From ZBrush Info
The Tool:Geometry subpalette contains controls that modify the mesh geometry of a 3D model. This subpalette also appears with primitive and ZSphere models, but is substantially different in form and function, so we treat it separately
Concepts
Subdivision Modeling
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.
An example workflow is as follows:
- Import a low-resolution base mesh.
- Subdivide it several times, possibly taking the polygon count into the millions.
- Sculpt in fine details at the highest level of subdivision.
- You may then decide that some of the base geometry is unsatisfactory; for example, your hero's muscles should be larger than they are.
- So, switch to the lowest level of subdivision, and sculpt in those bulging biceps.
- Now, when you go back to higher levels of subdivision, the throbbing veins and almost invisible muscle striations will still be visible!
- Now, go back to your lowest subdivision level, generate a normal, displacement, or bump map, based on your highest-resolution version of the model.
- Export the modified lowest-resolution model to preserve the sculpts you've made on it.
- Use the modified model and the new maps in your external program.
Edge Loop Modeling
The edge loop modeling controls are found in the Tool:Geometry subpalette, and are the basic way in ZBrush by which low-resolution polymeshes may be manipulated to add polygons at particular points. For example, if you were starting with a low-resolution mesh of an animal of some sort, you might use edge loop modeling to create further polygons in facial area you felt would demand high levels of detail. Once these polygons were in place, then subdividing the model would result in a much higher subdivided polygon density in those areas.
Subdivision Modeling Controls
Divide: Subdivides an object, i.e. causes each quad to be replaced with four quads to give a higher-resolution geometry. (Tris are handled in a similar way). This gives a higher-resolution object with which to model.
Lower Res: In a multi-resolution polymesh, reduces the displayed resolution level by 1. (Hotkey D).
Higher Res: In a multi-resolution polymesh, reduces the displayed resolution level by 1. (Hotkey d).
SDiv: Slider that allows you to move to any display resolution of a multi-resolution polymesh.
Cage: When turned off (the default), edits made at high subdivision levels will also displace vertices at lower subdivision levels. This is usually the best way of doing things, as it gives the smoothest and most predictable results. When turned on, ZBrush will attempt to keep lower-level vertices from moving as higher-level edits are made.
SSmt: See online help.
Del Lower: When working with a polymesh model that is being displayed at level n, this will cause all levels lower than n to be deleted, and the model shown at level n will then become the new level 1 model. You can use this if you decide the lower levels of subdivision are no longer necessary.
Del Higher: When working with a polymesh model that is being displayed at level n, this will cause all levels higher than n to be deleted, and the model shown at level n will then become the new highest level model. This will discard all of the fine details that require higher levels to display. You can use this if you decide that the work you've done at higher levels needs to be completely redone.
Reconstruct Subdiv: Given a model being displayed at its lowest subdivision level, this attempts to construct a lower-level model such that subdivision of that model would give the model currently being displayed. If this is successful, the displayed level 1 model becomes the level 2 model, and the newly created model becomes the level 1 model. Reconstruction of a lower-level model cannot always be done. UV's are needed to do this, so you may need to go to Texture->EnableUV's->AUV.
Divide: (Hotkey Ctrl-d.) The fundamental operation for working with multiresolution models. When pressed, adds one more level of subdivision to the current polymesh.
Note: Subdivision can be used in conjunction with masking; this will cause only unmasked portions of a model to be subdivided. (In some cases, masked portions will also undergo some subdivision, but it will result in a much smaller increase in the number of polygons in the model.) This is a valuable feature when working with a very high-resolution model in which you need to add additional local detail, as it allows you to increase polygon density in a localized region, rather than subdividing the entire model and thus multiplying the polygon count by four.
Smt: Normally, when subdivision occurs, the object becomes smoother, i.e. sharp edges become smoother. When Smt is off, this will not occur; all edges will retain their original sharpness.
Sym, Mrg, IExtr, ReFit, Suv, I-Grpm O-Grp: See online documentation.
Edge Loop Modeling Controls
Edge Loop: In a polygon mesh some of which is hidden, creates new geometry on the borders between the visible and invisible portions of the mesh. This is a generalization of the edge loop functions found in many other 3D packages, and is discussed in more detail in documentation dedicated to this topic.
Crisp: When active, pressing the Edge Loop button will cause extruded polygons to be very thin in their extruded dimension. As the model if further subdivided, this will give a crisp (sharp) edge, as opposed to the smoothing typical of subdivisions.
Disp: Controls how far edges are displaced with Edge Loop is pressed.
DelHidden: Deletes all hidden polygons in a model, leaving only the visible portion.
Crease: Applies a tag (visible as a dotted line) to edges bordering hidden polygons. Such marked edges are less affected by subsequent subdivision smoothing, and so come out looking sharper.
Note: There is no industry standard for this kind of tagging (other programs have their own similar but proprietary methods), so if you mark a creased edge this way, that creasing will not be exported when exporting a model with such creases--use the Crisp feature above if you need to export creases. However, Crease can still be very useful when generating displacement etc. maps.
CreaseLvl: Controls how many more times a creased edge will be subdivided before it starts being smoothed, which basically means that the higher this setting, the sharper the edge.
UnCrease: Removes crease tags from edges that are on the border of hidden polygons.
Other Controls
Reproject Higher Subdiv: When sculpting (particularly with some of the newer brushes in ZBrush 3), certain areas of your model may end up with a highly unequal distribution of polygons.
Reproject Higher Subdiv can be used to relax such areas.
To use it:
1) Sculpt your model at the highest subdivision level.
2) Go to a lower subdivision level where the polygons have a more even distribution. You may want to sculpt a bit at this level to get an ideal distribution.
3) Activate Reproject Higher Subdiv. ZBrush will compute a new distribution of polygons at the highest subdivision level that is more relaxed (even) while still preserving the geometry of the model. Depending on the complexity of your model, this may take some time.
4) After the computation is done, your model will be displayed at the highest subdivision level.
Delete Hidden: In a partially visible mesh, deletes those polygons that are not visible.
Crease: Cause an edge to be marked as a crease; this will be indicated as a dotted line drawn along the edge. This marks all edges of the visible area of a partially visible model as creased. Creased edges will appear sharper than other edges, as the model is subdivided.
CreaseLvl: Controls the sharpness of creased edges. Higher levels result in sharper edges.
InsertMesh: Allows you to choose another mesh which will then be added to, and become part of, the current mesh. As of ZBrush 3, this feature is mostly obsolete; use the features of the Tool:Subtool menu instead.
