Heavy lifting of real-time data is done in other systems. Digitransit integrates itself to various datasources in order to read real-time data from the vehicles. How this is done depends on which region we are talking about.
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|https://github.com/HSLdevcom/transitdata||Processes HSL realtime data with Apache Pulsar. Produces GTFS-RT messages from internal data formats.|
|https://github.com/HSLdevcom/siri2gtfsrt||Convert SIRI JSON to GTFS-RT trip updates|
|https://github.com/HSLdevcom/raildigitraffic2gtfsrt||Converts digitraffic train updates into GTFS-RT Trip Updates|
|https://github.com/HSLdevcom/gtfsrthttp2mqtt||Reads GTFS-RT over HTTP and publishes it as MQTT data|
|https://developers.google.com/transit/||Google transit community|
|https://groups.google.com/forum/#!forum/gtfs-realtime||Google transit forum|