Normals and Surface Orientation
Geometric surface normals
Surface normals are perpendicular directions that can point to one side of the surface or the other.
The direction of geometric normals is determined by the direction of the U and V hulls on a surface, according to the right-hand rule.
Normal directions are created automatically by the software as you create the surface, and it is common not to pay attention to them while modeling in Alias.
Geometric surface normals can be important when exporting models to other software that needs to interpret the inside/outside of the surfaces for visualization or solid modeling. The Shell Stitch tool is often used to ensure all geometric normals are unified.
Flipping geometric surface normals (red normals)
Geometric normal are also known as 'red normals' because of the color used to display and change them using the Set Geometric Surface Orientation tool. The direction of geometric normal is shown on the Point of Interest manipulator when viewing using the Shift and Alt keys, with either a blue or yellow to indicate the direction normal.
Changing the direction of the geometric surface normal changes the U or V directions and therefore delete the construction history of a surface.
Flipping visual surface orientation (yellow normals)
Visual surface orientation is also known as yellow normals because of the color used to display and change it using the Set Visual Surface Orientation tool.
The visual orientation of a surface is distinct from the U and V and geometric normal directions. Changing the visual orientation of a surface preserves construction history and does not affect texture mappings.
All tools, such as Ambient Occlusion, Draft Evaluation, Parting Line, and Offset, use orientation rather than surface normal to determine which way the surface is facing. When exporting a file, the surface orientation information is translated assuming the file format can support it in some way.
Tools
Tools that display or utilize the geometric normal direction:
Tools that modify geometric normals:
- Set Geometric Surface Orientation
- Set Visual Surface Orientation
- Reverse Surface UV
- Unify Surface Orientation
- Shell Stitch
Tools that modify visual orientation:
Curve Normals
Curve Normals can be displayed using:
Curve Curvature tool
- Normal directions are shown as the green comb display.
- Torsion (if selected) is shown as the orange comb lines perpendicular to the Normal lines (Binormal direction).
Arc Length tool
- N1 - Curve normal direction
- N2 - Curve binormal direction