CATIA V5: Surface Continuity Explained

Many of today’s leading industrial designs are deceivingly simple. They look like simple prismatic shapes but, in fact, they are not.

Take any modern smartphone for example. It can be described as a thin brick that could be modeled by simply extruding and adding radii to. This, however, is not the case. Look at the way the light reflections wrap around the corners. If it were just a brick with fillets applied on the corners and edges, the reflections would not flow so smoothly.

The visible connection between the surfaces is determined by the degree of continuity on the shared edge. While point or tangency continuity is sufficient for most mechanical designs, curvature continuity, or even higher, the rate of curvature continuity, is usually required for visually pleasing industrial designs that involve using polished surfaces, such as in consumer products, marine, automotive, and aerospace.


Point continuity (referred to as G0 condition in CATIA) requires surface contact on the common edge but does not require tangency. I.e., the surfaces share an edge, but usually a sharp edge. Most CATIA designs that do not use fillets or blends result in point continuity between surfaces.

Tangency continuity (G1 condition) requires that the surface boundaries share a common edge with tangency, but curvatures do not match. Engineering fillets in CATIA result in tangency continuity between surfaces.

With curvature continuity (G2 condition), the surface boundaries share a common edge with curvatures matching. Curvature continuity results in a smoother reflection transition from one surface to another, which is required for ‘premium’ products. CATIA tools that enable the user to create curvature-continuous surfaces are Styling Fillet , Fill  , and Blend .

In CATIA surfacing, the degree of continuity can be selected if Supports for the surface are defined.

For example, selecting Supports for the Fill surface enables the Continuity pull-down list, as shown below.

Similarly, if Supports are selected when creating a Blend, the user has the option to define the degree of continuity too.

Surface continuity in CATIA can be analyzed with the Connect Checker tool . In the example below, the tool was used to detect G2 (i.e., curvature) discontinuity on the inner edge of the surface.