era-dual-positioning

name	era-dual-positioning
description	Implement the ERA dual positioning model — TopologicalCoordinate (micro-topology offset) plus LinearPositioningSystemCoordinate (KilometricPost + offset) — for infrastructure elements. Use when writing or debugging any SPARQL CONSTRUCT query that positions an element on the network, or when understanding why an element is missing LRS or topology coordinates.

ERA Dual Positioning Model

The model supports two complementary positioning references:

Reference type	Purpose	Based on
era:TopologicalCoordinate	Micro-topology position	era:LinearElement + era:offsetFromOrigin
era:LinearPositioningSystemCoordinate	Linear referencing position	era:KilometricPost + era:offsetFromKilometricPost

Both hang off an era:NetPointReference (for point elements) or are attached to the era:startsAt / era:endsAt NetPointReference nodes of a era:NetLinearReference (for linear elements).

Complete Object Graph

InfrastructureElement
  └─ era:netReference ──▶ NetPointReference         (or startsAt/endsAt of NetLinearReference)
        ├─ era:hasTopoCoordinate ──▶ TopologicalCoordinate
        │       ├─ era:onLinearElement ──▶ LinearElement   (micro-level)
        │       └─ era:offsetFromOrigin ──▶ xsd:double     (metres from element origin)
        └─ era:hasLrsCoordinate ──▶ LinearPositioningSystemCoordinate
                ├─ era:kmPost ──▶ KilometricPost            (shared)
                │       ├─ era:hasLRS ──▶ LinearPositioningSystem
                │       └─ era:kilometer ──▶ xsd:double     (rounded km number)
                └─ era:offsetFromKilometricPost ──▶ xsd:double  (metres within that km)

SPARQL CONSTRUCT Template (point element)

PREFIX era: <http://data.europa.eu/949/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX xyz: <http://sparql.xyz/facade-x/data/>
PREFIX fx:  <http://sparql.xyz/facade-x/ns/>

CONSTRUCT {
  # --- topological coordinate ---
  ?eraElement era:netReference ?netPointRef .

  ?netPointRef a era:NetPointReference ;
               era:appliesToDirection ?orientation ;
               era:hasTopoCoordinate ?topoCoord .

  ?topoCoord a era:TopologicalCoordinate ;
             era:onLinearElement ?linearElement ;
             era:offsetFromOrigin ?posDouble .

  # --- LRS coordinate (OPTIONAL block; only emitted when linearCoordinate present) ---
  ?netPointRef era:hasLrsCoordinate ?lrsCoord .

  ?lrsCoord a era:LinearPositioningSystemCoordinate ;
            era:kmPost ?kmPost ;
            era:offsetFromKilometricPost ?kmOffset .

  ?kmPost a era:KilometricPost ;
          era:hasLRS ?eraLPS ;
          era:kilometer ?kmNumber .
}
WHERE {
  ...
}

SPARQL CONSTRUCT Template (linear element — startsAt / endsAt)

For RunningTrack, Siding, PlatformEdge etc., each NetLinearReference has a startsAt and endsAt NetPointReference. Apply the dual coordinate pattern to both:

CONSTRUCT {
  ?netLinRef a era:NetLinearReference ;
             era:hasSequence ?sequenceHead ;
             era:startsAt ?startRef ;
             era:endsAt   ?endRef .

  # Start NetPointReference + coordinates
  ?startRef a era:NetPointReference ;
            era:hasTopoCoordinate ?startTopoCoord ;
            era:hasLrsCoordinate  ?startLrsCoord .       # OPTIONAL

  ?startTopoCoord a era:TopologicalCoordinate ;
                  era:onLinearElement ?firstLinearElement ;
                  era:offsetFromOrigin ?startOffset .

  # (lrsCoord triples for start …)

  # End NetPointReference + coordinates
  ?endRef a era:NetPointReference ;
          era:hasTopoCoordinate ?endTopoCoord ;
          era:hasLrsCoordinate  ?endLrsCoord .           # OPTIONAL

  ?endTopoCoord a era:TopologicalCoordinate ;
                era:onLinearElement ?lastLinearElement ;
                era:offsetFromOrigin ?endOffset .

  # (lrsCoord triples for end …)
  ...
}

KilometricPost Sharing

KilometricPost URIs could be minted from {posSystemRef}_km_{roundedKm} — the same URI is emitted by every element at that kilometer on the same system. SPARQL CONSTRUCT will naturally merge duplicate triples, so no deduplication is needed.