Chapter 17. Solid Modeling

Solid Modeling refers to a series of procedures for creating computer models of three-dimensional solids. Unlike other modeling paradigms, is characterized by the completeness of the information provided by the model, such as distinguishing between the model’s interior and the exterior space and  the possibility of querying its physical properties. The use of solid modeling techniques allows automating engineering calculations. The simulation, planning and verification of processes such as machining and assembly was one of the main reasons behind its development.
AutoCAD’s solid modeling functionality is limited. Autodesk markets Inventor, an application specifically oriented to mechanical design with all the solid modeling functionality required in these cases. 3DSolids and Surfaces are created and managed by an external modeling kernel. Up to AutoCAD 2002, the ACIS modeling engine developed by Spatial (www.spatial.com) was used. Since Release 2004, Autodesk’s own ShapeManager modeling technology derived from the ACIS geometric modeling kernel, is used for solid modeling in AutoCAD. The ShapeManager API is so far only available in ObjectARX, although the ActiveX methods exposed in previous releases and can be used from Visual LISP.
Release 2007 made it possible to modify the original components from which a complex 3DSolid form that was generated applying Boolean operations (union, subtraction and intersection) is composed. This capability is available for 3DSolids created through the user interface when the SOLIDHIST system variable is set. But for 3DSolids created by programming, its History property must be explicitly enabled. With this in mind, the sample programs included in this chapter will check the value assigned to SOLIDHIST so in case it is 1 the object’s History property will be set to Record (:vlax-true).

A complex 3DSolid is usually made up from the combination of a series of basic forms, known as primitives. Solid primitives cannot be created by entmake. Visual LISP allows their creation using  commands or through their equivalent ActiveX methods. Using ActiveX methods we can create rectangular prisms, cones, cylinders, elliptical cones and cylinders, spheres, tori and wedges.
In this chapter we demonstrate the use of ActiveX methods that create 3DSolids as primitives and from 2D objects using extrusion, sweep or revolution operations. We have also considered  the available commands that can be used through the command/vl-cmdf interface.

This Chapter includes the following sections:

17.1. 3DSolid Primitives.
17.2. Creating a Primitive using ActiveX.
17.3. Creating 3DSolids from 2D or 3D objects.
17.4. Creating Regions.
17.5. Sample Program: Complex Regions.
17.6. Properties and Methods of the 3DSolid object.
17.7. Sample Program: Extruded Solid.
17.8. Sample Program: Solid by Sweeping along a path.
17.9. Sample Program: Sweeping along a Helix.
17.10. AddRevolvedSolid: Solids of Revolution.
17.11. Sample Program: Creating a Solid  of Revolution.
17.12. Physical and Geometric Properties.
17.13. Summary.
Your questions or comments about this Chapter's contents are welcome!

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