IS:trackBegin

trackBegin
 

Schema description / Schemenbeschreibung

Position of trackBegin in the XML-Tree / Position von trackBegin im XML-Baum

• Parent: <trackTopology>
• Children: (introduced with version 2.2) <geoCoord>, <bufferStop>, <connection>, <openEnd>, <macroscopicNode>

Multiplicity / Anzahl

[1..1]

Semantics / Bedeutung

The trackBegin defines the start of a track in the railML^® file. It could be seen as a "vertex" in a "graph" where the track is an "edge".
 
Please, be aware of the semantic constraint(s)!

Attributes of trackBegin / Attribute von trackBegin

• id: XML-file-wide unique, machine-interpretable identity, required for later referencing that element internally. For a detailed explanation see Dev:identities.
  XML-Datei-weit eindeutige, maschineninterpretierbare Identität, die für die spätere interne Referenzierung dieses Elements erforderlich ist. Für eine detaillierte Erklärung siehe Dev:identities.

• pos: This is the position on a track defined as distance from its start (trackBegin) regardless the "absolute mileage" in @absPos.
  Das ist die Position des Elements auf einem Track i.S. der realen Entfernung zum trackBegin. Sie ist damit unabhängig von der mit absPos modellierten Strecken-Kilometrierung.

🗒️ For an explanation of the differences between @pos and @absPos see <mileageChange>

• absPos: This is the position on a track as absolute mileage/chainage.
  Please, be aware of semantic constraint IS:003!
  Das ist die Position des Elements im Referenzsystem der Strecken-Kilometrierung.

🗒️ For an explanation of the differences between @pos and @absPos see <mileageChange>

• absPosOffset (deprecated with version 2.1): The semantics of this attribute aren't very clear. It seems to be redundant to the definitions with mileageChanges in "overlapping regions".
• absDir (introduced with version 2.2): Defines whether the mileage increases (raising) or decreases (falling) along the <track> from this trackBegin.

🗒️ The value "raising" is a misspelling of "rising". For downward compatibility reasons, this cannot be changed.

Syntactic Constraints / Syntaktische Beschränkungen

• id: xs:ID, required
  a string, starting with a letter (a..zA..Z) or an underscore (_),
  followed by a non-colonized and non-spaced string consisting of letters, digits, points (.), dashes (-) or underscores (_)

• pos: tLengthM (xs:decimal, 6 fraction digits, length value measured in meter); required; must be greater than or equal to zero, less than or equal to the track's length
  The start of the track is described by a pos value of zero.
• absPos: tLengthM (xs:decimal, 6 fraction digits, length value measured in meter); optional
  
• absPosOffset: xs:decimal, 6 fraction digits, length value measured in meter; optional

• absDir: xs:string, generic type for mileage direction statements; enumeration raising [Sic!], falling

Semantic Constraints / Semantische Beschränkungen

Proposed Semantic Constraint "IS:003":   The value of @pos in <trackBegin> is always the lowest value of all specified <trackElements> and <ocsElements>. It is always lower than the value of @pos of <trackEnd>. The value of @pos in <trackEnd> is always the highest value of all specified <trackElements> and <ocsElements>. It is always higher than the value of @pos of <trackBegin>. Subtracting the value of @pos in <trackBegin> from the value of @pos in <trackEnd> will result in the length of the enclosing <track>. If two <track>s are connected, the @absPos values of the connected <trackBegin> and <trackEnd> must be identical if both are provided and no <mileageChange> is defined at this point and both <track>s belong to the same mileage system.   Proposed on June 17th 2019 FIXME: add Link to discussion! Please, recognize our guidelines on semantic constraints

Best practice & Examples / Empfohlene Anwendung & Beispiele

Consider the railML^® 2.3 example of Middle Rhine Railway by GPSinfradat.

TrackID	LineID	BeginElementType	EndElementType	OCP Start	OCP End
26301	2630	oE	mN	KKO	FBGK
35102	3510	oE	mN	FMZ	FBGK
35113	3511	mN	oE	FBGK	SBKNG

This code example defines a track begin that is an open end.

<trackBegin id="tB26301" pos="0" absPos="91050">
  <openEnd id="oEb26301"/>
</trackBegin>

This code example defines a track begin that is a macroscopic node.

<trackBegin id="tB35113" pos="0" absPos="-110">
  <macroscopicNode ocpRef="ocpFBGK"/>
</trackBegin>

Consider the railML^® 2.2 example of East Saxony railway network by FBS.

File:Mip3.pdf

This code example defines track begin that is a macroscopic node.

<trackBegin id='trn_DN_80.6212_1' pos='0' absPos='102100'>
  <macroscopicNode ocpRef='ocp_DN'/>
</trackBegin>

Notes / Anmerkungen

General information on positioning

Positive pos values describe the distance from the track's begin. The track length is derived from the pos value in <trackEnd>.

The absolute mileage refered to by absPos is usually found on technical drawings of the track layout or on mileage posts next to the track.

Open issues / Offene Punkte/Pendenzen

Not yet described. / Noch nicht beschrieben.