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Subdivision Levels

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About Subdivision

Subdivision is probably familiar to most users of modeling programs; it increases the polygon count of a model by replacing each polygon with multiple polygons. The most commonly used subdivision scheme is the Catmull-Clark method, which also moves vertices as it subdivides, so that a low-resolution cage can give a high-resolution smooth surface.

ZBrush offers an additional powerful feature when using subdivision with polymeshes; a polymesh retains a “subdivision history.” To put it another way, each time a polymesh is subdivided, the geometry from the previous polymesh is remembered, all the way back to the original polymesh. So a subdivided mesh can have multiple levels of subdivision, equal to the number of times it was subdivided plus one for the original level.

You can move back and forth between these subdivision levels as you model; if you need to make ‘large-scale’ changes to an object, such as raising a significant portion of the surface, you can do it at a lower subdivision level where the model’s polygons are relatively large (more of a ‘cage’) while fine details can be sculpted at a high subdivision level. In either case, changes will be propagated across all levels, so sculpting geometry at one level does not lose the work you’ve done at another level.

To understand the power of this ability, consider the following example. At a low subdivision level, you sculpt a polymesh plane so it appears as rolling hills. Then, at a high subdivision level, you add a “bumpiness” that gives the appearance of rocks, dirt, etc. But it then turns out that instead of rolling hills, you need a flat plain. What to do? Well, you go back to the low subdivision level and use the sculpting tools of ZBrush to smooth out the hills. Finally, when you return to the high subdivision level, you’ll find that all of the fine “bumpiness” detail is still there. That work wasn’t wasted!

Subdivision levels are also used to generate bump, displacement, and normal maps. Detail is added to an object at a very high subdivision level (possibly with many millions of polygons). That detail can then be compared against a lower subdivision version of the same model to generate a displacement or similar map. Once generated, that map can be taken to an external program and applied to the lower-poly-count model to give a detail effect almost indistinguishable from the high-level sculpting in ZBrush.

 

Example Workflow

An example workflow is as follows:

  1. Import a low-resolution base mesh.
  2. Subdivide it several times, possibly taking the polygon count into the millions.
  3. Sculpt in fine details at the highest level of subdivision.
  4. You may then decide that some of the base geometry is unsatisfactory; for example, your hero’s muscles should be larger than they are.
  5. So, switch to the lowest level of subdivision, and sculpt in those bulging biceps.
  6. Now, when you go back to higher levels of subdivision, the throbbing veins and almost invisible muscle striations will still be visible!
  7. Now, go back to your lowest subdivision level, generate a normal, displacement, or bump map, based on your highest-resolution version of the model.
  8. Export the modified lowest-resolution model to preserve the sculpts you’ve made on it.
  9. Use the modified model and the new maps in your external program.

 

Smoothing UVs

If the Smooth UV switch is turned on then any UV coordinates will be smoothed when the next Divide or Edge Loop action is performed.

  • When the Smooth UV mode is enabled, the UV smoothing is automatically updated when the subdivision levels are changed. This re­moves the need to manually re-import a smooth UV version of the model or constantly use the ReUV command.
  • When SmoothUVs is enabled for generating maps, all UV borders will remain frozen when smoothing.

 

 

 

Subdivision controls

The Subdivision controls are in the Tool > Geometry sub-palette.