Subdivision models naturally have more polygons than realtime models because of holding edges and good edge flow overall. However, it’s important to realize that a really well-made subdivision model often has fewer polygons than a non-subdividable model.
The following two images show a model of a Dimplex grill. On the left is the original model an artist created. He tried to make the model so it didn’t need subdivision when used as a background or mid-range object. But the model had no holding edges, so it couldn’t be subdivided for close-ups. The model on the right, however, was made especially for subdivision, with fewer segments along the side. With no subdivision the model works for background shots, at Level 1 subdivision for mid-range shots, and Level 2-3 for closeups. The subdividable model, at the base level, has fewer polygons than the original model.
Original model. Too many segments and no holding edges.
Subdividable model. Fewer side segments, holding edges, fewer polygons overall.
Another example is this skull model. The original model (left) has a high number of polys. The same model can be represented with a much lower poly count (middle) with the option to subdivide (right). This gives the customer more options while keeping the base poly count fairly low for background use.
Recently we’ve had a lot of blog posts about how to get your 3D models certified for CheckMate Pro v2. For your convenience, here is a list of blog posts and resources that can help you pass the specification.
To help you pass CheckMate Pro v2 certification faster for subdividable models, here is a summary of the topology requirements. Please refer to the links for more detailed information, and also to the CheckMate Pro v2 Checklist.
Grid pattern for edges wherever possible. By this we mean have as close to 90-degree angles between edges as possible while still retaining the shape and flow of the model. The grid can go diagonally or turn corners, as long as it retains a grid pattern throughout the model as much as possible.
Supporting edges to hold shape during subdivision.
Please note that CheckMate Pro v2 Tool 2 checks only for points specific to Pro v2. You will still need to run Tool 1 to check for specification points brought forward from Pro v1 such as quads, isolated vertices, etc. Tool 1 is the Pro v1 script, renamed to Tool 1 to differentiate it from the new script for v2.
The CheckMate Pro v2 specification requires subdividable models to have excellent edge flow. Good edge flow means you can easily select edge loops and rings, and the model subdivides extremely well. Your 3D application includes tools for testing these features.
Testing Edge Flow
With your model at the base level select an edge at random, and use your software’s built-in tools to select loops and rings from that edge. Repeat the test for several more edges on your model. If most of the loops and rings continue along the object, then your model has easily selectable edge loops and rings.
Here is a quick guide to selecting edge loops and rings in three of the major 3D applications. Refer to your software’s Help system for more information.
3ds Max: Select an edge from an Editable Poly and click Loop or Ring in Selection rollout.
Maya: Select a loop by double-clicking an edge; select a ring with Polygons menu > Select > Select Edge Ring Tool.
Cinema 4D: In edge mode, hold down V and choose Select > Loop Selection or Ring Selection.
If you are submitting a subdividable model, it is essential that you test the subdivision before you submit the model for CheckMate Pro 2. After subdividing your model, check for:
Pinching. Indicates poor edge flow, coincident or near-coincident vertices that need to be welded, or tiny polygons that must be collapsed.
Whirling patterns of edges. Indicates poor edge flow over a substantial area.
Drastic shape change. Indicates that the base model needs more detail or holding edges.
After correcting your base model, look at it to make sure a customer can use it without subdivision if they wish to do so. If the model looks great with subdivision but the base model has hidden overlaps and strange pulled shapes, the model will not pass CheckMate Pro v2. The base model with no subdivision must be usable on its own.