CV surfaces are NURBS surfaces controlled by control vertices (CVs). The CVs don’t lie on the surface. They define a control lattice that encloses the surface. Each CV has a weight that you can adjust to change the shape of the surface.
Because an initial NURBS surface is meant to be edited, the surface creation parameters do not appear in the Modify command panel. In this respect, NURBS surface objects are different from other 3DS MAX objects. The Modify command panel provides other ways to change the values you set in the Create panel.
Note: When you edit a CV surface you can add or move CVs so that more than one CV is at the same location (or close to it). This increases the influence of the CVs in that region of the surface. Two coincident CVs sharpen the curvature. Three coincident CVs create an angular peak in the surface. This technique can help you shape the surface. However, if you later move the CVs individually, you lose this effect. (You can also obtain the influence of multiple CVs by fusing CVs.)
The creation parameters are the same for both Point Surfaces and CV Surfaces.
Length: The length of the surface, in current 3DS MAX units.
Width: The width of the surface, in current 3DS MAX units.
In the Modify command panel, the Length and Width spinners are no longer available. You can change the length or width of the surface by scaling the surface at the Surface sub-object level. Moving CV sub-objects also alters the length and width of the surface.
Length Points: The number of CVs along the length of the surface. In other words, the initial number of CV columns in the surface. Can range from 4 to 50.
Width CVs or Width Points: The number of CVs along the width of the surface. In other words, the initial number of CV rows in the surface. Can range from 4 to 50.
In the Modify command panel, the CV Length and Width spinners are no longer available. You can change the number of rows and columns by deleting existing rows and columns, or by adding new rows and columns using the Refine controls at the Surface CV sub-object level.
Generate Mapping Coordinates: Generates mapping coordinates so you can apply mapped materials to the surface.
The Generate Mapping Coordinates control is present in the Modify command panel. It is at the Surface sub-object level.
When you modify a CV surface, a rollout lets you change its surface approximation settings.
The Keyboard Entry rollout lets you create a CV surface by typing. Use the TAB key to move between the controls in this rollout. To press the Create button, use ENTER while the button is active.
X, Y, and Z: Enter the coordinates of the center of the surface.
Length and Width: Enter the dimensions of the surface, in current 3DS MAX units.
Length CVs: Enter the number of CVs along the length of the surface (this is the initial number of CV columns).
Width CVs: Enter the number of CVs along the width of the surface (this is the initial number of CV rows).
Create: Creates the surface object.