Description: 10 minutes
You can specify a connect condition between a curve and an edge or face when creating or modifying a 3D curve. These connect conditions are either tangential or curvature continuous. The tangent or curvature value defined at the point on the edge or face defines the tangent or curvature of the curve to be created or modified.
If the curve is flat, the curvature radius is big. If the curve turns strongly, the curvature radius is small. A straight line has an infinite radius. A circle has a constant curvature radius equal to the circle radius.

Top curve is flat with a big radius. Bottom curve turns and has a small radius.
When you specify a tangential or curvature continuous condition at a specific point, the new curve will be tangential or curvature continuous at that point. The tangent or the tangent and curvature will be smooth. If only a tangential condition is specified, the curvature will not be smooth.
![]() Tangential condition - Maintain the same tangent direction. |
![]() Curvature continuous condition - Maintain the same tangent direction and the same curvature radius. |
Use tangential or curvature continuous condition to create smooth connections between curves.
To visualize the curvature (radius), use the Curve Analysis function.

In this example of Curve Analysis, the top curve is a circle and either side is a curve connected to the circle. The curve on the left was connected with a curvature continuous condition. The smooth connection is shown by the way the red lines continue uninterrupted from one curve to the next. The curve on the right was connected with a tangential condition and shows a less smooth connection. The analysis conveys a jump in the curve by the way the red lines from the side curve do not match the red lines from the top curve.