Geometry

2.1.1 No isolated vertices

2.1.2 No coincident vertices

2.1.3 No coincident/coplanar faces

2.1.4 Face normals point outward - By "outward" we mean the appropriate direction for correct rendering, with no normals incorrectly flipped.

2.1.5 No empty objects - All objects should have geometry or splines or be null/control helpers. No "empty objects" that have names but nothing else permitted.

2.1.6 Geometry must not have open edges or borders that cause see-through cracks in the model when rendered.

2.2 Topology

2.2.1 Quads and triangles only

2.2.2 Mostly quads - The model must use quads as much as possible. A range of 10%-20% tris is sensible for most models, but some will call for a higher percentage to form sensible topology. Models are inspected manually to ensure a sensible quad/tri ratio is maintained.

Note that realtime models will often have a much higher percentage of triangles to meet the requirement of "minimum geometry possible to form the object".

2.2.3 Clean edge flow: Model must have the best possible edge flow, with sufficient geometry to meet these requirements without superfluous geometry

2.2.3.1 Subdividable Topology: Model can be cleanly subdividable for higher detail and still retain shape of model.

2.2.3.2 No poles with more than 5 edges on the model

2.2.3.3 Holding/support edges present to retain shape after subdivision

2.2.3.4 Exceptions:

2.2.3.4.1 Exception for very small, insignificant objects within the scene: Such objects do not have to meet the criteria above. Objects such as screws, bolts, rivets, wires, and other objects which are very small in comparison to the overall model size, do not have to follow the Clean Edge Flow rules.

2.2.3.4.2 Exception for one-sided objects with opacity map: Objects that represent a thin real-life object as a one-sided object, where the shape of the object is depicted via an opacity map, do not have to follow the Clean Edge Flow rules.

Examples of this exception are leaves, petals, decals, paper, cloth. This exception does not apply to fully three-dimensional objects such as thin boxes.

2.2.3.4.3 Exception for realtime models: Models intended for game engines, realtime display, or background elements must have the lowest number of polygons possible while still retaining the model's shape, but do not have to conform to the points above. For such models, a high percentage of triangles is allowable, provided they are necessary to make the model shape with the lowest number of polygons possible.

2.2.4 Crease value: 3ds Max and Maya only: Value of Crease parameter must be 0 for all edges.

This requirement ensures that a subdividable model, when converted to other formats, will retain the same shape when subdivided. If the model is a realtime model (not subdividable), there is no reason to have a Crease value other than 0.