A smooth constraint forces a spline to maintain geometric continuity with another spline, line, arc, or polyline.
In the example below, a smooth constraint has been applied to the two spline curves on the left. The result is the block definition on the right, where the spline curves are joined continuously.
Manipulate a Smooth Constraint
When you manipulate a block with a smooth constraint applied, the constrained objects will always maintain fluid continuity.
In the example below, the two spline curves on the left have a smooth constraint applied. The geometry of the spline curves on the right has been changed, but they retain a fluid continuity.