Lightmass AO vs Material AO map difference?


I’m wondering what’s the difference between [ambient occlusion baked from the lightmass] and [ambient occlusion maps baked from a 3D software that can be linked in the material]?

For static meshes, should I use a material with an AO map, while still let the lightmass bake another AO? Do they add up? Or one is redundant since one just overwrites the other?

Material AO is most useful for cavity maps, or really tight AO. Lightmass AO or screen space AO should be the one capturing large AO detail. You don’t want to stack up too much AO doing the same thing.

Zac has the right idea.

Lightmass AO is mostly intended to be used for non-lighting effects such as placing moss or moisture in the corners of intersections of rocks. It is a method to get a more ‘custom’ painted feel for meshes that have been jammed together. It was not really intended to take that node and plug it into material AO, but there should also be nothing stopping you from trying it. But if you rebuilt the lighting, the lightmass AO was already used internally by the static lighting.

Thanks for answering.

But the lightmass AO is also able to darken/occlude cavities with the knowledge of mesh geometry or normal map. If the lightmass AO can occlude cavities AND occlude larger AO details, then why should the material AO even be used?

The texel density of a lightmap shouldn’t be anywhere close to the texel density of a texture.

Also it’s useful for characters or moveable assets.

So lightmass AO is suitable for larger details but not tiny cavities that can’t tolerate small lightmap resolutions. Increasing lightmap resolution to compensate for the lost detail of tiny cavities would however be an overkill. Thus material AO is used instead. Am I understanding this correctly?

MaterialAO also works for movable objects like characters or vechiles.