Under Edit there are six items. They are Undo Last Operation, Redo Last Operation, Create Surface, Edit Control Point, Convert Surface to, and Delete Current Surface. Of these six, only Edit Control Point and Convert Surface to have sub-items.

  1. Create creates a surface of the type selected previously using Surface, followed by Surface Type, followed by one of the four supported surface. In general, to create a surface, you should first select a surface type and then select Create.

    If the surface type is B-spline and NURBS, a Set Surface Parameters appears:

    Click the number of rows, the number of columns, the degree in the u-direction and the degree in the v-direction. Then, click OK. A flat surface of the selected type will appear on the drawing canvas.

    If the selected surface is a Bézier or a rational Bézier surface, the Set Surface Parameters window only has two lines, the number of rows and the number of columns, because the degrees are determined by the row number and column number.

  2. Delete Current Surface removes the current surface from the scene.

  3. Edit Control Point has three sub-items:

  4. Convert Surface to has four sub-items: When converting a surface type to another, those unnecessary information will be ignored. For example, if a NURBS surface is converted to a B-spline surface, all weights are set to 1; if a B-spline surface is converted to a Bézier surface, the degrees and knot vectors are ignored since the number of rows and columns of control points determine the degrees of the resulting Bézier surface. As a result, the shape of a surface will change after the conversion.

  5. Undo Last Operation and Redo Last Operation are complement operations. Please note that geometric transformations cannot be undone and redone. Only those operations listed in Advanced Features can. Undo Last Operation will undo the last performed operation (e.g., knot insertion), while Redo Last Operation will redo the last undone operation. For example, if a surface subdivision is performed, followed by an undo, followed by a knot insertion. Then, a redo will redo the surface subdivision.