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The Draw->Merge Curves command in the Model module allows you to combine any two open curves to make a new curve. When you choose this command, a different dialogue box is displayed according to whether you are joining Linear, Bezier, B-Spline, Cardinal, or NURBS curves.
Using these dialogue boxes, curves may be merged or blended, depending on the options you select.
Certain options preserve the shape of the original curves and add a new region between them. This operation is known as blending and the new region is called the blend region. Other options change the shape of the existing curves; this operations is known as merging.
For purposes of simplification, the general term combining is used in the following description.
For All Curve Types
- When you combine two curves, the original curves are preserved until you delete them. If you make a mistake in combining, delete the resulting curve and start again using the originals.
- The order of selection is significant; that is, the end of the first selected curve is joined to the start of the second selected curve. To help you see the starting point of curves, choose the Show->Edge Flags command. You can use the Effect->Inverse command to change the start and end points if necessary.
NURBS Curves
- You can only combine a NURBS curve with another NURBS curve, and the resulting curve is also a NURBS.
- Both curves must be of the same degree. For example, you can combine two NURBS curves of cubic degree, but not a quadratic and a cubic degree curve.
Note:
SOFTIMAGE 3D allows you to import NURBS curves of a degree greater than 3 (cubic). These curves of a higher degree may not have all the merge/blend options available.
- The blend region cannot be of a continuity higher than that of the curves you are merging. For example, if the curves are quadratic (C1), the blend region can be C0 or C1, but not C2.
Linear, Bezier, Cardinal, and B-Spline Curves
- You can combine different types of curves, but the resulting curve is Bezier. For example, you can combine a Cardinal and a B-Spline, but the result is a Bezier.
- When using the Factor option, the original curves must be of the same type.
- Select the first curve.
- Choose the Draw->Merge Curves command.
- For non-NURBS curves, the Merge Splines dialogue box is displayed, in which you select the desired parameters. Then pick the second curve.
- For NURBS curves, pick the second curve. The NURBS Merge/Blend dialogue box is displayed in which you select the desired parameters.
The two curves are combined.
Merge Splines
When combining Linear, Bezier, Cardinal, or B-Spline curves, a dialogue box is displayed.
Add Linear (CO) Segment between Them
Joins the end of the first and start of the second with a straight line.
Add Smooth (C1) Segment between Them
Joins the end of the first and start of the second with a smooth curved line.
Translate Second One to Join Extremity
Moves the second curve so that the its first point is attached to the ending point of the first curve.
Factor
Relevant only for Cardinal and B-Splines.
Factor creates the same type of curve as the curves used, so both curves must be the same type.
When you click Factor, you combine points from the separate curves and choose the position of the new (merged) points as follows:
The last three points of one curve and the first three of another are matched in three sets of 2. Each set is merged into one point, whose position is an interpolation between the two. The result is three points instead of six.
You can also adjust the position of these (merged) points by moving the slider between 0 and 1. By leaving the default value at 0, you preserve the position of the three last points of the first curve. At 1.0, you preserve the position of the first three points of the second curve (0.5 is halfway between the two).
NURBS Merge/Blend
If you are combining NURBS curves, the following dialogue box is displayed. The NURBS dialogue box is interactive, so your settings are applied immediately to the combined curves and can be viewed in the windows.
Note:
SOFTIMAGE 3D allows you to import NURBS curves of a degree greater than three (cubic). These curves of higher degree may not have all the options available.
Blend Type
The blend region cannot be of a continuity higher than that of the curves you are merging. For example, if the curves are quadratic (C1), you can specify C0 or C1, but not C2.
- Add linear (CO) segment combines the two NURBS curves with a zero degree continuity (positional only) to make a straight blend region between the curves. This is a linear degree
- Add smooth (C1) segment combines the two NURBS curves with first degree continuity (positional and tangential) to add a curved blend region between the curves.
- Add smoother (C2) segment combines the two curves with second degree continuity (positional, tangential, and curvature) to make a smoother blend region between the points.
- Factor merges the end points (last point of the first curve and the first point of the second curve) into a single point with second degree continuity (C2); its position is an interpolation of the two original points. To subsequently adjust the point position, use the Blend Extent slider.
- Join second to first moves the second curve so that its first point is attached to the end point of the first curve.
Blend Parameters
Note:
You cannot access all three sliders unless you select
Add C2 smoother segment or Factor as the Blend Type.
- Start Extent stretches the blend region along the side of the first curve.
- Blend Extent: If you select Factor as Blend Type, Blend Extent adjusts the position of the interpolated point used to create the blend region between the two curves.
- End Extent: Stretches the blend region along the side of the second curve.
Last updated 08-apr-1998