Two-manifold vs. non-manifold polygonal geometry
 
 
 

Polygonal geometry can have different configurations or topology types in Maya. Understanding the characteristics of these topologies can be helpful when you need to understand why a modeling operation failed to execute as expected.

Two-manifold topology polygons have a configuration such that the polygon mesh can be split along its various edges and subsequently unfolded so that the mesh lays flat without overlapping pieces.

Non-manifold topology polygons have a configuration that cannot be unfolded into a continuous flat piece. Some tools and actions in Maya cannot work properly with non-manifold geometry. For example, the Boolean operations and the Reduce feature do not work with non-manifold polygon topology. The image below shows three examples of non-manifold topology polygons.

The following operations in Maya can produce nonmanifold geometry:

You can convert non-manifold topology polygons into two-manifold topology (including the less obvious case of adjacent faces with opposite normals) using Mesh > Cleanup.

Invalid polygon geometry

Some types of polygon geometry will not work in Maya. Invalid geometry includes vertices that are not associated with a polygon edge and polygon edges that are not part of a face (dangling edges). While Maya does not let you create these types of geometry, it may be possible to import these types from other software applications.