Curve Controls

The Effect->Curve Controls command in the Model module allows you to modify a curve or surface along in its u and/or v directions.

You can use combinations of curve control modifications to achieve very different looks for curves and surfaces. For example, the effect of shifting v on a surface is quite different depending on whether the surface is closed or open in the v direction. The interactive dialogue box allows you to see these effects immediately.

Uses

By default, a curve is closed/open at the starting point in u. Similarly, a surface object can be closed or opened at the starting rows in u or v.

If you wish to modify the point at which the curve or surface opens, choose Effect->Curve Controls and use the Shift U option to shift the starting point of the curve or surface.

It is also useful when skinning curves or merging surface objects.

For more information and examples using this command, see the Shifting the Starting Point of a Curve section and Inverting the Direction of a Curve of the Modelling User's Guide.

Procedure

1. Select a closed curve or surface object.
2. Choose the Effect->Curve Controls command.
   
   The Curve Controls dialogue box is displayed.
   
   The u direction is highlighted by a red edge flag on the object, and the v direction is highlighted by a green edge flag.
   
   
3. Set the curve control parameters as desired. The results are displayed interactively.
4. Click Ok to accept the settings or Cancel to exit the dialogue box.

Parameters

Shift U, V

Interactively offsets the starting point of a curve, or the starting row (edge flags) of a surface.

The control points are preserved, yet the shape of the resultingcurve or surface looks very different as you offset the starting point in either direction, just as a connect-the-dots picture would look very different if you started connecting at a different dot each time.

Close U, V

These values reflect the values selected in the Info->Selection dialogue box; if an option is selected in the Curve Controls dialogue box, it means the direction was already closed. However, by altering these settings in the Curve Controls dialogue box, the change is reflected in the Info Selection dialogue box.

Inverse U, V

The direction of surface normals is determined by the increasing direction in u and in v. When you click Inverse U or Inverse V, you reverse the increasing direction of the selected direction, thereby reversing the surface normals and changing the rendered image of the surface.

For example, extrude a curve and look at in Shade view. Choose Effect->Curve Controls and then click Inverse U. If you looked at the extrusion again in Shade, it would be shaded differently.

Note:
Inverse U has the same effect as the Effect->Inverse command.

Swap U & V

This operation reverses the u and v directions along the surface.

Last updated 02-apr-1998