Ebook Tutorial AutoCAD

AutoCAD 2008 Tutorial
Second Level: 3D Modeling

As illustrated in the previous chapters, there are no surfaces in a wireframe model; it
consists only of points, lines, and curves that describe the edges of the object. Surface
modeling was developed to provide the surface information that is missing in wireframe
modeling. Essentially, defining the skin of a design creates a surface model. Although it
is possible to create a surface model without using a wireframe model, in most cases it is
much easier to create a surface model on top of a wireframe model. In surface modeling,
a wireframe model can be used to provide information about the edges and corners so
that the desired faces can be easily positioned and placed.

Surface modeling is more sophisticated than wireframe modeling in that surface modelers
define not only the edges of 3D objects, but also the surfaces. Surface modeling provides
hiding, shading, and rendering capabilities that are not available in wireframe modeling.
Surface models do not provide the physical properties that solid models provide, such as
mass, weight, center of gravity, and so on.

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. It is important to note that the AutoCAD surface
modeler does not create true curved surfaces. To differentiate these two types of surfaces,
faceted surfaces are called meshes in AutoCAD. Because of the use of faceted
approximation on true curved surfaces, the computer requirements of most faceted
surface modelers are typically much less than that of solid modelers. Faceted surface
modeling usually provides reasonably good representations of 3D designs with fast
rendering and shading capabilities. Faceted surface models are also useful for creating
geometry with unusual surface patterns, such as a 3D topographical model of
mountainous terrain.

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