Inconsistency in trip update example vs. reference documentation?

[niels-penneman]

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The trip update examples maintained at https://github.com/google/transit/blob/master/gtfs-realtime/spec/en/examples/trip-updates-full.asciipb and shown at https://gtfs.org/realtime/feed-examples/trip-updates/ contain StopTimeUpdate messages with just a stop sequence number in the second and third entities.

Extract taken from the second entity:

stop_time_update {
  # selected by stop_sequence. It will update the vehicle's arrival time
  stop_sequence: 10
  # with the default delay of 0 (on time) and propagate this update
  # for the rest of the vehicle's stops.
}

The reference documentation for a StopTimeUpdate message however states that the arrival and departure fields are conditionally required, with the following clause:

If schedule_relationship is empty or SCHEDULED, either arrival or departure must be provided within a StopTimeUpdate - both fields cannot be empty. arrival and departure may both be empty when schedule_relationship is SKIPPED. If schedule_relationship is NO_DATA, arrival and departure must be empty.

This suggests the example should specify at least one of the fields, or explicitly set schedule_relationship to NO_DATA. In my understanding, using NO_DATA will effectively reset the delays to zero and stop propagation of any previously specified delay. NO_DATA is however defined as "no realtime timing information available"—which may not be semantically correct when we know the actual delay to be zero.

What are your thoughts?

[eliasmbd]

@niels-penneman Thank you for bringing this up here in you first issue on the google/transit repo. We appreciate your contribution to GTFS! 🎉

I am sure the community will get back to you in no time.