Creating a Loft Surface

The Loft Surface tool creates complex NURBS surface(s) from two or more cross sections with no rail, with a rail and one or more cross sections, or with two rails and one cross section. A rail is a guide curve which determines the shape of the resulting surfaces, in the one rail mode. In Birail Sweep mode, the rails do not need to intersect the cross sections.

Three modes are available.

 

Mode	Description
Loft With No Rail	Creates a NURBS surface using two or more cross sections
Loft With One Rail	Creates a NURBS surface using a rail and one or more cross sections
Birail Sweep	Creates a NURBS surface using two rails and one cross section

Similar to the Multiple Extrude command, the Loft Surface tool creates a 3D object from a series of other objects. Unlike Multiple Extrude, the cross sections do not need to be equally spaced, and the resulting profile can be manipulated to avoid self-intersection and to control twist.

This tool can potentially create surfaces which cannot be further manipulated in the 3D Power Pack. See Surface Geometry Requirements.

Loft Surface Using No Rails

 

To create a NURBS surface from two or more cross sections:

1.	Click the Loft Surface tool from the 3D Modeling tool set, and then select Loft With No Rail from the Tool bar.

2.	Click on each cross section. The cursor changes into an arrowhead when over a valid cross section. The point nearest to the click is selected.

The proposed curve alignment displays in red as each section is selected.

Cross sections are created using NURBS curves which do not need to be the same shape or planar. All NURBS curves must be either closed or open objects, not a mixture of the two. 3D loci can be used in a loft, but must display at the ends of the loft.

3.	Once all curves are selected, press Enter (Windows) or Return (Macintosh) or click the check mark button on the Tool bar.

The Loft Creation dialog box opens.

4.	Specify the desired loft creation settings.

 

Parameter	Description
Select Curve	Selects the previous or next cross section curve. Reverse changes the direction of the curve to twist or untwist the loft surface.
Reverse	Click to reverse the curve direction
Select Alignment by Point	Selects the previous or next point on the selected cross-section curve. If the cross section does not have any corners, this option is disabled.
Select Alignment by Percentage	Selects points along a geometrically-continuous cross section (such as a circle) by a specified percentage, or by adjusting the slider
Ruled	Creates a linearly-interpolated object
Closed	Creates a loft surface that closes in on itself. Because the start point cannot be selected as the end point of a loft, the Closed option automatically completes the connection.
Create Solid	Creates a solid loft surface with capped ends
Keep Curves	Retains the cross sections after the loft is created
Preview	Displays the proposed loft surfaces based on the current settings

5.	Click OK to close the dialog box and create the loft surface(s).

Loft Surface Using One Rail

 

To create a NURBS surface using one rail:

1.	Click the Loft Surface tool from the 3D Modeling tool set, and then select Loft With One Rail from the Tool bar.

2.	Click on the rail, and then click on each cross section.

3.	Once all curves are selected, press Enter (Windows) or Return (Macintosh) or click the check mark button on the Tool bar.

The Loft Creation dialog box opens.

4.	Specify the desired loft creation settings (see Loft Surface Using No Rails).

5.	Click OK to close the dialog box and create the loft surface(s).

The rail curve should intersect all cross-section curves if there is more than one curve.

When a single cross section is used, the curve is swept along the rail and the cross section does not need to intersect the rail.

Loft Surface Using Two Rails

 

To create a NURBS surface using two rails:

1.	Click the Loft Surface tool from the 3D Modeling tool set, and then select Birail Sweep from the Tool bar.

2.	Click on each rail, and then click on the cross section. The cross-section profile curve does not need to intersect the rail curves.

In this mode, only one cross section can be selected.

3.	Once the profile curve is selected, press Enter (Windows) or Return (Macintosh) or click the check mark button on the Tool bar.

The Loft Creation dialog box opens.

4.	Specify the desired loft creation settings (see Loft Surface Using No Rails).

5.	Click OK to close the dialog box and create the loft surface(s).

The loft surface is created differently depending on whether the profile curve is open or closed, and how the start/end of the rails touch the profile curve. In certain instances, the click order (which rail is clicked first) and location (part of the profile curve that is clicked) will produce a different loft surface.

 

Status of Profile Curve and Rails	Effect of Rail Click Order/Profile Click Location
Open Profile Curve
Start/end of one of the rails touches the start/end of the open profile	The rail click order and profile click location do not affect the loft surface creation
Start/end of the rails do not touch the start/end of the open profile, or do not touch the open profile at all	Both the rail click order and the location where the profile is clicked affect how the loft surface is created
Closed Profile Curve
Start/end of one of the rails touches the closed profile curve	The click order and location do not affect the loft surface creation
Start/end of the rails do not touch the closed profile at all	The click order affects how the loft surface is created