The Compact function is used when you wish to position one or more control points precisely over an existing control point. This can be used to create a knuckle or discontinuity in the surface or to collapse a side to a point e.g. at the bottom of a bow cone (see Discontinuities and Feature Lines on page 137).

 This video shows how a knuckle can be created in a curve by compacting control points. This video also shows the advantage of grouping compacted control points together.

 View a video that shows how to model a chine or knuckle line in a surface by compacting control points.

To compact two or more control points

§   Select one control point,

This control point is the one that you wish all other control points to compact onto. It will remain stationary when you select the Compact function.

§   Hold down the Shift key and select one or more other control points.

These are the control points that you wish to compact to the first selected control point.

§   Select Compact from the Controls menu or type Ctrl+K.

This will compact all selected control points to the first selected point.

Note:

The Compact command does not hold the compacted points together permanently, i.e. if you select one with the mouse and move it, the other points in the same position will not move with it. If you wish all the points to move as one, select all the compacted points (with a selection box) and then select the Group command.

It is possible to use compacted grouped control points as a means of introducing a discontinuity into a surface.

Consider a surface whose stiffness is set to flexible (order 3) in the transverse (column) direction. The following example shows how the use of two rows of control points can form a discontinuity in the surface.

Illustrated below is a Perspective view of the net and shape of a simple surface.

If an additional control point row is added, and its points compacted directly on top of the existing intermediate control point row, a hard corner is created running along the surface, as shown in the following illustration.

The scope of the discontinuity may be changed by splitting the superimposed row in some of the columns.

By splitting the row at the right hand edge of the surface as shown it is possible to fade the hard edge out. The surface shows a smoothly curved section at its right hand edge and a section with a hard corner at its left hand edge.

To achieve a discontinuity of this type you need to compact several control points together. The number of points required to achieve a hard corner is always one less than the order of the surface in that direction. For example, if you have a surface that is flexible in the transverse direction (Order 3), you will only need to superimpose two control points to achieve a hard corner in the section. If, on the other hand, the transverse stiffness is set to stiff (Order 6), five control points will need to be compacted together to form the corner.

If you wish to display the line along the corner you have created, select Feature Lines from the Contours menu item. The effect will be similar to the following:

Note:

Do not compact more control points than necessary to create a knuckle. The required number of control points is the surface stiffness minus 1. For example: a stiffness 4 surface requires 3 compacted control points to create a knuckle.

See also Grouping Control Points on page 138.