jokull/README.md

Jokullbase

How to track how late buses are:

• Download bus route data
• Insert raw bus positions into timescaledb/postGIS table?
  • "Fan-out" JSON responses into one DB row per datapoint.
• Download routes/stops.
  • There is an endpoint called Stops.
  • There is an endpoint called Timetable, which takes a route number (along with day of week etc).
  • The timetable response includes a list of stops in the route, along with the route ID.
  • There is an endpoint called BusLocationByStop, which takes a stop ID as a parameter.
    • This information has upcoming arrivals, included estimated arrival time, along with the current position of the bus.
  • Record stop info every few minutes, notably the arrivals.
  • This will be annoying to do only in DB since we have a trigger for bus positions.
• Analyze actual arrival vs what the stop endpoint said about the arrival.
  • Use PostGIS to compute "bus arrived" event: When bus is within X meters of a stop on its route, mark that as an arrival event.
  • Sanity check potential arrivals by removing values that are weird:
    • Bus does not belong to the route on the stop.
    • Bus not lingering at stop long enough. (e.g. driver goes right past).
    • ???
  • Once we have bus arrival events, we can compare them to arrivals throughout the day.
  • We can then discard the raw bus position data, as it's not needed to store it: delete every raw data point between the last arrival and the newly computed one.

Downloading route data:

• Fuck using GraphQL!
• https://straeto.is/en/about-straeto/open-data
• https://straeto.is/en/about-straeto/open-data/real-time-data
• https://github.com/public-transport/gtfs-via-postgres

Arrival computation:

• Can use edge functions for this?
• Function takes a bus route number, start time, end time.
• Cron in DB calls the edge functions, using state as function inputs.
  • state = last interval end time, so we can properly calculate time interval to check.
  • or rather use last ID in the raw table, so we don't skip entries.
• Query DB to get raw bus positions in the interval.
• Query DB to get all stops on the route (during the interval? some stops not in use sometimes)
• For each bus ID, find the raw position where its lat,lon are X meters away from stop lat,lons.
• These are arrival times for this bus ID, at each stop.
• Insert into arrivals.
• After all arrivals computed, drop all raw positions for this bus from DB.

Useful stuff:

SELECT buses_at_stops.* FROM (SELECT DISTINCT ON (s.id, h.measured_at) s.id, s.stop_name, ST_AsText(s.coords) as stop_coords, h.measured_at, h.bus_id, ST_AsText(h.coords) as bus_coords, ST_Distance(s.coords, h.coords) as distance
  FROM bus_stops s
    JOIN raw_bus_positions h ON ST_DWithin(s.coords, h.coords, 30)) AS buses_at_stops
    WHERE buses_at_stops.bus_id like '1%'
    ORDER BY buses_at_stops.measured_at desc;