Symmetric Modeling with an Instance Object
Maya 2012 Tutorial
How to Create a Symmetric Object Using an Instance Object in Maya
Modeling symmetric objects can be simplified by modeling only half the object. The other half is an instance object that mirrors the original geometry.
Add a polygon cube to the workspace by choosing Create > Polygon Primitives > Cube (include options).
In the options set the Width, Height and DepthDivisions to 2. Click Create to add your cube.
In the front view, right-click the object and choose Face from the menu.
Marquee select the left have of the cube and press Delete.
Right-click the object and choose Object Mode from the menu.
Select the object and choose Edit > Duplicate Special (include options).
In the options, set Geometry Type: Instance, Scale x to -1 and Number of Copies: 1. Click Duplicate Special to add your instance object.
Right-click the original object and choose Face from the menu.
Select one of the end faces and choose Edit Mesh > Extrude from the Polygons menu set.
Click and drag the extrude arrow and notice that both shapes are affected.
Press the q key to exit the Extrude tool, then right-click the object and choose Edge.
Click one of the upper edges and use the Move tool (w key) to move it in the y direction.
More Ways to Create Symmetric Objects
In addition to instance objects you can also create symmetric objects by mirroring or activating the Move tool's Reflection mode. For more information, see topics, Symmetric Modeling with Mirroring and Symmetric Modeling with Move Tool Reflection Mode.
Making Seam Points Coplanar
If you are modeling an object by moving vertices (i.e., a character's face), you can easily end up with seam points that are non-coplanar. To fix the problem before mirroring, right-click the object and choose vertex. Marquee select all the seam vertices and choose Window > General Editors > Component Editor. Click-drag all the values in the vertex.x column and enter a value (i.e., 0). All the vertices now have the same x value.
Don't Forget the Pivot Point
In this example we mirrored the object by setting the scale to -1 (Step Seven). The mirroring worked because the object's pivot point was at the left edge of the object. To use this trick the object's pivot point needs to be located at the mirror edge. For more information on moving an object's pivot point, see topic, Moving Object's Pivot Point.
Combining the Two Halves
Once you are finished modeling, you will need to combine the two halves of your object. To join the two objects, choose Mesh > Combine from the Polygons menu set. To merge the vertices and edges, choose Edit Mesh > Merge.