TD: Difference between revisions

Revision as of 11:54, 8 October 2012

Overview

What on earth is this?

The TD feed provides low-level detail about the position of trains and their train reporting number through a network of berths. Usually, but not always, a berth is associated with a signal - but there are locations (such as terminal platforms at stations) where there may be more than one berth.

From each berth, there are zero or more other berths which a train description may move, or 'step' in to. Some of these may be one-way, some may be two-way.

Message types

The Train Describer feed has four message types:

CA - Berth Step, where a description moves 'from' a berth, 'to' another berth
CB - Berth Cancel, where a description is removed from a berth
CC - Berth Interpose, where a description is interposed (placed in to) a berth
CT - Heartbeat

With the exception of the CT message type, TD messages include a four-character train description. At present, only class 1, 2 and 9 trains are included in the feed.

Format

Messages are sent in JSON format, as follows:

{"CA_MSG"=>{"time"=>"1349696911000", "area_id"=>"SK", "msg_type"=>"CA", "from"=>"3647", "to"=>"3649", "descr"=>"1F42"}}
{"CB_MSG"=>{"time"=>"1349696911000", "area_id"=>"G1", "msg_type"=>"CB", "from"=>"G669", "descr"=>"2J01"}}
{"CC_MSG"=>{"time"=>"1349696911000", "area_id"=>"G1", "msg_type"=>"CC", "descr"=>"2J01", "to"=>"G669"}}
{"CT_MSG"=>{"time"=>"1349696911000", "area_id"=>"SA", "msg_type"=>"CT", "report_time"=>"1249"}}

@@ Line 1: / Line 1: @@
 == Overview ==
-The Train Describer feed contains message about Train movements at the Signal Berth Level. Messages come in 4 types, all in JSON format:
+=== What on earth is this? ===
-* CA - Berth Step
+The TD feed provides low-level detail about the position of trains and their train reporting number through a network of berths.  Usually, but not always, a berth is associated with a signal - but there are locations (such as terminal platforms at stations) where there may be more than one berth.
-* CB - Berth Cancel
-* CC - Berth Interpost
-* CT - Heartbeat
-Messages only exist for trains of [[headcode|headcodes]] classes, 1, 2 and 9.
+From each berth, there are zero or more other berths which a train description may move, or 'step' in to.  Some of these may be one-way, some may be two-way.
-== Messages ==
+=== Message types ===
-Messages consist of a reference key and then the main JSON string.
+The Train Describer feed has four message types:
-The Reference key is the message type followed by _MSG, all in Upper case.
+* CA - Berth Step, where a description moves 'from' a berth, 'to' another berth
+* CB - Berth Cancel, where a description is removed from a berth
-Each message can contain the keys,
+* CC - Berth Interpose, where a description is interposed (placed in to) a berth
+* CT - Heartbeat
-* to
-* time, in Milliseconds
-* area_id, see [[TD_Areas]]
-* msg_type
-* from
-* descr, the Train's [[headcode]]
-* report_time, eg 0842, is 9:42 in the morning,
-=== CA ===
-Contains: to, time, area_id, msg_type, from, descr
-==== Example ====
-  {
-    "CA_MSG": {
-      "to": "0041",
-      "time": "1338289664000",
-      "area_id": "LB",
-      "msg_type": "CA",
-      "from": "0033",
-      "descr": "2T33"
-    }
-  }
-=== CB ===
-Contains: time, area_id, msg_type, from, descr
-==== Example ====
-  {
-    "CB_MSG": {
-      "time": "1338289665000",
-      "area_id": "SK",
-      "msg_type": "CB",
-      "from": "4333",
-      "descr": "1U29"
-    }
-  }
-=== CC ===
-Contains: to, time, area_id, msg_type, descr
-==== Example ====
-  {
-    "CC_MSG": {
-      "to": "FN13",
-      "time": "1338289665000",
-      "area_id": "ZG",
-      "msg_type": "CC",
-      "descr": "1A40"
-    }
-  }
-=== CT ===
+With the exception of the CT message type, TD messages include a four-character train description.  At present, only class 1, 2 and 9 trains are included in the feed.
-Contains: time, area_id, msg_type, report_time
+== Format ==
-==== Example ====
+Messages are sent in JSON format, as follows:
-  {
+* {"CA_MSG"=>{"time"=>"1349696911000", "area_id"=>"SK", "msg_type"=>"CA", "from"=>"3647", "to"=>"3649", "descr"=>"1F42"}}
-    "CT_MSG": {
+* {"CB_MSG"=>{"time"=>"1349696911000", "area_id"=>"G1", "msg_type"=>"CB", "from"=>"G669", "descr"=>"2J01"}}
-      "time": "1338289669000",
+* {"CC_MSG"=>{"time"=>"1349696911000", "area_id"=>"G1", "msg_type"=>"CC", "descr"=>"2J01", "to"=>"G669"}}
-      "area_id": "WJ",
+* {"CT_MSG"=>{"time"=>"1349696911000", "area_id"=>"SA", "msg_type"=>"CT", "report_time"=>"1249"}}
-      "msg_type": "CT",
-      "report_time": "0842"
-    }
-  }