Surfaces Vs. Solids

When you extrude, sweep, loft, and revolve curves, you can create both solids and surfaces. Open curves always create surfaces, but closed curves can create either solids or surfaces depending on the situation.

If you select a closed curve and click EXTRUDE, SWEEP, LOFT, and REVOLVE on the ribbon, you create:

• A solid if the Solid tab is active.
• A procedural surface if the Surface tab is active.
• A NURBS surface if the Surface tab is active and the SURFACEMODELINGMODE system variable is set to NURBS.
• An associative surface if the Surface tab is active and if surface associativity is on.

In this illustration, the same profile creates a solid (left), a procedural surface (middle), and a NURBS surface (right).

To create a surface when the Solid tab is active or a solid when the Surface tab is active, select the Mode option and select surface while you are creating the object.

Geometry That Can Be Used As Profiles and Guide Curves

The curves that you use as profile and guide curves when you extrude, sweep, loft, and revolve can be:

• Open or closed
• Planar or non-planar
• Solid and surface edge subobjects
• A single object (to extrude multiple lines, convert them to a single object with the JOIN command)
• A single region (to extrude multiple regions, convert them to a single object with the REGION command)

Create Associative Surfaces

Surfaces can be associative while solids cannot. If surface associativity is on when a surface is created, it maintains a relationship with the curve from which it is was generated (even if the curve is the subobject of another solid or surface). If the curve is reshaped, the surface profile automatically updates. See Create Associative Surfaces.