The AutoCAD surface modeler defines faceted surfaces using a filled polygon. The created faces of surface models are only planar, which means the surface models can only have approximate curved surfaces. ...

AutoCAD 2007 provides three basic methods for creating surfaces â the 2D Solid, 3D Face and Region commands. The three commands were developed parallel to the historical development of the different types of computer modelers.

• 2D Solid: The first generation surface command available in AutoCAD. Used mostly to fill an area in the sketch plane of the current UCS. This type of surface is not a true 3D surface.
• 3D Face: Creates a true 3D planar surface (allowing X, Y and Z coordinates) of three-sided or four-sided shape. This is the type of surface developed primarily for creating faceted surface models.
• Region: Creates a 2D surface of arbitrary shape from existing 2D entities. This command creates the most flexible and the most complicated type of surface available in AutoCAD. This command was developed to allow manipulation of 2D surfaces using one of the solid modeling construction techniques, namely, the Constructive Solid Geometry method.

The first generation surface available in AutoCAD is used to fill an area in the sketch plane of the current UCS. It is therefore necessary to properly orient the UCS prior to using the 2D Solid command.

The second generation of surface command made available in AutoCAD was the 3D Face command. The 3D Face command can be used to create true 3D planar surfaces by allowing the X, Y and Z coordinates of the corners to be selected independently of the current UCS. The created polygon can be a three-sided or four-sided shape. This command is the primary construction tool for surface modeling in AutoCAD.


Source: www.acaddemo.com