Drawing in 3D on a flat 2D screen is challenging. You can only draw in 2 dimensions at a time and even the humble 3D point has an X, Y, and Z position.

Construction Planes, or “CPlanes,” help solve this fundamental problem. CPlanes are infinite virtual planes that form the basis for creating geometry.

All Rhino views have their own CPlane. The Top view uses World XY plane. The Front view uses the World XZ plane and the Right view uses the World YZ plane. With a CPlanes, you can predefine that “unset” coordinate. Creating a point in Top view means it’s Z-coordiate stays 0. You can even create your own custom CPlanes.