3D represents a major breakthrough for Computer Aided Design applications like AutoCAD. Aside from seeing a realistic representation of the designed object, understandable even for those unfamiliar with the technical drawing conventions, it offers the advantage that, instead of drawing each projection separately, we can now generate all the views automatically from the three-dimensional model. We can even take advantage of new techniques of stereolithography, generating and sending through the new _3DPRINT command a STL file created from our 3D model to a specialized company that will return in a few days the plastic model of our design.

It is with AutoCAD 2012 that we finally have complete implementations of the three classical paradigms for modeling three-dimensional objects:

- Constructive Solid Geometry (CSG).
- Procedural or NURBS Surfaces.
- Subdivision surfaces.

AutoCAD solves the dilemma about which three-dimensional object modeling method to use -solids, surfaces or meshes- in a very practical way, allowing us to freely combine the three of them. Meshes, Surfaces and Solids can be converted into each other. Solids can be sliced using Surfaces; a portion of space completely bounded by Surfaces can become a Solid; Surfaces can be thickened so that they become Solids. This makes AutoCAD today a perfectly valid application for the creation and management of 3D objects. And compels us to explore in a book like this, dedicated to Visual LISP programming, its ability to operate in this environment.

These subjects are developed in the following Chapters:

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