white.png
         icons/rssiview.svg
         icons/satellite_small.png
         icons/satellite1.png
         icons/satellite2.png
         icons/search.svg
         icons/settings.svg
         icons/skyview.svg
         icons/sort.svg
         icons/tableview.svg
 )

qmake Build

For a qmake build, we need to modify the satelliteinfo.pro file in the following way:

 CONFIG += qmltypes
 QML_IMPORT_NAME = SatelliteInformation
 QML_IMPORT_MAJOR_VERSION = 1

 qml_resources.files = \
     qmldir \
     ApplicationScreen.qml \
     Button.qml \
     Header.qml \
     HelpPopup.qml \
     LegendBox.qml \
     Main.qml \
     RssiView.qml \
     PageButton.qml \
     PermissionsScreen.qml \
     PositionBox.qml \
     SatelliteView.qml \
     SettingsView.qml \
     SkyView.qml \
     Theme.qml \
     ViewSwitch.qml

 qml_resources.prefix = /qt/qml/SatelliteInformation

 RESOURCES += qml_resources

 icon_resources.files = \
     icons/checkbox.svg \
     icons/checkbox_blank.svg \
     icons/darkmode.svg \
     icons/filter.svg \
     icons/help.svg \
     icons/lightmode.svg \
     icons/place.svg \
     icons/qtlogo_green.png \
     icons/qtlogo_white.png \
     icons/rssiview.svg \
     icons/satellite_small.png \
     icons/satellite1.png \
     icons/satellite2.png \
     icons/search.svg \
     icons/settings.svg \
     icons/skyview.svg \
     icons/sort.svg \
     icons/tableview.svg

 icon_resources.prefix = /qt/qml/SatelliteInformation

 RESOURCES += icon_resources

Example project @ code.qt.io