IfcProjectedCRS

Natural language names
deProjiziertes Koordinatenreferenzsystem
enProjected CRS
Change log
ItemSPFXMLChangeDescription
IFC2x3 to IFC4
    IfcProjectedCRSADDED
IFC4 Addendum 1
    IfcProjectedCRS
      NameMODIFIEDInstantiation changed from OPTIONAL.
      GeodeticDatumMODIFIEDInstantiation changed to OPTIONAL.
      HasCoordinateOperationADDED
Semantic definitions at the entity
Entity definition

IfcProjectedCRS is a coordinate reference system of the map to which the map translation of the local engineering coordinate system of the construction or facility engineering project relates. The MapProjection and MapZone attributes uniquely identify the projection to the underlying geographic coordinate reference system, provided that they are well-known in the receiving application. The projected coordinate reference system is assumed to be a 2D or 3D right-handed Cartesian coordinate system, the optional MapUnit attribute can be used determine the length unit used by the map.

NOTE  Definition from OpenGIS Abstract Specification, Topic 2:
A 2D (or with vertical coordinate axis 3D) coordinate reference system used to approximate the shape of the earth on a planar surface, but in such a way that the distortion that is inherent to the approximation is carefully controlled and known. Distortion correction is commonly applied to calculated bearings and distances to produce values that are a close match to actual field values.

The unambiguous identifier by which the coordinate reference system is know, is stored in the inherited Name attribute. Well defined identifiers include the map projection and also the map zone information. In these cases the MapProjection and the MapZone attributes can be omitted.

EXAMPLE  The identifier 'EPSG:25832' defines the map projection 'UTM' and the zone '32N' in additon to the geodetic and vertical datum.
HISTORY  New entity in IFC4.
Attribute definitions
#AttributeTypeCardinalityDescription C
5MapProjectionIfcIdentifier[0:1] Name by which the map projection is identified.
EXAMPLE  map projects include:
  • UTM
  • Gaus-Krueger
X
6MapZoneIfcIdentifier[0:1] Name by which the map zone, relating to the MapProjection, is identified.
EXAMPLE 
  • for UTM, the zone number, like 32 for UTM32
  • for Gaus-Krueger, the zones of longitudinal width, like 3'
X
7MapUnitIfcNamedUnit[0:1] Unit of the coordinate axes composing the map coordinate system.
NOTE  Only length measures are in scope and all two or three axes of the map coordinate system shall have the same length unit.
X
Formal Propositions
RuleDescription
IsLengthUnitThe map unit shall be given, if present, as a length unit.
Inherited definitions from supertypes
Entity inheritance IfcCoordinateReferenceSystem
Attribute inheritance
#AttributeTypeCardinalityDescriptionC
IfcCoordinateReferenceSystem
1NameIfcLabel[1:1] Name by which the coordinate reference system is identified.
NOTE  The name shall be taken from the list recognized by the European Petroleum Survey Group EPSG. It should then be qualified by the EPSG name space, for example as 'EPSG:5555'.
X
2DescriptionIfcText[0:1] Informal description of this coordinate reference system. X
3GeodeticDatumIfcIdentifier[0:1] Name by which this datum is identified. The geodetic datum is associated with the coordinate reference system and indicates the shape and size of the rotation ellipsoid and this ellipsoid's connection and orientation to the actual globe/earth. It needs to be provided, if the Name identifier does not unambiguously define the geodetic datum as well.
EXAMPLE  geodetic datums include:
  • ED50
  • EUREF89
  • WSG84
X
4VerticalDatumIfcIdentifier[0:1] Name by which the vertical datum is identified. The vertical datum is associated with the height axis of the coordinate reference system and indicates the reference plane and fundamental point defining the origin of a height system. It needs to be provided, if the Name identifier does not unambiguously define the vertical datum as well and if the coordinate reference system is a 3D reference system.
EXAMPLE  vertical datums include:
  • DHHN92: the German 'Haupthöhennetz'
  • EVRS2007; the European Vertical Reference System
X
HasCoordinateOperationIfcCoordinateOperation
@SourceCRS		S[0:1]Indicates conversion between coordinate systems. In particular it refers to an IfcCoordinateOperation between this coordinate reference system, and another Geographic coordinate reference system.X
IfcProjectedCRS
5MapProjectionIfcIdentifier[0:1] Name by which the map projection is identified.
EXAMPLE  map projects include:
  • UTM
  • Gaus-Krueger
X
6MapZoneIfcIdentifier[0:1] Name by which the map zone, relating to the MapProjection, is identified.
EXAMPLE 
  • for UTM, the zone number, like 32 for UTM32
  • for Gaus-Krueger, the zones of longitudinal width, like 3'
X
7MapUnitIfcNamedUnit[0:1] Unit of the coordinate axes composing the map coordinate system.
NOTE  Only length measures are in scope and all two or three axes of the map coordinate system shall have the same length unit.
X
Formal representations
XSD Specification
 <xs:element name="IfcProjectedCRS" type="ifc:IfcProjectedCRS" substitutionGroup="ifc:IfcCoordinateReferenceSystem" nillable="true"/>
 <xs:complexType name="IfcProjectedCRS">
  <xs:complexContent>
   <xs:extension base="ifc:IfcCoordinateReferenceSystem">
    <xs:sequence>
     <xs:element name="MapUnit" type="ifc:IfcNamedUnit" nillable="true" minOccurs="0"/>
    </xs:sequence>
    <xs:attribute name="MapProjection" type="ifc:IfcIdentifier" use="optional"/>
    <xs:attribute name="MapZone" type="ifc:IfcIdentifier" use="optional"/>
   </xs:extension>
  </xs:complexContent>
 </xs:complexType>
EXPRESS Specification
ENTITY IfcProjectedCRS
 SUBTYPE OF (IfcCoordinateReferenceSystem);
  MapProjection : OPTIONAL IfcIdentifier;
  MapZone : OPTIONAL IfcIdentifier;
  MapUnit : OPTIONAL IfcNamedUnit;
 WHERE
  IsLengthUnit : NOT(EXISTS(MapUnit)) OR (MapUnit.UnitType = IfcUnitEnum.LENGTHUNIT);
END_ENTITY;

Link to EXPRESS-G diagram EXPRESS-G diagram

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