Class TIfcDerivedUnit

Unit

Declaration

type TIfcDerivedUnit = class(TIfcUnit)

Description

A derived unit is a unit that is formed from an expression of other units.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4538).

Hierarchy

Show Additional Members:

Overview

Methods

Protected function WantsGlobalId: Boolean; virtual;
Protected class function IfcClassName: String; virtual;
Public constructor Create(AOwner: TComponent); override;
Public destructor Destroy; override;

Properties

Published property GlobalId: String read FGlobalId write FGlobalId;
Published property Elements: TIfcDerivedUnitElementList read FElements;
Published property UnitType: TIfcDerivedUnitEnum read FUnitType write FUnitType;
Published property UserDefinedType: TIfcLabel read FUserDefinedType write FUserDefinedType;
Published property Name: TIfcLabel read FName write FName;

Description

Methods

Protected function WantsGlobalId: Boolean; virtual;

This item is declared in ancestor TIfcPersistent.

If True, instances of this class will have GlobalId auto-assigned at saving, and they will be saved as part of the "data" list in IFC JSON files.

Strictly following the spec, this should be only defined for TIfcRoot, because only IfcRoot has GlobalId. In reality, we need GlobalId at TIfcPersistent to load some files, and we sometimes need WantsGlobalId = True to save some files.

Source: scene/load/ifc/castleifc_ifc_types.inc (line 52).

Protected class function IfcClassName: String; virtual;

This item is declared in ancestor TIfcPersistent.

Name for the IFC standard, used in IFC files. By default, this is just ClassName with prefix 'T' removed.

Source: scene/load/ifc/castleifc_ifc_types.inc (line 56).

Public constructor Create(AOwner: TComponent); override;

This item has no description.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4545).

Public destructor Destroy; override;

This item has no description.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4546).

Properties

Published property GlobalId: String read FGlobalId write FGlobalId;

This item is declared in ancestor TIfcPersistent.

Globally unique identifier for the object instance.

Note: Not declared as TGUID, because TGUID cannot be published, but also we don't really need it: for our purposes, this identifier is just an arbitrary string.

Note: IFC 4.3 specification puts this only at IfcRoot, not at every IFC class. But testcase https://github.com/buildingsmart-community/Community-Sample-Test-Files/blob/main/IFC%204.0.2.1%20(IFC%204)/ISO%20Spec%20archive/wall-with-opening-and-window.json (from IFC 4.0) shows this can be present at any IFC class, in particular TIfcGeometricRepresentationContext.

In fact, TIfcGeometricRepresentationContext needs to have GlobalId to be successfully saved (avoid recursively trying to serialize it) in some cases. We indicate such classes with WantsGlobalId.

IFC JSON documentation says this, which seems to (unfortunately it is not unambiguous enough...) allow this at any IFC class: "Whereas the globalId attribute is only available to those elements that are descendent of the IfcRoot entity in the EXPRESS schema, we encourage a broader use of this globalId, to enable referencing between objects in a JSON file when useful.".

Source: scene/load/ifc/castleifc_ifc_types.inc (line 79).

Published property Elements: TIfcDerivedUnitElementList read FElements;

The group of units and their exponents that define the derived unit.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4549).

Published property UnitType: TIfcDerivedUnitEnum read FUnitType write FUnitType;

Type of the derived unit chosen from an enumeration of derived unit types for use in IFC models.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4553).

Published property UserDefinedType: TIfcLabel read FUserDefinedType write FUserDefinedType;

Type of the derived unit if the UnitType attribute is set to UserDefined.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4556).

Published property Name: TIfcLabel read FName write FName;

Name of the unit in addition to the unit type, particularly when the derived unit elements refer to conversion or context based units.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4560).


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