Represent Shell Based Surface Model

Overview

Identifies the information requirements for provision of a 3D shell based planar surface model shape.
A shell based surface model is described by a set of shells. A shell defines a boundary (closed shell) or a closed shell with holes (open shell).
A shell is defined as a subtype of a connected face set which in turn comprises a set of faces. The connected face set must be defined.
A face in one shell (set of connected faces) may overlap a face in another shell (set of connected faces) if there is a shared intersection. This enables a complete shell based surface model to be described by the boundary determined by a set of shells (connected face sets).

Results

A 3D shell based surface model based is defined.

Description	Entity/Pset/Functional Part	MAN	REC	OPT
Determine the faces to be used in the surface model and bring them into a connected face set. Assign any surfaces that are required within the connected face set.	fp_connected_face_set
Connected face sets are defined by the subtypes closed shell or open shell within a shell based surface model. The faces of the connected face set therefore must be reassigned to the appropriate subtype.	IfcClosedShell.CfsFaces IfcOpenShell.CfsFaces
Assign the shells as a shell based surface model boundary.	IfcShellBasedSurfaceModel.SbsmBoundary
Ensure that the surface model is defined as 3 dimensional by setting the value of the dimensioning attribute to 3	IfcShellBasedSurfaceModel.Dim

IFC Entities Required

• IfcClosedShell
• IfcGeometricRepresentationItem
• IfcOPenShell
• IfcRepresentationItem
• IfcShellBasedSurfaceModel

IFC Datatypes Required

• IfcDimensionCount

IFC Functions Required

• -

IDM Functional Parts Required

• fp_connect_face_set

EXPRESS-G

EXPRESS Schema

SCHEMA FP_REPRESENT_SHELL_BASED_SURFACE_MODEL;

  TYPE IfcShell = SELECT
    (IfcClosedShell,
     IfcOpenShell);
  END_TYPE;

  TYPE IfcDimensionCount = INTEGER;
    WHERE
      WR1 : { 0 < SELF <= 3 };
  END_TYPE;

  ENTITY IfcGeometricRepresentationItem
    ABSTRACT SUPERTYPE
    SUBTYPE OF(IfcRepresentationItem);
  END_ENTITY;

  ENTITY IfcRepresentationItem
    ABSTRACT SUPERTYPE;
  END_ENTITY;

  ENTITY IfcShellBasedSurfaceModel
    SUBTYPE OF(IfcGeometricRepresentationItem);
      SbsmBoundary : SET [1:?] OF IfcShell;
    DERIVE
      Dim          : IfcDimensionCount := 3;
  END_ENTITY;

  ENTITY IfcClosedShell
    SUBTYPE OF(fp_connect_face_set);
  END_ENTITY;

  ENTITY fp_connect_face_set
    SUPERTYPE OF (ONEOF(IfcClosedShell, IfcOpenShell));
  END_ENTITY;

  ENTITY IfcOpenShell
    SUBTYPE OF(fp_connect_face_set);
  END_ENTITY;

END_SCHEMA;