About Boundary Blend Control Points
You can control the shape of a surface by using boundary blend control points. Blend control points allow you to create surfaces with an optimal number of edges and surfaces. By eliminating unnecessary small surfaces and extra edges, you can achieve a smoother surface shape and avoid undesirable twisting and stretching of surfaces.
You can specify points to be connected with each other for curves in each direction. Two types of points can be selected as control points:
Vertices of the datum curves or edges used to define the boundary
Datum points that lie on the curve
Right-click and choose Next Chain on the shortcut menu to leave the control point for a curve undefined and skip to the next curve. The system assigns a sequential number for each set of blend control points.