Extrusion is the process by which a 2D enity is converted into a solid shape. Extrusion adds an extra dimension to 2D entities. Think of this as moving the entities through space, leaving a 3D trail behind them.
· Solid Extrusion lets you extrude vertically, creating a solid entity. The appearance of a Solid Extrusion is governed by the current Perspectives Settings 
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· Wireframe Extrusion lets you extrude in any direction. It is used for making Perspectives Pro symbols.
· You can extrude shapes that you have drawn straight onto a Perspectives grid. Alternatively, you can extrude shapes created using 3D Projection.
· Any closed shape can be extruded whether a single entity like a polygon, or any enclosed chain of entities.