jokull/README.md

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# Jokullbase
How to track how late buses are:
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- [x] Download bus route data
- [x] Insert raw bus positions into timescaledb/postGIS table?
- [x] "Fan-out" JSON responses into one DB row per datapoint.
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- [ ] 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.
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- 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.
- 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.
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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.
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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;
```