As shown in Figure 1, control lines are spaced apart from one another. They can be open or closed, but you cannot have a mix of opened and closed control lines. form•Z refers to the direction along the control lines as the mesh's length, and to the direction across the control lines as its depth. It may help you to consider the C-Mesh tool as performing a sweep operation, with the control lines being the sweep objects and implied sweep paths being drawn by form•Z between matching points on the control lines. The tool is very flexible; it can adjust for differences in the number of points in the control lines, accommodate differences in directions of control lines, and control the curvature along the sweep paths (the depth curves).

Even though you can have any number of control lines, the C-Mesh tool itself will prompt you to select only two. Therefore, when you have more than two control lines (and you generally will) you must use the Pick tool to pre-select them, in their order, before you initiate the C-Mesh tool. Then, after setting the parameters of the mesh in the Tool Options palette, click anywhere in the drawing window to create the mesh.

The C-Mesh tool options are extensive, and, on some computers, some of its contents may not be visible. If this is the case, you can hold down the pick button of your pointing device to scroll through the palette's contents. You can also right-click the C-Mesh button to display the tool's options in dialog boxes. When your control lines are arranged in a circular pattern, as shown in Figure 1, select the Ring option to have the first control line connected to the last control line. The Round Front and Round Back options cause the mesh to curve inward at the specified ends. The extent of closure is controlled by the value in the Rounding Ratio Percentage edit box; with a value of 100 completely enclosing the end.

When you select Edit from the Tool Options palette, an edit mode version of the mesh is generated. In this edit mode the control- and depth-line segments are shown as heavy, dark lines along with the resulting mesh surface. You can move and twist the points on the segments as well as the segments themselves to change the shape of the mesh. When Adjust to New Parameters is selected, you can also change the curve type, the mesh density, and other parameters of an existing C-Mesh object.

Nurbz
form•Z's Nurbz tool creates surfaces that are based on NURBS (Non-Uniform Rational B-Spline) mathematics. Unlike C-mesh surfaces, nurbz surfaces are not faceted; they are always perfectly smooth. The Nurbz tool has two options for creating surfaces from wire objects--By Lofting and By Boundary Curves.

Select By Lofting to create a nurbz surface from a set of control lines. The action is similar to the C-mesh tool, and, like the C-mesh tool, the Nurbz tool uses the word length to indicate the direction along the control lines and the word depth to indicate the direction across the control lines. When you select this option, set the Depth Degree to a value one less than the number of control lines you intend to use. Usually you will use vector lines as control lines, and they become NURBS curves as the surface is created. The Length Degree option determines how close the curves conform to the original vector lines. When you set Length Degree to 1, the vector lines are unchanged; as you increase its value, the curvature of the vector lines become flatter. The Closed In Depth option creates a surface between the first and last control lines, similar to the Ring option of the C-mesh tool.

Figure 2. The Boundary Curve option of form•Z's Nurbz tool creates a surface from two, three, or four wireframe curves, as shown in these two examples. Use the Edit Controls tool to display and move the individual control points of a surface, as shown in the upper right.