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    hafas-monitor-trips

    6.3.0 • Public • Published

    hafas-monitor-trips

    Using a HAFAS endpoint, watch all movements/vehicles in a bounding box, and optionally their trips.

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    hafas-monitor-trips will periodically fetch all movements/vehicles in the whole bounding box. If configured, it will then fetch each vehicle's whole trip to get up-to-date data about its stopovers.

    Installation

    Note: hafas-monitor-trips needs access to Redis. Set the REDIS_URL environment variable to configure access to it.

    npm install hafas-monitor-trips

    Usage

    In the following example, we'll keep things simple:

    • We use vbb-hafas, a HAFAS client querying endpoint of the Berlin & Brandenburg public transport service (VBB).
    • We monitor a small bounding box in the center of Berlin.
    • We console.log all positionss (of all movements/vehicles being monitored).

    Note: hafas-monitor-trips only works with hafas-client@5-compatible API clients.

    const createHafas = require('vbb-hafas')
    const createMonitor = require('hafas-monitor-trips')
    
    const bbox = { // Potsdamer Platz in Berlin
    	north: 52.52,
    	west: 13.36,
    	south: 52.5,
    	east: 13.39,
    }
    
    const hafas = createHafas('hafas-monitor-trips example')
    const monitor = createMonitor(hafas, bbox)
    
    monitor.on('error', err => console.error(err))
    monitor.on('hafas-error', err => console.error(err))
    monitor.on('hafas-client-error', err => console.error(err))
    monitor.on('position', (loc, movement) => console.log(loc, movement))

    You can listen for these events:

    • error – An error occured, e.g. a network error.
    • hafas-error – The HAFAS endpoint rejected a request with an error.
    • hafas-client-errorhafas-client failed to process the HAFAS response.
    • position – The current (estimated) position and full details of a movement/vehicle.

    If you listen to position events, you'll receive all movements (a movement one of >0 results of a radar() call) which are within the bounding box right now. Each movement will not have all stopovers of its trip though, just the next few; If you want to access all stopovers, you need to fetch the respective trip (see below).

    fetching trips

    You can configure hafas-monitor-trips to also fetch a movements trip, including all its stopovers. You can configure

    • which movements/vehicles to fetch the trip for (e.g. all, or just buses starting with "1"), as well as
    • when to fetch the trip (by default, right after the movement/vehicle has been fetched, see below for more details), the trip fetching strategy.

    These additional events will be emitted:

    • trip – Every trip that has been fetched.
    • stopover – Each stopover of every trip that has been fetched.

    fetching trips right away

    For example, we can fetch all buses' trips, right away:

    const fetchTrips = require('hafas-monitor-trips/fetch-trips')
    const rightAwayStrategy = require('hafas-monitor-trips/fetch-trips/right-away')
    
    const shouldFetchTrip = movement => movement.line.product === 'bus'
    fetchTrips(monitor, rightAwayStrategy(shouldFetchTrip))
    
    monitor.on('trip', trip => console.log(trip.stopovers))

    fetching important trips first

    You can control the order in which the trips get fetched. For example, let's fetch the "A" line's trips first, then all other buses' trips:

    const fetchTrips = require('hafas-monitor-trips/fetch-trips')
    const priorityBasedStrategy = require('hafas-monitor-trips/fetch-trips/priority-based')
    
    const shouldFetchTrip = (movement) => {
    	if (movement.line.product === 'bus') {
    		return movement.line.name === 'A' ? 1 : 0
    	}
    	return null // don't fetch other products
    }
    fetchTrips(monitor, priorityBasedStrategy(shouldFetchTrip))

    fetching trips with a delay

    You can fetch the trips after a certain delay. For example, let's fetch trips after 10s, but only for movements with a delayed next stopover:

    const fetchTrips = require('hafas-monitor-trips/fetch-trips')
    const timeBasedStrategy = require('hafas-monitor-trips/fetch-trips/time-based')
    
    const shouldFetchTrip = (movement) => {
    	const nextStopover = movement.nextStopovers[0]
    	if (nextStopover && nextStopover.arrivalDelay > 0) {
    		return 10 * 1000
    	}
    	return null // don't fetch other movements' trips
    }
    fetchTrips(monitor, timeBasedStrategy(shouldFetchTrip))

    preventing excessive requests

    If you fetch all movements' trips, with a bounding larger than a few km², there will be so many HAFAS calls made that you will likely get rate-limited by the HAFAS endpoint; The amount depends on the specific endpoint. This is how you can reduce the request rate:

    • Use the shouldFetchTrip(movement) function to restrict the number of movements/vehicles that you fetch trips of, e.g. to only the line you're interested in, or only buses.
    • Instead of passing a hafas-client instance directly into hafas-monitor-trips, use hafas-client/throttle to prevent bursts of requests. You will have to experiment with the rate until you get a balance, between not sending too many requests, and being able to monitor all relevant trips.
    • Use e.g. hafas-client-rpc to run the requests from a pool of worker machines.

    Contributing

    If you have a question or need support using hafas-monitor-trips, please double-check your code and setup first. If you think you have found a bug or want to propose a feature, refer to the issues page.

    Install

    npm i hafas-monitor-trips

    DownloadsWeekly Downloads

    24

    Version

    6.3.0

    License

    ISC

    Unpacked Size

    33.1 kB

    Total Files

    14

    Last publish

    Collaborators

    • derhuerst