Class TIfcMeasureWithUnit

Unit

Declaration

type TIfcMeasureWithUnit = class(TIfcPersistent)

Description

This has two usages:

1. For representing measure value together with its unit on the entity type attribute level; thus overriding the IFC model global unit assignments.

2. For conversion based unit to give the conversion rate and its base.

Spec: https://standards.buildingsmart.org/IFC/RELEASE/IFC4_3/HTML/lexical/IfcMeasureWithUnit.htm

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4731).

Hierarchy

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Overview

Methods

Protected function WantsGlobalId: Boolean; virtual;
Protected class function IfcClassName: String; virtual;

Properties

Published property GlobalId: String read FGlobalId write FGlobalId;
Published property ValueComponent: TIfcValue read FValueComponent write FValueComponent;
Published property UnitComponent: TIfcUnit read FUnitComponent write FUnitComponent;

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).

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 ValueComponent: TIfcValue read FValueComponent write FValueComponent;

Value of the physical quantity when expressed in the specified units.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4737).

Published property UnitComponent: TIfcUnit read FUnitComponent write FUnitComponent;

The unit in which the physical quantity is expressed.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 4740).


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