IfcGeometricRepresentationContext
Definition
from ISO/CD 10303-42:1992: A
geometric representation context is a representation context in which
the geometric representation items are geometrically founded. A
geometric representation context is a distinct coordinate space,
spatially unrelated to other coordinate spaces.
Definition
from IAI: The IfcGeometricRepresentationContext
defines the context that applies to several shape representations of
products within a project. It defines the type of the context in which
the shape representation is defined, and the numeric precision
applicable to the geometric representation items defined in this
context. In addition it can be used to offset the project coordinate
system from a global point of origin, using the WorldCoordinateSystem
attribute. The TrueNorth attribute can be given,
if the y axis of the WorldCoordinateSystem does not
point to the global
northing.
NOTE: The inherited attribute ContextType
shall have one of the following recognized values: 'Sketch',
'Outline', 'Design', 'Detail', 'Model',
'Plan',
'NotDefined'.
The use of one instance of IfcGeometricRepresentationContext
to represent the model (3D) view is mandatory, the use of a second
instance of IfcGeometricRepresentationContext
to represent the plan (2D) view is optional (but needs to be given, if
there are scale dependent plan views), the additional scale or view
dependent contexts need to be handled by using the subtype IfcGeometricRepresentationSubContext
pointing to the model view (or the plan view) as the ParentContext.
NOTE
The definition
of this class relates to the STEP entity
geometric_representation_context. Please refer to ISO/IS 10303-42:1994
for the final definition of the formal standard.
HISTORY
New Entity in IFC Release 2.0
IFC2x Edition 3 CHANGE The
attribute WorldCoordinateSystem has been
made OPTIONAL Applicable values for ContextType
are only 'Model', 'Plan', and 'NotDefined'. All other sub contexts
are now handled by the new subtype in IFC2x Edition 2 IfcGeometricRepresentationSubContext.
Upward compatibility for file based exchange is guaranteed.
EXPRESS specification:
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| ENTITY IfcGeometricRepresentationContext
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| Precision
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OPTIONAL REAL;
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Attribute definitions:
| CoordinateSpaceDimension
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The integer dimension count of the coordinate space modeled in a geometric representation context.
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| Precision
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Value of the model precision for geometric models. It is a double value (REAL), typically in 1E-5 to 1E-8 range, that indicates the tolerance under which two given points are still assumed to be identical. The value can be used e.g. to sets the maximum distance from an edge curve to the underlying face surface in brep models.
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| WorldCoordinateSystem
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Establishment of the engineering coordinate system (often refered to as the world coordinate system in CAD) for all representation contexts used by the project. If not given, it defaults to origin: (0.,0.,0.) and directions x(1.,0.,0.), y(0.,1.,0.), z(0.,0.,1.).
Note it can be used to provide better numeric stability if the placement of the building(s) is far away from the origin.
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| TrueNorth
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Direction of the true north relative to the underlying coordinate system as established by the attribute WorldCoordinateSystem. It is given by a direction within the xy-plane of the underlying coordinate system. If not given, it defaults to the positive direction of the y-axis of the WorldCoordinateSystem.
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| HasSubContexts
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The set of IfcGeometricRepresentationSubContexts that refer to this IfcGeometricRepresentationContext.
IFC2x Edition 3 CHANGE New inverse attribute.
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Inheritance graph
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| ENTITY IfcGeometricRepresentationContext;
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| Precision
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OPTIONAL REAL;
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