Bake groups and exploded bakes

Bake groups pair each low-poly part with its own high-poly part, so the baker never projects one part onto another. Marmoset describes them as "special folders with slots for high and low poly meshes" used "to isolate different elements of your model to prevent errors at intersection points" (Marmoset Toolbag documentation: Bake Groups). An exploded bake reaches the same goal by physically moving the parts apart before baking.

#Why it matters

When parts touch or sit close together, rays from one part travel into the next. Adobe: "Sometimes the rays go too far and hit the wrong geometry" (Substance 3D Bakers documentation: Mesh parts bleed between each other). The result is ghost copies of bolts printed on panels, or smeared edges where a handle meets a lid. On Polycount, EarthQuake's rule is: "Anything that is going to give you intersection errors should be exploded" (Polycount: Exploded Mesh or not exploded mesh?).

#Three ways to separate parts

1. Bake groups (Marmoset Toolbag). Each group has a High and a Low slot; you can use "as many or as few groups as you like" (Marmoset Toolbag documentation: Bake Groups). The quick loader builds the groups from object names, and is not case sensitive (Marmoset: The Toolbag Baking Tutorial).
2. Matching by name (Substance bakers). Low and high parts are paired by suffix, by default _low and _high, to "avoid geometry bleeding over each other" without "having to move away meshes" (Substance 3D Bakers documentation: Matching by Name). It is off by default and case sensitive (Substance 3D Bakers documentation: Matching by Name).
3. Exploding. Move each low/high pair apart by the same distance so no cage overlaps another part. Kon Artist: "If you don't exploded your mesh you can get projection errors or burn through" (Polycount: Exploded Mesh or not exploded mesh?). This works in any baker, including free ones without grouping.

Groups and name matching are usually faster than exploding because the model stays assembled. In a 2017 thread where another poster suggested exploding, EarthQuake recommended Toolbag's bake groups instead, set up automatically with "name matching" (Polycount: Baking of multiple high-poly onto multiple…). In 2018, GreyJke made the same point about Painter: matching by name means you do not have to explode (Polycount: Recommended software for baking…).

#Contact shadows

Separating parts also stops them from shadowing each other in the ambient occlusion bake. JamesWild warns an exploded bake "might look less cohesive as parts won't cast shadows on one another" (Polycount: Exploded Mesh or not exploded mesh?).

Ways to restore contact shadows:

• Marmoset's Ignore Groups. This option "will cast AO between different bake groups" while keeping normals isolated (Marmoset: The Toolbag Baking Tutorial). You can still move a part away, such as a magazine, so it does not receive AO from other groups (Marmoset: The Toolbag Baking Tutorial).
• Substance's Self Occlusion setting. "Always" matches the low poly with every high poly, while "By Mesh Name" filters them (Substance 3D Bakers documentation: Ambient Occlusion from Mesh). Leave it on Always if you want contact shadows between parts.
• A second AO bake of the assembled model. EarthQuake suggests "a second ao bake from the lowpoly to get that inter-mesh-chunk ao" (Polycount: Exploded Mesh or not exploded mesh?).

#Common mistakes

• Names that do not match exactly, especially with case-sensitive matching (Substance 3D Bakers documentation: Matching by Name).
• Exploding by different distances for low and high, so they no longer line up.
• Losing all contact AO and never adding it back (Polycount: Exploded Mesh or not exploded mesh?).
• Too many tiny groups. EarthQuake's alternative for a seamless look is to "use fewer mesh chunks", merging parts that do not need separation (Polycount: Exploded Mesh or not exploded mesh?).

#Related terms

baking · bake cage · fixing baking artefacts · the high-to-low workflow · ambient occlusion · naming conventions

#Further reading and watching