8.18.3.11 IfcProjectedCRS
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:
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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.
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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.
The code 'EPSG:5555' identifies the combination of ETRS89 / UTM zone 32N + DHHN92 height (i.e., a projected CRS + a vertical CRS). The code 'EPSG:6258' identifies the geodetic datum of the projected CRS ETRS89 / UTM zone 32N (itself identified as EPSG:25832). The code 'EPSG:5181' identifies the vertical datum of the vertical CRS DHHN92 height (itself identified as EPSG:5783). 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. New entity in IFC4.8.18.3.11.2 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. 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'. 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. 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. geodetic datums include: |
| 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. |
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| Click to show 5 hidden inherited attributes Click to hide 5 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. 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. map projections include: UTM; Gauss-Krueger |
| 6 | MapZone | OPTIONAL IfcIdentifier |
Name by which the map zone, relating to the MapProjection, is identified. 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. Only length measures are in scope and all two or three axes of the map coordinate system shall have the same length unit. If MapUnit is omitted, the unit for the coordinate axes is taken from the default units, as stated in IfcProject.UnitInContext. |
8.18.3.11.4 Formal propositions
| Name | Description |
|---|---|
| MapUnitIsLength |
No description available. |
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8.18.3.11.5 Examples
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;