- Qt 6.9
- Lightning Viewer
- Qt 6.9.3 Reference Documentation

# Lightning Viewer

An application with a responsive UI showing lightning strikes on a map in real-time by combining Qt Quick, Qt Location, Qt Positioning and Qt Websockets.

Lightning Viewer is an application that receives simulated lightning strike data from a WebSocket and displays it on a map in real-time. It features a responsive UI that adapts well to mobile, tablet and desktop-sized screens in both landscape and portrait orientation. Lightning strikes appear as icons on the map, and a separate overlay shows the distance and time of the last strike. These data layers can be hidden and revealed with toggles that are accessed by pressing the map layers button. There is also a switch for switching between map types and a button that centers the map at the user's location.

#### Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, see Qt Creator: Tutorial: Build and run.

#### Application structure and relevant classes

This application follows the Model-View-Controller (MVC) pattern. The `LightningItemModel` class serves as the model. It stores a list of `LightningItemData` objects and provides methods to insert new data and to get information about the latest strikes. The View is defined in multiple QML components that display the data and user interface and handle user interaction. The `Controller` class manages the data flow between the `LightningItemModel` and the QML components. The `LightningProvider` class opens a WebSocket connection to an online server from which it receives a JSON message for each simulated lightning strike. It parses the messages and passes the data on to the `LightningItemModel` via a signal connected to a slot in the `Controller`:

     connect(m_provider.get(), &LightningProvider::dataReady, this, &Controller::onDataReceived);

Each lightning strike is represented by a `LightningItemData` struct. It contains the timestamp, latitude and longitude of the strike, and includes methods returning its distance and direction from the user location provided as a QGeoCoordinate. The `LastStrikeInfo` struct holds information about the last lightning strike.

`LightningView.qml` serves as the main view of the application. It is responsible for displaying the map and lightning data through the component `MapView.qml`, and the user controls through the component `ActionsLayer.qml`.

`MapView.qml` handles map zooming and panning. It uses a PositionSource to obtain the user’s current location and a Map to display the map. Furthermore, it includes a `LightningMapLayer.qml` for displaying the lightning data and a `DistanceTimeLayer.qml` for showing information about the last lightning strike.

`ActionsLayer.qml` provides a button for recentering the map and a custom switch control, `SwitchMap.qml`, for switching between different map types. It also includes a map layers button that reveals the map layer toggles. These toggles are defined in `MapLayersItem.qml`. In landscape orientation they appear next to the map layers button, while in horizontal orientation they are placed in a Drawer defined in `MapLayersDrawer.qml`.

#### Lightning strike data source

The application receives simulated lightning strike data from a server maintained by Qt. The server provides a WebSocket API accepting connections on the following URL:

     wss://ewea0y4bn0.execute-api.eu-north-1.amazonaws.com/production/

After connecting to the server, the application triggers the live data feed by sending the following JSON message to the server:

     "{\"action\": \"simulatelightningdata\"}"

#### Source files

Example project @ code.qt.io

See also All Qt Examples, Qt Quick Examples and Tutorials, Qt Location Examples, Qt Positioning Examples, and Qt WebSockets Examples.