2008

a solid object. In a cube, for example, there is seldom the need to view the
inside surface of any of the six squares that make up the cube. So for many
viewing and rendering operations, 3ds Max ignores a face if it's facing away
(that is, if its face normal is directed away) from a point of view.
When you create objects in AutoCAD, AutoCAD Architecture, or Revit, 3ds
Max generally understands which way faces should be oriented and manages
face normals accordingly. However, occasionally you may encounter linked
drawing geometry that displays correctly in AutoCAD, AutoCAD Architecture,
or Revit, but doesn't strictly respect face-normal conventions. This can make
it appear as though elements visible in the drawing file are missing or appear
“inside-out” in 3ds Max.
If this happens, try one of these four options:
■ During file link or import of the DWG file, turn on the Unify Normals
switch in either the Basic panel of the File Link Settings dialog or the
Geometry Options group of the AutoCAD DWG/DXF Import Options
dialog.
■ If the drawing is already linked or imported, assign a
Normal modifier on
page 1509 to the object that is not displaying properly. Turn on the Unify
Normals switch to force all the normals to face the same direction. If the
object then appears to be “inside-out,” turn on the Flip Normals switch as
well.
■ Turn on the Force 2-Sided switch on the Render Scene dialog (to render
the faces correctly), and turn on Force 2-Sided on the Viewport
Configuration dialog (to display the faces correctly in the viewports.)
■ Apply a material with the 2–Sided switch turned on.
NOTE Using the Force 2–Sided options can result in slower performance,
particularly when rendering. Using either of the Unify Normals options is the
preferred method of handling face normals.
If you are experiencing a high volume of face normal problems in a particular
file, you should verify that the Weld switch is turned on in the File Link
Settings dialog
on page 6793 , and then reload the drawing. Weld forces nearby
faces to share edges and vertices. This can still result in groups of face normals
that are flipped in 3ds Max so the Unify Normals switch should also be used.
NOTE The disadvantage of welding is that it can be time-consuming when you
attach and reload the linked file. The time penalty is much greater when 3ds Max
is creating objects that have very large numbers of individual faces.
6778 | Chapter 21 Managing Scenes and Projects