Lofting a NURBS surface
Creating a UV Loft surface
Lathing a NURBS surface
Creating a 1-rail and 2-rail sweep surface
Sculpting a rectangular NURBS surface
You learn many details of working with NURBS as you dive in and start building NURBS objects. This bonus chapter includes several tutorials that can help as you try to grasp the power and flexibility of modeling with NURBS.
U Loft is one of the most versatile NURBS surface tools: You can use it to create simple or very complex surfaces. In the following tutorial, you create a spoon by lofting a NURBS surface over a series of point curve cross sections using the U Loft tool. This tool requires sections in the horizontal (U) direction.
Lofting a skin over a series of cross-section curves can create NURBS surfaces. In this tutorial, you create the point curves necessary for modeling a NURBS spoon. Then you use the U Loft tool to skin the surface and create the finished spoon.
To create a NURBS spoon using the U Loft feature, follow these steps:
This file includes 10 cross-section NURBS point curves that are correctly positioned to form a spoon.
The cursor changes to a pointer accompanied by the U Loft Surface icon. (Notice that when you place the cursor over a cross section, it changes to a cross and the curve turns blue.)
Note
You also can create this surface using the U Loft button found in the Create Surfaces rollout.
The first section of the lofted NURBS surface is then generated as indicated by the green isoparm lines displayed in the viewport.
Figure 1 shows the completed NURBS spoon.
A UV Loft surface can have more complex contours than a U Loft surface. UV Lofts are created from several curves spanning two dimensions; the U dimension is horizontal, and the V dimension is vertical. To use this tool, select the cross-section curves in the order that they will be skinned along the U dimension, right-click in the viewport, and click the cross-sectional curves for the V dimension. The resulting surface is made up of cross-sectional curves for both dimensions to create a complex NURBS surface. Just like the U Loft surface, all curves need to be attached to the same NURBS object.
As an example, Figure 2 shows a chair seat that has been created with the UV Loft tool using three curves in the U direction and five curves in the V direction, thus enabling the surface to be contoured to fit a human being without you having to go back later and modify it by moving control vertices.
This technique is very useful for building mechanical shapes, automobiles, and spaceships, and for modeling product designs.
Lathing a NURBS curve works the same way as lathing a spline. You simply need to select a curve, click the Lathe button in the Create Surface rollout (or click the Create Lathe Surface button in the NURBS Creation Toolbox), and then click the curve. You can change the Degrees value and the axis of rotation in the Lathe Surface rollout that appears under the Create Surfaces rollout in the Modify panel.
In this tutorial, you create a NURBS CV curve profile shape. You then use this curve with the Lathe modifier to create a vase.
To create a Lathed NURBS surface, follow these steps:
This file includes two CV curves that you can lathe to create a vase.
Figure 3 shows the completed vase produced using the Lathe tool.
The 1-rail sweep surface tool lets you create a NURBS surface by using one NURBS curve to act as a side rail and one or more profile shape curves to sweep along the rail to generate the surface. A 2-rail sweep surface is similar, except that it uses two NURBS curves as side rails.
Now that you have carefully constructed a flower vase, you need to create some flowers to place in the vase. You start with the flower stem.
To create a NURBS point surface using a 1-rail sweep, follow these steps:
This file includes three cross sections and a curve correctly positioned that you can sweep to form a flower stem.
The NURBS skin is generated on the stem, as shown in Figure 4.
NURBS patches are a quick way to create a surface that can be sculpted using the subobject elements, such as a control lattice. For each subobject type, you can use many different tools to form the patch.
In this tutorial, you create a NURBS CV surface plane sculpted into a leaf for the NURBS flower. To do this, you work in the Surface CV subobject level and use the Select and Move transform tool to move CVs and sculpt the NURBS rectangle into a leaf shape.
To create a rectangular NURBS CV surface, follow these steps:
The CV lattice is displayed in the Top viewport.
This step gently rounds the outside contours of the NURBS surface.
The leaf should now be U-shaped.
Figure 5 shows the NURBS leaf with the control lattice visible.
Continuing to build your flower, you now sculpt a second rectangular NURBS surface into the shape of a flower petal. In this case, the center CVs of the surface are raised to create a soft, rounded shape. You sculpt one end of the NURBS rectangle into a blossom petal shape and then scale and clone it to create three more petals.
To sculpt the flower petal shape, follow these steps:
This step rounds the outside corners of the petal.
Figure 6 shows the completed flower.
To finish the flower and vase model, you need to merge all the parts of the flower vase project into one scene. Clone and position the leaves next to the stem. Position the stem in the throat of the vase at a slight angle. Position the leaves midway up the stem and then place the flower at the top of the stem, at right angles to the leaves. Finally, apply texture maps to all objects, using a glass material for the vase, dark green for the leaves and stem, and a yellow radial gradient for each petal of the blossom. The finished flower is shown in Figure 7.
The Modifiers NURBS Editing menu includes a set of modifiers unique to NURBS objects. This set includes the following modifiers: Surface Select, Surf Deform, and Disp Approx.
The NURBS Surface Select modifier (known in the Modifier List as NSurfSel) lets you make a subobject selection for the selected NURBS object. This selection is then passed up the Modifier Stack to the next modifier. The two subobjects for this modifier are Surface CV and Surface.
The Surf Deform modifier works on NURBS surfaces just like the PatchDeform and PathDeform modifiers. After applying this modifier, you can select another NURBS object with the Pick Object button to deform the selected NURBS object. This modifier also has a World-Space version.
The Displacement Approximation (or Disp Approx) modifier makes displacement mapping (which is applied using materials) available in the Modifier Stack. This modifier alters the surface of an object based on displacement mapping. This modifier can work with any object that can be converted to an Editable Mesh, including primitives, NURBS, and Patches. Parameters for this modifier include Subdivision Preset settings of Low, Medium, and High.
The Displace NURBS World-Space modifier is similar to the Disp Approx modifier. It can convert a NURBS object into a mesh object and includes the effect of a displacement map. In the Displace NURBS rollout, you can select the Tessellation method to be Regular, Parametric, Curvature, or Spatial; or both Spatial and Curvature.
Note
Because U and V curves implicitly define a NURBS object's surface, they don't require mapping modifiers.
NURBS are an ideal method for modeling if you require free-flowing models. This chapter covered the following topics:
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