Depict the methods of deriving curves from existing curves.

What will be an ideal response?

To ease the task of sketching or interpolating on a surface or polygon mesh, you can first construct a planar curve and then project or pull it onto a surface or a polygon mesh to obtain a curve on the surface or the polygon mesh. If edges and borders of a surface or polygon mesh are required for the development of some other geometric objects, you extract them. Curves and points produced from the intersection of two surfaces/two polygon meshes and intersection of a surface/polygon mesh and a curve are sometimes required for further design work. From an existing surface, you can construct contour curves, section curves, and silhouettes, and can extract isocurves, control points, and isocurve wireframe. You can also extract a portion of a curve.