#+TITLE: Glossary of Terms

This is meant to give a rough overview of (train-related) terms used in this
code; both for others as a reference and for me so I can remember to use them
in a (somewhat) consistent way, since they are somewhat arbitrary. I've tried
to remain at least broadly close to the terminology used by GTFS.

* Terms
** (Calendar-)Date / Day
A single, unique day (e.g. 1970-01-01). Usually used to indicate if a /trip/
is running on that day or not.

** Time (of Day)
Time on a given day, given in seconds (though often displayed as minutes)
since midnight. If a trip crosses midnight it is treated as if it took place
entirely on the previous day, and times simply count up beyond the total
number of seconds in a day (note that that's a timezone-series dependent
number).

** Trip (don't confuse with Train)
Used as in GTFS: a trip is a defined sequence of /stops/, referred to by a
number (called its trip ID, e.g. IC 94). Usually runs on multiple days.
Always has an associated /shape/.

(might match your intuition for "train line")

** Stop
A /station/ with associated arrival/departure /time/.

** Station
A train station. Tracktrain refers to each by an ID, and hopefully knows
its geolocation.

** Shape
A sequence of geolocations describing a line between stations, describing
the physical railway along which trains travel.

** Train (don't confuse with Trip)
A single instance of a /trip/ on a concrete /date/. Tracktrain mostly concerns
itself with keeping track of those; the rest is just additional stuff.

** Vehicle
An actual, physical vehicle, which might act as the /train/ going along a
/trip/ on a certain /date/.

For now tracktrain doesn't really care about them (but if it's curious it
might yet learn about them!)

** Announcement
The thing that GTFS calls "Service Alert" — a text message giving
human-readable information about some /train/.

** (Train-)Ping
A single packet of data sent from a train's /OBU/. Might arrive in some
arbitrary order.

** Control Room
The "admin interface" of tracktrain, which is not meant to be used by on-board
staff.

** On-Board Unit (OBU)
A thing on a vehicle which does geolocation tracking and yells at tracktrain
about it.

If we ever run into potential confusion regarding this term we're probably
way too professional to actually use tracktrain for anything.