Select the 
button from the Surface
toolbar or the B Spline (Surface menu)
command. The dialog box for the command is displayed.
Select the Laced check box if you want to digitise points in a laced pattern. See Creating Spline Surfaces for a diagram.
Type the degree of curvature in the U and V directions into the U Degree and V Degree boxes, respectively.
Type the number of digitised control points in the U and V directions into the U Points and V Points boxes, respectively.
Type a Name for the surface, if required.
Select Display to set the surface display parameters. The Display parameters now appear.
Enter the required number of patches in the U and V directions into the U Patch and V Patch boxes respectively.
Enter the required number of display points in the U and V directions into the U Display and V Display boxes respectively.
Click OK to accept the command parameters.
Digitise control points in response to the ‘Digitise control grid points (or return)’ prompt. The first row of points defines the U axis direction.
Perform a finish.