Merge Surfaces

The Draw->Merge Surfaces command in the Model module allows you to join two patch or NURBS surfaces to create a new (merged) surface.

Note:

Contrast this with Draw->Zip Surfaces, which joins points on one surface to points on another. Zip Surfaces does not create a new object. Instead, the support surface is unchanged, but the points of the zip surface are joined to points on the support surface.

Surfaces may be merged or blended, depending on the options you select. Certain options preserve the shape of the original surfaces 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 existing surfaces to merge them.

For purposes of simplification, the general term combining is used in the following description.

Notes

• You can only combine surfaces along open edges.
• You cannot combine patch and NURBS surfaces.
• The curves of both surfaces to combine must be of the same degree in u and in v. For example, you can combine two NURBS which are both cubic in u and linear in v, or you can combine two patches which are both Cardinal in u and B-Spline in v.
• Patch surfaces must have the same number of control points in the direction of the merge.
• NURBS surfaces can be combined with a different number of control points.
• SOFTIMAGE 3D allows you to import NURBS curves of a degree greater than 3 (cubic). These curves of higher degree may not have all the options available.
• Linear and Bezier type surfaces are combined immediately. NURBS, Cardinal, and B-Spline surfaces require that you fill in the relevant dialogue box. In the case of NURBS, the dialogue box is interactive.

Procedure

1. Position the surfaces as desired, so that open edges are appropriately positioned.
2. Choose the Draw->Merge Surfaces command.
3. Pick an edge of the first surface. The edge is highlighted.
4. Pick an edge of the second surface.
5. Set the parameters as desired. In the case of NURBS, the dialogue box is interactive.
6. Click Ok to accept the settings or Cancel to exit the dialogue box.

The original surfaces remain as they are, and a set of combined surfaces is created.

Patches

If the surfaces are Cardinal or BSpline in the direction of the combination, the Merge Patches dialogue box is displayed.

Last & First Row

The last row of points on the first surface and the first row of points on the second surface are not part of the combination. This provides additional control over the resulting surface.

Tip:

You can achieve the same result by deleting the last and first rows using the Edit->Delete Point command, then setting the Number of rows option to 0.

Number of Rows

The number of rows to use in the combination. The range is from 0 to the number of rows in the smaller surface.

Row Interpolation Factor

The row interpolation factor range is from 0 to 1. This allows you to define how the rows interpolate when creating the new surface.

• 0: The first surface does not deform.
• 1: The second surface does not deform.

NURBS Merge/Blend

When combining NURBS surfaces, the following dialogue box is displayed.

This dialogue box is interactive so you can see the changes as you adjust the values.

Note:

SOFTIMAGE 3D allows you to import NURBS curves of a degree greater than 3 (cubic). These curves of higher degree may not have all the merge/blend options available.

Parameters

Blend Type

• Add linear (CO) segment combines the two NURBS surfaces with a zero degree continuity (positional only) to make a straight blend region between the ending and starting rows.
• Add smooth (C1) segment combines the two NURBS surfaces with first degree continuity (positional and tangential) to add a curved blend region between the ending and starting rows.
• Add smoother (C2) segment combines the two surfaces with second degree continuity (positional, tangential, and curvature) to make a smoother blend region between the ending and starting rows.
• Factor merges the last row of the first surface and the first row of the second surface into a single row which is also smooth and of second degree continuity (C2); its position is an interpolation of the two original rows. To subsequently adjust the placement of the new row, use the Blend Extent slider.
• Join second to first moves the second surface so that its first row is attached to the end row of the first surface.

Blend Parameters

These three sliders are not accessible unless you have selected (C0) or Join second to first as the Blend Type. By moving each one, you modify the shape of the blend region between the two original surfaces.

• Start Extent stretches the blend region along the side of the first surface.
• If you select Factor as Blend Type, the Blend Extent slider adjusts the position of the interpolated row used to create the blend region between the two surfaces.
  
  At 0, you preserve the position of the last row of the first surface and hence its overall shape. At 1.0, you preserve the position of the first row of the second surface and hence its overall shape. The default value of 0.5 is halfway between the two.
• End Extent stretches the blend region along the side of the second surface.

Last updated 08-apr-1998