IFCGEOMETRICCONSTRAINTRESOURCE
The data model consists of the following:
The schema IfcGeometricConstraintResource
defines the resources used to determine the placement of the shape
representation of a product within the geometric representation context
of a project. It also contains resource definitions to be assigned to
product connectivity definitions to determine the connection geometry
constraints between those products.
The primary application of this resource is to:
 determine the object placement used for the shape
representation of the object
 determine the constraints applied to the connectivity
between two shapes of objects
Placement
The placement of an product's shape is given by the IfcObjectPlacement,
referred to by the IfcProduct.ObjectPlacement. The
object placement defines the object coordinate system in which all
shape representations of that product are defined. It is given either as
 absolute placement
 relative placement
 placement relative to a grid
The absolute placement is specified by using IfcLocalPlacement
and omitting the PlacementRelTo attribute. The
relative placement is specified by using IfcLocalPlacement
and pointing the PlacementRelTo attribute to an IfcObjectPlacement
used in another IfcProduct instance.
A placement relative to a grid is given by IfcGridPlacement
pointing to one (or two) virtual intersections of IfcGridAxis.
If two virtual intersections are references, than the second virtual
intersections specifies the orientation of the object placement.
Connection geometry
The connection geometry constrains the connectivity between
the shapes of two products. The constraint can be defined by geometric
representation items:
or by topological representation items with associated
geometry:
 vertex point
 edge curve
 face surface
As a special type of point connection includes the provision
to express an eccentricity, i.e. a physical distance between the two
points involved in the connection.
Interfaced schemas (8):


(

IfcPoint, IfcBoundedCurve, IfcSurface, IfcCurve, IfcAxis2Placement, IfcLine, IfcConic, IfcPolyline, IfcTrimmedCurve, IfcCompositeCurve, IfcBSplineCurve);



Entities (11):
Select types (3):
Functions (1):