Reshaping Regions of Curves and Surfaces

Transforms a specified region on a curve or a surface without the transformation being applied to, or affecting, any area outside of this region.

For example, you can create controlled contortions to a surface representing recesses.

How to Use

1

Select Proportional mod- from the Xform > Modify cascading menu, or double-click its icon. The Pmod Control window appears (see page 197) and the system prompts:

Select the primary CV.

2

Click a CV on the curve or the surface in the center of the region that you want to modify. A locator appears to identify the primary CV. (See the example on the left.)

3

The system prompts:

Enter MOVE amounts (x,y,z) (ABS):

Either type the move coordinates at the keyboard, or drag the CV using the mouse. The object changes shape according to how you move the CV.

4

Undo your changes at any time (while the CV is still selected), by clicking on the Revert button at the bottom of the control window.

5

Determine how many additional CVs (preceding and following the primary CV in both the U and V directions) should be included to define the surface region affected by the modification.

Use the Preceding U/V and Succeeding U/V sliders in the Pmod Control window to set these values. (In the example on the left, we set Preceding# U = 1 and Preceding# V = 1)

The corresponding CVs are highlighted to show that they have been selected and will be affected by further modifications.

Proportional Modifications Options

Select Xform > Modify > Proportional mod- to display the Proportional Modification Options window.

Operations

The type of modification performed depends on the current Operations option setting.

See:
Moving Objects on page 176, Rotating Objects on page 180, and Changing the Dimensions of Objects on page 185.

Move, Rotate , and Nonp-Scale

Operate in the same way as the standard Xform > Move, Xform > Rotate and Xform > Nonp scale functions. You can perform the modification with the mouse or with the keyboard, in absolute or relative addressing mode.

Smooth

Performs an interpolation based on the current Degree # values for averaging the CVs in the region of effect.

No interaction beyond selecting the primary CV and the region of effect is required when performing smoothing.

NURBS Surface Options

Degree #

The Degree # parameters specify the degree of effect in the U and V parametric directions. The range for these fields is from -5.00 to 5.00.

As the transformation is applied, the amount by which the preceding and succeeding CVs are affected in relation to the primary CV is determined by the current degree value and the distance of each CV from its neighbor. A degree of 0 applies the transformation equally over the affected region.

If this value is positive, the effect of the transformation is decreased for CVs that are further away from the primary CV-the greater the degree, the greater this dampening effect. The greater the number of CVs between the primary CV and the boundary of the defined region, the less of an effect the transformation has on each individual CV.

If the degree is negative, the effect of the transformation is increased for CVs that are further away from the primary CV. The greater the number of CVs between the primary CV and the boundary of the defined region, the greater the effect of the transformation is on each individual CV.

Preceding #

Use these fields to specify the number of CVs preceding the primary CV that you want to include in the region definition along the U and V parametric directions.

The range of preceding CVs that can be affected by the operation ranges from 0 (the default) to N, where N is the maximum possible number of CVs in the given direction for the particular object. Hence, to select all CVs in a particular direction, simply drag the slider all the way to the right.

Succeeding #

Use these fields to specify the number of CVs succeeding the primary CV that you want to include in the region definition along the U and V parametric directions.

The range of succeeding CVs that can be affected by the operation ranges from 0 (the default) to N, where N is the maximum possible number of CVs in the given direction for the particular object. Hence, to select all CVs in a particular direction, simply drag the slider all the way to the right.

Polygon Surface Options

If you click on the Polygonal Surface Options title, the following set of options appears:

Polyset Modification Type

Choose By Parameterization to modify the polyset based on texture coordinate parameterization, or By Geometry to modify it based on topology.

This option only appears when Polyset Modification Type is set to By Parameterization.

Include polyset edge

This toggle specifies whether polyset vertices that exactly equal the endpoints of the range specified by the Preceding and Succeeding polyset range options should be included in the proportional modification.

The default values for these settings cause the entire surface to be proportionally modified.

These options only appear when Polyset Modification Type is set to By Parameterization.

Preceding/Succeeding polyset range

These slider values represent the range of polyset vertices that should be included in a proportional modification. The amount of modification applied to an individual polyset vertex depends on its S and T (also known as texture) coordinate values.

On most polygonal surfaces, these values form a two-dimensional parameterization of the surface.

The Preceding slider indicates what percentage of vertices with coordinates (either S or T) less than that of the target vertex should be proportionally modified.

The Succeeding slider indicates what percentage of vertices with coordinates (either S or T) greater than that of the target vertex should be proportionally modified.

These four options only appear when Polyset Modification Type is set to By Geometry.

Extent Shape

Choose Sharp for a sharp drop-off, or Round for a smoother drop-off.

Degree

Specify the degree of change as a function of the distance from the primary vertex. This option behaves the same as Degree# for NURBS geometry (see page 197).

Extent Measurement

Choose either Edges or Polygons as the unit of measure for the Extent (see below).

Extent

Specify how many units (i.e. edges or polygons - see above) from the primary vertex will be affected by the modification. If set to 0, only the primary vertex is modified. The default is 5.

Revert button

This button, located at the bottom of the control window, allows you to undo all your modifications since the currently active CVs were selected.

Notes

• If using Proportional mod on faces, only the outline of the face or any one hole can be modified at a time. Additionally, remember that a face must be co-planar at all times.

For information on faces, see the NURBS Modeling manual.

• Do not use Proportional mod to effect a change on a face that would result in the face no longer being co-planar.

• This function only affects the location of CVs, and not the transformation matrix of the surface at the node above the geometry.