Observed Stop Events from GTFS-Realtime Trip Updates

Reduces an archive of Trip Updates (many successive predictions per trip and stop across polls) to observed stop events (see observed-stop-events): per (trip, service date, stop visit), the latest report wins - labeled "observed" when it was issued at or after the vehicle's departure from the stop, "predicted-last" otherwise. SKIPPED stops and CANCELED/DELETED trips become explicit negative-information rows; NO_DATA rows are dropped with a message.

Usage

rt2s_events_from_trip_updates(updates, baseline = NULL, tz = "UTC")

Arguments

updates

A data.frame as returned by gtfsrealtime::read_gtfsrt_trip_updates(): one row per stop-time update with trip_id, stop_id and/or stop_sequence, arrival_time/arrival_delay, departure_time/departure_delay, schedule relationships, start_date, vehicle_id, file_timestamp. When trip_id is absent (some producers, e.g. HSL, identify trips only by the GTFS-RT TripDescriptor), a stable identity is synthesized from route_id, direction_id, start_date, and start_time so predictions still group per operated trip.

baseline

Optional baseline static GTFS feed (object or zip path). Required to resolve delay-only updates (a delay without an absolute time can only be interpreted against the scheduled time).

tz

Timezone of the feed's service days (used to resolve delay-only updates against baseline scheduled times). Default "UTC".

Value

A validated observed stop events data.table.

Details

A trip that serves a stop more than once (a loop) keeps one event per visit, told apart by stop_sequence as GTFS-Realtime requires for such stops. A stop counts as looped when one poll lists it under two stop_sequence values; elsewhere all reports of a stop form one visit even if a producer renumbers stops between polls. At a looped stop a report without stop_sequence is ambiguous and dropped with a warning. Delay-only updates are resolved against the baseline row with the same stop_sequence when that row is the same stop (a warning names sequences that point at another stop), else against a stop the scheduled trip serves once. A trip without start_date whose report falls in the first hour of a daylight-saving fall-back day belongs to the previous service day, as GTFS counts that hour past 24:00 of the day before.