8.18.3.11 IfcProjectedCRS

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AbV ⓘ

8.18.3.11.1 Semantic definition

IfcProjectedCRS is a coordinate reference system (CRS) of the map to which the map translation of the local engineering coordinate system of the construction or facility engineering project relates. 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 to determine the length unit used by the map.

Despite what its name suggests:

If the referenced IfcGeometricRepresentationContext is 3D, then IfcProjectedCRS shall be a compound coordinate reference system, meaning a combination of multiple CRS from which a GeodeticDatum and a VerticalDatum can always be unambiguously identified.
If the referenced IfcGeometricRepresentationContext is 2D, then IfcProjectedCRS can be either a projected coordinate reference system or a compound coordinate reference system.

The unambiguous identifier by which the coordinate reference system is known, is stored in the inherited Name attribute. Well defined identifiers include the map projection, the map zone information, and all required datums. In these cases the attributes VerticalDatum, MapProjection, MapZone as well as the inherited attribute GeodeticDatum can be omitted.

8.18.3.11.2 Entity inheritance

8.18.3.11.3 Attributes

#	Attribute	Type	Description
IfcCoordinateReferenceSystem (5)
1	Name	OPTIONAL IfcLabel	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 namespace, for example as 'EPSG:5555'. NOTE The Name shall contain only one EPSG code. When there is not one EPSG that unambiguously identifies the CRS, IfcWellKnownText shall be used. Combining multiple EPSG codes in one string for Name (e.g., 'EPSG:2056,EPSG:5728') is not allowed. NOTE The name shall be 'WKT' if an EPSG code does not exist for the coordinate reference system (CRS). In this case, the CRS shall be further specified using the IfcWellKnownText entity.
2	Description	OPTIONAL IfcText	Informal description of this coordinate reference system.
3	GeodeticDatum	OPTIONAL IfcIdentifier	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: EPSG:6326 (WGS84 World Geodetic System 1984, used in GPS); ED50 (European Datum 1950, also identified as EPSG:6230); EUREF89 (European Terrestrial Reference Frame 1989, also identified as EPSG:1178).
	HasCoordinateOperation	SET [0:1] OF IfcCoordinateOperation FOR SourceCRS	Indicates conversion between coordinate reference systems. In particular it refers to an IfcCoordinateOperation between this coordinate reference system, and another coordinate reference system.
	WellKnownText	SET [0:1] OF IfcWellKnownText FOR CoordinateReferenceSystem	Well Known Text (WKT) definition for this coordinate reference system inversely associated as a IfcWellKnownText entity.
Click to show 5 hidden inherited attributes
IfcProjectedCRS (4)
4	VerticalDatum	OPTIONAL IfcIdentifier	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: 'EPSG:5181' (Deutsches Haupthöhennetz 1992); 'EPSG:5215' (European Vertical Reference Frame 2007)
5	MapProjection	OPTIONAL IfcIdentifier	Name by which the map projection is identified. EXAMPLE map projections include: UTM; Gauss-Krueger
6	MapZone	OPTIONAL IfcIdentifier	Name by which the map zone, relating to the MapProjection, is identified. EXAMPLE map zones includes: for UTM, the zone number, like 32 for UTM32; for Gauss-Krueger, the zone number, like 3 for GK3
7	MapUnit	OPTIONAL IfcNamedUnit	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. NOTE If MapUnit is omitted, the unit for the coordinate axes is taken from the default units, as stated in IfcProject.UnitInContext.

Table 8.18.3.11.D

8.18.3.11.4 Formal propositions

Name	Description
MapUnitIsLength	No description available.
`NOT(EXISTS(SELF.MapUnit)) OR (SELF.MapUnit.UnitType = IfcUnitEnum.LENGTHUNIT)`

Table 8.18.3.11.E

8.18.3.11.5 Examples

Figure 8.18.3.11.A

Linear Placement Of Signal
Figure 8.18.3.11.B

Geographic Referencing Gk
Figure 8.18.3.11.C

Geographic Referencing Utm

8.18.3.11.6 Formal representation

 ENTITY IfcProjectedCRS
 SUBTYPE OF (IfcCoordinateReferenceSystem);
	VerticalDatum : OPTIONAL IfcIdentifier;
	MapProjection : OPTIONAL IfcIdentifier;
	MapZone : OPTIONAL IfcIdentifier;
	MapUnit : OPTIONAL IfcNamedUnit;
 WHERE
	MapUnitIsLength : NOT(EXISTS(SELF.MapUnit)) OR (SELF.MapUnit.UnitType = IfcUnitEnum.LENGTHUNIT);
END_ENTITY;

8.18.3.11.7 References

IfcCoordinateReferenceSystem