## Cross Section Surfaces

The Cross Section tool constructs a surface, which passes through a given set of cross section curves. To create a cross section surface:

Four cross section curves
 1. Create a set of NURBS curves. 2. Multi select the curves in the order in which the surface should interpolate through the curves. The control bar now shows you NURBS specific construction tools. Click the X-Sect tool. Cross Section tool A NURBS surface created through the selected curves

You can now see two cross section tool specific options in the control bar: Closed and Order. We will create a cubic mesh through the curves. Therefore, set the Order to Cubic and click Accept to create a surface.

Tutorial project: 'tutorprojects\modeling\nurbs\cross_section\cross_sections'

The cross section tool can handle curves of any order. Some of the curves can be polygonal and some cubic, for example.

Let's create a tube, which starts with a round smooth shape and ends to a polygonal form.

 1. Create two closed cubic NURBS curves and two closed polygonal curves, as shown in the next picture. 2. Select the curves from left to right (in the order in which you want to connect them). Activate the XSect tool, set Order to Cubic and click Accept. Four closed curves defining the cross sections of the tube A tube created through four closed curves with different orders

### Creating a face from cross section curves

This tutorial demonstrates how to create a human face using the cross section tool.

1. Create a curve representing the profile of a face.

2. Duplicate the profile curve and modify it to get the next 'slice' of a face. Continue this way until you have the necessary cross section curves for one half of a face.

3. Now displace the curves by rotating them from the top view. You can also single point edit the curves from the front view to get non-planar curves.

 A NURBS curve representing the profile of a face Cross section curves for one side of the face Face curves seen from the top
 4. Multi select the curves in the correct order and apply the XSect tool. Set the Order option to Cubic and click Accept. Tutorial project: 'tutorprojects\modeling\nurbs\cross_section\semi head' One half of a face defined by a number of vertical cross section curves

### Editing construction curves

As usual, the original construction curves are placed inside the mesh and you can modify them in order to control the shape of the mesh.

If you delete one of the construction curves, the corresponding curve is also removed from the actual mesh. For example, to make the head we created in the previous example complete, duplicate and mirror the cross section curves and then drop the duplicates to the beginning of the construction history in inverted order (the order of the doubled curve set must be correct).

Note Note: If you need to delete the cross section curves but you don't want to delete the mesh, switch the Constructor of the mesh to None from the property window's Spec tab before deleting the curves.

### Mixing open and closed curves

 You can freely mix open and closed curves to define a cross section surface. For example, you can create a tube through three open and three closed curves, as demonstrated by the following image: Three open and three closed curves
The result surface contains both open and closed sections