This was previously published on the Forum and gives a bit of background to how a Timetable and the Sim intract. It's really of accademic interest rather than of practical use to a timetable writer. Users of a timetable don't really need to know how it works if the timetable if it is correctly written
Loctions within the sim are of two types, Key and non-Key locations.
Generally non-Key locations will be locations on plain line where nothing happens - e.g. Exeter St Thomas. In most Sims only a handfull of timetable locations will be non-key but it will vary. While it is possible to have some activity at a non-key location (e.g. next working) it is not recommended; is not guarenteed to work and you will get an analyser warning.
Until recently you needed to have at least 2 key locations in any timetable, it is now possible to have only one: that can be used primarily to make complex splits and joins easier.
Key Locations (and entry points) are then linked in pairs to represent valid paths and when writing a timetable; it will only validate if there is a programmed path between adjacent key locations in the timetable.
Take Kings Cross for example.
Assume Kings Cross, Biggelswade and Royston are the only key locations. A path can be written between Kings Cross and Biggleswade and Kings Cross and Royston (and vv). There will be no path Royston to Biggelswade so no timetable will validate for such an attempt. However, all other non-key locations can go into the timetable anywhere regardless of whether in the line of route or not.
If you than add Hitchin to the Key Locations and then add paths to/from there to Kings Cross, Biggleswade and Royston you can now timetable a train from Royston to Biggleswade via Hitchin. If you remove the original paths then Hitchin becomes mandatory for all timetable as there is no longer a direct path Kings Cross to Biggleswade or Royston. As it is now a Key locaton Hitchin can't be in any timetable where there is not a valid path to or from it. You then need to make all the sidings/reversing points in the Hitchin area Key locations with paths to Hitchin.
That in a nutshell is the principle of key locations and how they work. Before anyone asks- the Path file, as you can maybe imagine, is a huge document with a matrix of all possible valid paths so reproducing it on the WIKI for any Sim would take up loads of space and in any event it's probably not that easy for a casual reader to understand- it's not written for that purpose.
Just to add a bit on paths (not to be confused with paths/lines in the timetable).
A Path consists of a start and an end Key location and direction of travel start and at end (that's how the train knows whether to reverse or not). With an ARS Sim rather than a single path between Key location A and Key location B you have one for every possible route between A and B all with the line/path/platform information as required so the train knows which route to take.
For example in Edinburgh to get from Edinburgh Waverley to Carlton reversing point there are 26 paths and a similar number back again.
Example of a path (one of 6 that gets you from Innerwick to Grantshouse on Edinburgh).
PIWGH4 STL=INNERWK;ENL=GTHS;SLD=U;ELD=U;SLP=ML;SLL=DL;ELP=ML;BRD=BG464,REG464BM,BG463,REG476,BG461,REG474,BG457,REG470,BG455,REG460,BG453,REG450,BG451,REG446,BG442,REG442BM,BG436.
Last edited by GeoffM on 15/09/2016 at 03:01