IS:trackBegin

trackBegin
 

Schema description / Schemabeschreibung

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

• 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.

Best practice & Examples / Empfohlene Anwendung & Beispiele

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

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

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

This code example defines 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.