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.
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. |
| 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. |
| 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. |
| 5 | MapProjection | OPTIONAL IfcIdentifier |
Name by which the map projection is identified. |
| 6 | MapZone | OPTIONAL IfcIdentifier |
Name by which the map zone, relating to the MapProjection, is identified. |
| 7 | MapUnit | OPTIONAL IfcNamedUnit |
Unit of the coordinate axes composing the map coordinate system. |
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;