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:

1. Create a set of NURBS curves.

Four cross section 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 XSect tool.

Activate the cross section tool

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.
 

A NURBS surface created through the selected curves
 
Tutorial project: 'tutorprojects\modeling\nurbs\cross_section\cross_sections'

Mixing curves of different order

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.

Four closed curves defining the cross sections of the tube

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 'Accept' the tool.

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.

A NURBS 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.

Cross section curves representing the left side of the 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.

 
Face curves seen from the top

3. Multi select the curves in the correct order and apply the XSect tool. Set the 'Order' option to 'Cubic' and click 'Accept'.

One half of a face defined by a number of vertical cross section curves
 

Tutorial project: 'tutorprojects\modeling\nurbs\cross_section\semi head'
 

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: 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 resulting surface contains both open and closed sections