From Drawings . . . to Models - AutoCAD 2012 - page 517

play that style when it's opened in AutoCAD LT — however, there's no way of
changing it to 2D wireframe (or anything else) so you can actually work on it.
From Drawing to Modeling in 3D
This section introduces three techniques for creating 3D objects: drawing 3D lines and
polylines, creating 3D objects from 2D geometry, and creating solids. (In AutoCAD LT
you can use the first two techniques only.) AutoCAD is also very capable at surface mod-
eling, offering both freeform mesh and NURBS surfaces. If you're interested in either of
these, check out the online help system — navigate to User's Guide, then choose Work
with 3D Models, and then Create 3D models. Topics include creating surfaces and
meshes from scratch, and creating solids and surfaces from 2D objects.
When you draw 3D objects, just like when you draw 2D objects, put them on
appropriate layers and use precision techniques to specify each point and dis-
tance. (See Chapter 5 for more information.)
Drawing basic 3D objects
The most basic forms of 3D geometry are wireframe-like objects created by picking
points or entering X,Y,Z coordinates. Such objects have no surfaces, so look the same in
2D Wireframe mode or a photorealistic rendering. They are most useful as paths for
sweeps and lofts, or as edges for surface creation. Such objects include
Lines. Lines are really 2D objects; although you can specify different z-coordinates
for start- and endpoints so they are not coplanar with the world coordinate sys-
tem, each individual segment is based on its own 2D plane. You can, however, use
lines for constructing objects in 3D space.
3D Polylines. Created with the 3DPOLY command. Similar to the 2D polylines I de-
scribe in Chapter 8, except the vertices of 3D polylines can have different z-co-
ordinates (2D polylines must be planar). 3D polylines are useful as paths for
sweeps or for fly-throughs (I don't cover walk-throughs or fly-throughs in this
topic).
Splines. Splines are freeform curves, created with the SPLINE command and I de-
scribe them in a 2D context in Chapter 9. Splines are 3D objects and vertices can