The Projection Tool has three modes. In the first mode you can use a planar…
Vectorworks Tip #137 – 3D Modelling – Project Tool 2
The second mode of the Project Tool is similar to the first mode except that it cleans up the area where you have split the original NURBS surface. In other words the NURBS surface is trimmed to the shape of the planar object. This makes a very quick to create a NURBS surface and then trim it to the shape that you want.