capmetricsd

capmetricsd

A tool to archive GTFS-realtime data. For the time being, capmetricsd only archives Vehicle Positions from a GTFS-realtime feed.

Install

1. Install Go.
2. go get github.com/scascketta/capmetricsd
3. go install github.com/scascketta/capmetricsd

NOTE: Make sure the directory for binaries in your Go workspace (located at $GOPATH) has been added to your PATH like so:

export PATH=$PATH:$GOPATH/bin

Usage

Archiving Data

To start archiving data run:

capmetricsd start -t target-url --db db-path [--cronitor cronitor-url]

--target-url, -t 		URL to a GTFS-realtime Vehicle Positions feed
--db-path, --db 		Path to a BoltDB database (which will be created if it doesn't already exist).
--cronitor-url, --cron 	(OPTIONAL) URL to send requests to notify Cronitor (or comparable monitoring service).

This runs forever in the foreground. I recommend using some kind of process supervision service like Systemd, runit, or Supervisor to keep it running.

NOTE: capmetricsd uses an embedded key/value store called BoltDB, which stores data as a single file on disk. A process using a BoltDB database obtains a file lock when it opens the file, so be aware that you must designate a different database for each process running capmetricsd.

Retrieving Archived Data

You can access archived data as CSV data, specified with a time range in UNIX time.

capmetricsd get db dest min max

For example, to get archived data stored in a file called capmetro.boltdb from 1449813600 to 1449900000 and store the output in a file called 2015-12-11.csv:

capmetricsd get capmetro.boltdb 2015-12-11.csv 1449813600 1449900000

Internals

BUCKET (vehicle_locations)
    - BUCKET (trip_id_0)
        - timestamp_0 -> <data>
        - timestamp_1 -> <data>
        ...
        - timestamp_N -> <data>
    ...
    - BUCKET(trip_id_N)

Vehicle position data is stored in nested buckets in a BoltDB database under the bucket vehicle_locations. The vehicle_locations bucket contains buckets named by GTFS trip IDs. Each trip bucket contains all the vehicle position data for that trip, with the UNIX time for that position as the key. Keys in BoltDB are stored in byte-sorted order, so the vehicle position data in a trip bucket is sorted by time.

Public Archived Data

The captured vehicle location data for Austin's transit agency (Capital Metro) is made available the next day on the CapMetrics repo.