## 8.9.2.4 IfcBSplineSurfaceForm

### 8.9.2.4.1 Semantic definitions at the entity

The *IfcBSplineSurfaceForm* represents a part of a surface of some specific form.

NOTE Definition according to ISO/CD 10303-42:1992

This type is used to indicate that the B-spline surface represents a part of a surface of some specific form.

NOTE Type adapted from **b_spline_surface_form** defined in ISO 10303-42.

HISTORY New type in IFC4.

#### Items

##### PLANE_SURF

A bounded portion of a plane represented by a B-spline surface of degree 1 in each parameter.

##### CYLINDRICAL

##### CONICAL_SURF

A bounded portion of the surface of a right circular cone.

##### SPHERICAL_SURF

A bounded portion of a sphere, or a complete sphere, represented by a B-spline surface.

##### TOROIDAL

##### SURF_OF_REVOLUTION

A bounded portion of a surface of revolution.

##### RULED_SURF

A surface constructed from two parametric curves by joining with straight lines
corresponding points with the same parameter value on each of the curves.

##### GENERALISED_CONE

A special case of a ruled surface in which the second curve degenerates to a
single point; when represented by a B-spline surface all the control points along one edge will be coincident.

##### QUADRIC_SURF

A bounded portion of one of the class of surfaces of degree 2 in the variables x, y and z.

##### SURF_OF_LINEAR_EXTRUSION

A bounded portion of a surface of linear extrusion represented by a B-spline surface of degree 1 in one of the parameters.

##### UNSPECIFIED

A surface for which no particular form is specified.

### 8.9.2.4.1 Formal representations

TYPE IfcBSplineSurfaceForm = ENUMERATION OF
(PLANE_SURF
,CYLINDRICAL_SURF
,CONICAL_SURF
,SPHERICAL_SURF
,TOROIDAL_SURF
,SURF_OF_REVOLUTION
,RULED_SURF
,GENERALISED_CONE
,QUADRIC_SURF
,SURF_OF_LINEAR_EXTRUSION
,UNSPECIFIED);
END_TYPE;