7

Editing Curves

In This Section:

• Adding Points to a Curve 162
• Changing the Weight of CVs 164
• Making Sharper Bends in Curves with Multiplicity 165
• Editing Keypoint Curves 167
• Stretching Curves 170
• Making Curves Intersect 172
• Using the Curve Editor 178
• Creating Continuity Between Curves and Other Objects 182
• Rebuilding Complex Curves 190
• Flattening Curves onto a Plane 198

See also Creating Curves from Other Curves on page 201.

Curve Edit Palette Summary

Icon	Curve Edit >	For more information ...
	Modify > Curve Editor	Using the Curve Editor on page 178
	Modify > Add points	Adding Points to a Curve on page 162
	Modify > Adjust weight	Changing the Weight of CVs on page 164
	Modify > Multiplicity	Making Sharper Bends in Curves with Multiplicity on page 165
	Modify > Adjust intersection	Making Curves Intersect on page 172
	Modify > Stretch	Stretching Curves on page 170
	Create > Duplicate curve	Duplicating Curves on page 202
	Create > Combine curves	Projecting Two Planar Curves into a 3D Curve on page 205
	Create > Fillet curves	Adding a Fillet Between Curves on page 207
	Project tangent	Creating Continuity Between Curves and Other Objects on page 182
	Cut/Join > Break curve at keypoint Cut/Join > Join curves	Cutting and Joining Keypoint Curves on page 211
	Cut/Join > Delete segment	Deleting a Segment of a Curve on page 214
	Cut/Join > Break curve at inflections	Detaching a Curve at the Points of Inflection on page 213
	Rebuild curve	Rebuilding Complex Curves on page 190
	Curve precision	Changing the Display Precision of Objects on page 53
	Curve planarize	Flattening Curves onto a Plane on page 198
	Curve section	Sectioning Curves on page 215

Adding Points to a Curve

Purpose

Add points to the beginning or end of a completed curve.

How To

To add points to one end of an existing curve:

1

Pick the first or last CV or edit point to extend the curve.

• Picking the first point will extend the curve from the beginning. Picking the last point will extend the curve from the end.

• If you pick a CV (Pick > Point Types > CV), you will extend the curve by adding CVs. If you pick an edit point (Pick > Edit point), you will extend the curve by adding edit points.

2

Click the Modify > Add points icon, or choose Modify > Add points from the Curve Edit palette menu.

The Add points tool highlights the end of the curve.

3

Click to place the new points. You can continue to move the new point while the mouse button is down. When you release the mouse button, the new point is added to the curve.

• Click the left mouse button to place a point.

• Click the middle mouse button to align the point horizontally to the previous one.

• Click the right mouse button to align the point vertically to the previous one.

• Type a 3D coordinate to place a point exactly.

• Use the snapping modifier keys or buttons to snap to the grid or existing parts of the model. See Snapping to Grids, Curves, and Points on page 35.

4

Choose another tool to finish adding points.

Tips and Notes

• Add points does not actually add points to the beginning of a curve. If you have picked the first CV or edit point, the tool reverses the curve and then adds the new points to the end.

• In orthographic windows, the new points will be in the same plane as the previous point, unless you use curve or magnet snapping.

• If you use the Add points tool when an entire curve is selected, it will add CVs to the end of the curve.

See Also

• Drawing Curves on page 128

Changing the Weight of CVs

Purpose

Control the shape of a curve by adjusting the weight of a CV (the amount the CV pulls the curve from a straight line).

How To

To change the weight of CVs:

1

Use Pick > Point Types > CV to pick all the CVs you want to modify.

2

Click the Adjust weight icon, or choose Modify > Adjust weight from the Curve Edit palette menu.

• Drag the mouse left and right to set the weight interactively.

• Type a value from 0.0001 to 10 000.0 to set the weight exactly.

Important

• Some other software package cannot import Alias wire files with adjusted CV weights.

• Changing the weighting of CVs will increase render times.

• In practice, trying to model by weighting CVs is difficult and usually not worth the effort on a large scale.

Tips and Notes

• To see the current weighting factor of a CV, pick the CV and open the Information Window.

• Curves are created with all CV weights set to 1.0.

See Also

CVs on page 8, and Rational vs. Non-rational Geometry on page 13

Making Sharper Bends in Curves with Multiplicity

Purpose

Change the sharpness of bends in a curve by setting the multiplicity of CVs.

How To

To set the multiplicity of CVs:

1

Use Pick > Point Types > CV to pick all the CVs you want to modify.

2

Click the Multiplicity icon, or choose Modify > Multiplicity from the Curve Edit palette menu.

The Multiplicity tool sets the multiplicity of the picked CVs to match the value in the option box (see below).

3

Type a number (1, 2 or 3) to set the multiplicity of the picked CVs.

Important

• Some other software package cannot import Alias wire files with multiplicity.

• Many of the advanced surfacing tools cannot work with curves with multiplicity.

Options

Multiplicity

The initial multiplicity the picked CVs are set to, when the Multiplicity tool is selected.

Tips and Notes

• Often you can achieve the same sharpening effect by placing several CVs close together, without using multiplicity.

• Multiplicity only works on degree 3 curves or surfaces.

See Also

• CVs on page 8

• Multi-knots and CV Multiplicity on page 9

• Degree on page 12

Editing Keypoint Curves

Purpose

Edit keypoint curves by moving the keypoints that define the shape of the curves.

How To

To move a keypoint:

1

Click the Drag keypoints icon, or choose Drag keypoints from the Xform palette menu.

2

Pick a keypoint and drag to move it.

• Remember that you must use snapping to move a point in the perspective window.

• If you drag a line keypoint with the mouse over a guideline, the point is constrained to the guideline.

To edit a keypoint attribute:

1

Choose Windows > Information > Information window to open the Information Window.

2

Pick the curve you want to edit.

3

Open the Attributes (or Ellipse Information) section of the Information Window.

Tips and Notes

• Dragging a part of a keypoint curve that is controlled by an extra attribute will remove the extra attribute.

For example, if you change the angle of a line that was drawn parallel to another line, the Line offset attribute will no longer be available in the Information Window.

• When you join a keypoint curve to a normal curve, keypoints are added to the normal curve. You can drag the keypoints to stretch the curve. The curve shows up as an arc with an Angle/Sweep of zero in the Information Window.

Keypoint Attributes

Curve type	Length/ Radius	Angle/Sweep	Line Offset	Rel Angle	Arc Compl.	Arc Offset	Major Axis	Minor Axis	Sweep
Line	4	4
Parallel Line	4	4	4
Line at Angle	4	4		4
Arc	4	4			4
Circle	4	4
Concentric Arc	4	4				4
Ellipse							4	4	4

Length/Radius

For lines, the length of the line from the start point.

For arcs, the radius.

Angle/Sweep

For lines, the angle from the horizontal axis when it was drawn.

For arcs, the number of degrees of a full circle.

Line Offset

For parallel lines, the distance from the first line (or tangent line if it's a curve).

Rel Angle

For lines drawn at an angle, the relative angle from the first line.

Arc Complement

Click this button to draw the arc in the opposite direction.

Arc Offset

For concentric arcs, the distance from the first arc.

Major Axis

For ellipses, the length of the major axis.

Minor Axis

For ellipses, the length of the minor axis.

Sweep (ellipse)

For ellipses, the Sweep the ellipse was drawn with (set in the options window of the Ellipse tool. See Drawing Keypoint Ellipses on page 157). You cannot edit this attribute.

Stretching Curves

Purpose

Stretch or reshape a curve by moving handles attached to the curve.

How To

To stretch a curve by moving handles:

1

Click the Stretch icon, or choose Modify > Stretch from the Curve Edit palette menu.

2

Click the curve you want to stretch.

3

Handles appear on the curve, regularly spaced between the beginning and end points.

4

Drag a handle to move that part of the curve and stretch the rest of the curve.

To change the location of a handle on the curve:

1

Hold down the Shift key and click a handle to turn it into a locator.

2

Drag the locator along the curve.

3

Click the locator to turn it back into a handle.

To change the number of handles:

1

Double click the Stretch icon, or choose Modify > Stretch- from the Curve Edit palette menu.

2

Set the Number of Points option to the number of handles you want on the curve. You cannot use more handles than the curve's degree + 1. For example, a degree 3 curve cannot have more than 4 handles.

3

Click Go.

4

Click a curve to use the Stretch tool.

Tips and Notes

• The Stretch tool is harder to explain than to use. Try creating a curve and stretching it to see how the tool works.

• You can still use curve, magnet, and grid snapping when moving handles.

• You can use the Information Window to set the parameters of the handles exactly.

• The first and last handles stay locked to their parameters while dragging, even when the Parameter option is set to Floating.

Options

Number of Points

The number of handles (from 2 to 8) on the curve.

You cannot use more handles than the curve's degree + 1. For example, a degree 3 curve cannot have more than 4 handles.

This option is available when the Number of Points is greater than 2.

Parameter

Locked-the handles stay at the same parameter on the curve as they move (default).

Floating-the handles can slide along the curve as you drag it. This option minimizes the changes to the curve from using Stretch. This option does not affect the first and last handles.

See Also

• Scaling Objects in the Basic Tools book.

• Changing the Dimensions of Objects in the Basic Tools book

• Getting Detailed Information in the Basic Tools book

Making Curves Intersect

Purpose

• Modify a curve to intersect another where they cross in a view window, at a specific edit point, or simply at the closest point.

• Check for an intersection between two curves.

Overview

The Adjust intersection tool has many options that let you vary the behavior of the tool from almost automatic to full user control.

Because of this, the procedures in the "How To" section are more a small cookbook of common uses than a complete guide to all that the Adjust intersection tool can do.

The following list explains the types of control available:

1

Decide what to do with the first curve (Modification Mode):

• move the entire curve (Global) to create an intersection,

• deform the curve (Segment) to create an intersection, or

• simply check for an existing intersection (None).

2

If you choose to move or deform the curve, you must decide where exactly the intersection will occur (Intersection Selection):

• at the point where the curves cross visually in the view window (View),

• at the closest point to the second curve (Closest), or

• at a specific edit point on the first (Manual Base) or second (Manual Target) curve.

3

If you choose to deform the curve you must decide which part of the curve will be deformed (Segment Selection):

• the entire curve (Entire Curve),

• a segment of the curve automatically calculated based on the other options (Auto), or

• a segment you choose by picking start and end edit points (Manual).

4

If you choose to deform the curve you must also decide whether the start/end point of the deformed segment (Start/End Modification):

• can move (Free),

• stays fixed (Fixed), or

• stays fixed and maintains its tangent (Tangent Fixed).

How To

To quickly move a curve to intersect another curve:

1

Double-click the Adjust intersection icon, or choose Modify > Adjust intersection- from the Curve Edit palette menu.

2

Set Modification Mode to Global. Set Intersection Selection to

• View if the curves already cross visually in the view window.

• Closest if the curves are already close to the correct intersection.

Then click Go.

3

Click the "base" curve. The Adjust intersection tool will move this curve to intersect the "target" curve.

4

Click the target curve.

5

The Adjust intersection tool moves the base curve and creates an edit point at the new intersection if one does not already exist.

To move a curve to intersect at a specific edit point with another curve:

1

Double-click the Adjust intersection icon, or choose Modify > Adjust intersection- from the Curve Edit palette menu.

If the edit point is on the second (target) curve, use Manual Target instead.

2

Set Modification Mode to Global. Set Intersection Selection to Manual Base. Then click Go.

If you chose Manual Target, click the base curve anywhere.

3

Click an edit point on the base curve. The Adjust intersection tool will move this curve to intersect the target curve at this edit point.

If you chose Manual Target, click an edit point on the target curve. The Adjust intersection tool will move the base curve to intersect this curve at this edit point.

4

Click the target curve.

5

The Adjust intersection tool moves the base curve and creates an edit point on the target curve at the new intersection if one does not already exist.

To deform a curve to intersect another curve at a specific edit point:

1

Double-click the Adjust intersection icon, or choose Modify > Adjust intersection- from the Curve Edit palette menu.

2

Set Modification Mode to Segment. Set Intersection Selection to Manual Target. Set Segment Selection to Manual. Then click Go.

3

Click the base curve.

4

Pick two edit points on the base curve to define the segment that will be deformed to create the intersection.

5

Click an edit point on the target curve. The Adjust intersection tool will deform the base curve to intersect this curve at this edit point.

6

The Adjust intersection tool deforms the segment of the first (base) curve and creates an edit point at the new intersection if one does not already exist.

To check for an intersection between two curves

1

Double-click the Adjust intersection icon, or choose Modify > Adjust intersection- from the Curve Edit palette menu.

2

Set Modification Mode to None. Then click Go.

3

Click one curve, then the other.

4

If an intersection already exists between the two curves, an edit point is inserted on both curves at the intersection (unless one already exists) and the prompt line reads:

Done intersecting.

If no intersection exists, nothing happens. The prompt line reads:

With modification NONE, curves must intersect. No edit points added.

Tips and Notes

• The first (base) curve must be degree 3. The second (target) curve must be degree 1 or degree 3.

Options

Keep Originals

Keep a copy of the original curve before it is modified.

Modification Mode

Control what the tool does with the curves.

Global

Move the first curve so that it intersects the target curve.

Segment

Modify the first curve using the Intersection Selection setting so that it intersects the target curve.

None

If an intersection exists, an edit point is added to both curves at the intersection (unless one already exists). This option does not modify the shape or position of either curve.

These options are available when the Modification Mode is Global or Segment.

Intersection Selection

Manual Base

Asks you to click an edit point on the first (base) curve where the curves will intersect.

Manual Target

Asks you to click an edit point on the second (target) curve where the curves will intersect.

This option has no effect when used in a perspective window.

View

Create the intersection where the curves cross in the view window.

• If the curves do not cross in the view, the Adjust intersection tool reports an error and does not modify the curves.

• If the curves cross more than once, the Adjust intersection tool will ask you to click near the intersection you want.

Closest

Move or deform the first (base) curve to intersect the second (target) curve at the nearest possible point.

That is, the base curve moves or is deformed the minimum distance necessary to intersect the target curve.

These options are available when the Modification Mode is Segment.

Segment Options

Segment Selection

Manual-asks you to pick the start and end edit point of the segment to be modified.

Entire Curve-modifies the entire curve proportionally. The curve is modified less the further from the intersection.

Auto- automatically picks the segment to be modified based on the other options.

Start /End Modification

Free-the start/end of the modified segment can move.

Fixed-the start/end of the modified segment stays fixed.

Fixed Tangent-the start/end of the modified segment stays fixed as well as its tangent.