REVIT IFC MANUAL
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10 | Autodesk Revit <strong>IFC</strong> manual<br />
2.4.2 Geometric representation of <strong>IFC</strong> objects<br />
There are three basic possibilities for geometrically representing a three-dimensional <strong>IFC</strong> object:<br />
- extrusions<br />
- solid body representation using a sweep, and<br />
- representation using B-reps.<br />
Extrusions<br />
Are the most common and simple graphical method and are used for most of the cases when the shape<br />
can be described by a simple profile.<br />
Swept solids<br />
As the name implies, an element is created with the swept solid<br />
method using a sweep. In this case, a defined profile is led along a<br />
path (direction vector) to generate the solid. This profile may change<br />
due to rotation or distortion along the path. Revit uses this method<br />
for describing rebar and other shapes which cannot be described<br />
with extrusions.<br />
B-rep<br />
The method known as boundary representation (B-rep) can also be<br />
described as a boundary surface model. The surfaces of a component<br />
are represented using coordinates and together form the actual solid,<br />
allowing even complex forms to be represented.<br />
B-rep objects use complex calculations to represent individual<br />
surfaces in detail, and thus use more data memory.<br />
NURBS and other smooth surfaces<br />
In the <strong>IFC</strong>4 schema, it is possible to generate B-rep objects as<br />
advanced B-reps using NURBS (non-uniform rational B-splines)<br />
surfaces. The memory space required is thus drastically reduced,<br />
while the bodies are represented more accurately.<br />
INSTRUCTIONS FOR <strong>REVIT</strong> USERS
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