52 lines
2.5 KiB
Markdown
52 lines
2.5 KiB
Markdown
# Jokullbase
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How to track how late buses are:
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- [x] Download bus route data
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- [x] Insert raw bus positions into timescaledb/postGIS table?
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- [x] "Fan-out" JSON responses into one DB row per datapoint.
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- [ ] Download routes/stops.
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- There is an endpoint called Stops.
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- There is an endpoint called Timetable, which takes a route number
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(along with day of week etc).
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- The timetable response includes a list of stops in the route,
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along with the route ID.
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- There is an endpoint called **BusLocationByStop**, which takes a
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stop ID as a parameter.
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- This information has upcoming arrivals, included estimated
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arrival time, along with the current position of the bus.
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- 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
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for bus positions.
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- [ ] Analyze actual arrival vs what the stop endpoint said about the
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arrival.
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- Use PostGIS to compute "bus arrived" event: When bus is within X
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meters of a stop on its route, mark that as an arrival event.
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- Once we have bus arrival events, we can compare them to arrivals
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throughout the day.
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- We can then discard the raw bus position data, as it's not needed
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to store it: delete every raw data point between the last arrival
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and the newly computed one.
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Arrival computation:
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- Can use edge functions for this?
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- Function takes a bus route number, start time, end time.
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- Cron in DB calls the edge functions, using state as function inputs.
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- state = last interval end time, so we can properly calculate time interval to check.
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- or rather use last ID in the raw table, so we don't skip entries.
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- Query DB to get raw bus positions in the interval.
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- Query DB to get all stops on the route (during the interval? some stops not in use sometimes)
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- For each bus ID, find the raw position where its lat,lon are X meters away from stop lat,lons.
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- These are arrival times for this bus ID, at each stop.
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- Insert into arrivals.
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- After all arrivals computed, drop all raw positions for this bus from DB.
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Useful stuff:
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```
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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
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FROM bus_stops s
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JOIN raw_bus_positions h ON ST_DWithin(s.coords, h.coords, 30)) AS buses_at_stops
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WHERE buses_at_stops.bus_id like '1%'
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ORDER BY buses_at_stops.measured_at desc;
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```
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