Click the icon and then click on any control point in one of the orthogonal projection views. A column of control points will be inserted before the column corresponding to the clicked point.

The control points in the new column will be inserted at coordinates linearly interpolated from the control points on columns immediately before and immediately after the new column. For this reason, inserting a new column after the last column is not permitted.

Switch between orthogonal projection views and continue inserting columns.