Mirror Heads by Tracing 3D Geometry for Blend Shape Facial Animation
by Brian Immel
This tutorial covers the basics of tracing geometry in 3D space. The basic premise is to make a mirrored duplicate of the shape you are trying to recreate on the other side of the face for facial animation.
1. Duplicate the base head (without any expression or mouth shapes) two times. Move each head apart on TranslateX by 1.
2. Name each head Brow_Up_L, Brow_Up_R.
3. Model the head labeled Brow_Up_L to the shape you need. In this case, I’ve modeled the left brow raise.
4. Select the head labeled Brow_Up_L and duplicate it. Name this head Trace_ME.
5. Select the Trace_Me head and type in –1 for ScaleX. This will make the head appeared to be mirrored. We do not want to use this head for the right brow raise head because it will not work. Maya’s Blend Shape system works on a per vertex basis, not by the entire shape of the objects involved in the surface. By mirroring the geometry (-1 on ScaleX) does not affect the vertices, it just flips the orientation of the entire object.
6. Move the Trace_Me head to have the same exact location as the head labeled as Brow_Up_R.
7. Now we want to use the Trace_Me head as a template to model the other brow. Select the Brow_Up_R head and go to vertex component mode (right-click-hold over the geometry and select vertex).
8. Create a layer and place the Trace_Me in that layer. Double-click this layer, name this layer Trace_Me_Layer, select a yellow color chip and hit the Save button.
9. Change your view to wireframe by hitting the keyboard shortcut 4. Notice how the vertex components are light blue and the unselected head (Trace_Me) is yellow). We want to move the vertices of Brow_Up_R to match the exact location of Trace_Me geometry. Refer to Figure 5 at this point to see where we should be.
10. Turn on Snapping to Points in the Snapping options.
11. Carefully select one vertex at a time and move it to the corresponding location of the Trace_Me head. The best strategy for matching these vertices up is to start on the outside and work your way around the outside slowing moving in.
12. Go to the Outliner (Window > Outliner…), select the Trace_Me head, and delete it. Now we have a perfectly matched and mirrored head to the Brow_Up_L head.
13. Set up a Blend Shape between the brow heads and the base head to test the blending abilities of the brows. Look for areas around the center edge that may travel to far and too fast when both blend shapes are active. If the center edges/vertices to travel too much, leave the blend shape attributes active (set to 1 on both Brow_UP_R and Brow_Up_L) go back and make any necessary adjustments with the brow heads. Refer to Figure 8 to see how the brow should move.
Happy modeling!
