Display Face Normals
Maya 2012 Tutorial
How to Display Maya Polygon Object Face Normals
The direction of the face normals specifies which faces are pointing forward. Normals are also used to calculate smooth shading for two connected faces. By default if the angle between two faces is less than 30 degrees, the joining edge appears rounded.
In this example, we will create a cylinder and reverse some of it's faces. The object will be converted to a one sided object before rendering so you can see what happens if you have a reversed face.
To correct an object with reversed faces, select the backwards faces and choose Normals > Reverse from the Polygons menu set.
Add a polygon cylinder to the workspace by choosing Create > Polygon Primitive > Cylinder (include options).
In the options, set the Axis Divisions to 6. Click the Create button to add your cylinder.
To view the object normals, select the object and choose Display > Polygons > Face Normals. A normal line appears in the middle of each of the object's faces.
To adjust the normal size, choose Display > Polygons > Normals Size.
Tumble your object in the perspective view (Option/left mouse drag (PC - Alt/left mouse drag) and notice that all the normals are pointing outward to indicate that the front faces are pointing out.
Right-click the cylinder and choose Face.
Click one of the top faces, then Shift click every other face on the top of the cylinder. You should have three faces selected. To activate Smooth Shade view, press the 5 key.
Choose Normals > Reverse from the Polygons menu set. The normals for the selected faces now point in the down direction.
Render your scene by clicking the Render Current Frame icon. The object should look fine.
Right-click the cylinder and choose Object Mode, then select the cylinder.
Open the Attribute Editor, pCylinderShape tab and click the Render Stats section.
Deselect the Double Sided checkbox and click the Render Current Frame icon. Some of the object faces are no longer visible because they are reversed.