A U loft surface interpolates a surface across multiple curve sub-objects. The curves become U-axis contours of the surface.
Using multiple curves to create a U Loft surface
Closed U lofts
When you create a U loft, you can select curves that are not already sub-objects of the active NURBS model. You can select another curve or spline object in the scene. When you select that curve, it is automatically attached to the current object as if you had used the Attach button.
As you move the mouse over a curve that is not part of the active NURBS object, the cursor changes shape to indicate you can pick the curve, but the curve is not highlighted in blue.
The NURBS object must contain at least two curves.
(Create U Loft Surface).
The U loft is created. It is "stretched" across the curves you click. The order in which you click the curves can affect the shape of the U loft surface. The names of the curves appear in the U Loft Surface creation rollout.
While creating a U loft, you can press Backspace to remove the last curve you clicked from the list of U loft curves.
The Flip Normals control lets you flip the surface normals at creation time. (After creation, you can flip normals using controls on the Surface Common rollout.)
To create a U loft with automatic attach (example):
Create panel and create three or more independent CV or Point NURBS curves.
Modify panel. In the NURBS toolbox, click to turn on (Create U Loft Surface).
3ds Max creates the U loft. You don't have to collapse the curves to a NURBS surface, or attach them to an existing NURBS model.
As you move the mouse over a curve that is not part of the active NURBS object, the cursor changes shape to indicate you can pick the curve, but the curve is not highlighted in blue.
While a U loft sub-object is selected, a rollout with the U loft parameters is displayed at the bottom of the Modify panel. This rollout appears only when one U loft sub-object is selected. It isn't possible to edit more than one U loft at a time, so unlike some other NURBS sub-objects, the rollout doesn’t appear when multiple U loft sub-objects are selected.
When you create lofted and swept surfaces, you have access to all the parameters, and some of the editing operations, of the surface. You can reverse and set start points on curves while you create the surface. You can also use the arrow buttons to change the order of the curves, and you can remove a curve with the Remove button.
U Loft Surface rollout (creation time)
This list shows the name of the curves you click in the order you click them. You can select curves by clicking their names. Viewports display the selected curve in blue. Initially the first curve is the one selected.
You can also select more than one curve at a time. This is useful when you use the Edit Curves button.
These controls affect individual curves you select in the U Curves list, as opposed to properties of the loft surface in general. They are enabled only when you have selected a curve in the U Curves list.
Adjusts the position of the curve's start point.
This control is disabled if the curve is not a closed curve.
While you're adjusting start points, a dotted blue line is displayed between them, to show the alignment. The surface is not displayed, so it doesn't slow down adjustment. When you release the mouse button, the surface reappears.
U Loft Surface rollout (modification time)
This list shows the name of the curves you click, in the order you click them. You can select curves by clicking their names in this list. Viewports display the selected curve in blue. Initially the first curve is the one selected.
You can also select more than one curve at a time. This is useful when you use the Edit Curves button.
These controls affect individual curves you select in the U Curves list, as opposed to properties of the loft surface in general. They are enabled only when you have selected a curve in the U Curves list.
Adjusts the position of the curve's start point.
This control is disabled if the curve is not a closed curve.
While you're adjusting start points, a dotted blue line is displayed between them, to show the alignment. The surface is not displayed, so it doesn't slow down adjustment. When you release the mouse button, the surface reappears.
Refines the U loft surface. Click to turn on Refine, then click a U-axis iso curve on the surface. (As you drag the mouse over the surface, the available curves are highlighted.) The curve you click is converted to a CV curve and inserted into the loft and the U Curves list. As when you refine a point curve, refining a U loft can change the curvature of the surface slightly. Once you've refined the surface by adding a U curve, you can use Edit Curve to change the curve.
Lets you edit the currently selected curve without switching to another sub-object level. Click to turn on Edit Curve. The points or CVs of the curve are displayed, as well as the control lattice if the curve is a CV curve. You can now transform or otherwise change the points or CVs as if you were at the Point or Curve CV sub-object level. To finish editing the curve, click to turn off Edit Curve.
When you turn on Edit Curves, all applicable rollouts for the selected curves are displayed, including the Curve Common rollout, the CV or Point rollout (depending on the curve type), and the CV Curve or Point Curve rollout. These rollouts appear beneath the U Loft rollout. They let you edit the loft curves and their points or CVs without having to switch sub-object levels.
