Normal Maps, polygon tangents and their relationship to uv[0]...

[Anonymous]

Is there a way to directly edit polygon tangents in Maya? I'm able to display them but I can't seem to find any tools for correcting / adjusting them like I can in other applications. It also seems like maya is using the default UV map (uv[0]) to generate these polygon tangents that then get used in normal mapping.

This causes a problem for normal maps if the default uv map only has some polygons uv-mapped (as is sometimes the case when using multiple UV sets to stack textures together with a layered shader) so my next question that follows is whether or not I am able to re-order uv sets or tell maya which one to use as uv[0]. There seems to be no direct way to tell maya WHICH uv set to use as 'the default' uv map.

In other applications the 'under the hood' procedure for generating polygon tangents is to use polygon vertex normals + polygon tangents (often grabbed from uv space) + bitangents. In most other 3d apps I have used even if polygons are missing from uv space the polygon tangents are still calculated correctly and normal maps work as expected - in maya unmapped polygons of a given mesh in uv[0] create broken polygon tangents and thus broken normal maps.

In short:

1. Is there a way to adjust polygon tangents in maya or recalculate them (similar to how one might fix vertex normals)

2. If I have a bunch of uv sets in a mesh...is there a way to directly choose which one maya sees as 'default' (uv[0])?

Thanks.

[sean.heasley]

Hi @Anonymous

Maya default to the "original" UV maps every time. So for example, when you first open the UV editor/set editor you have a "map1" uv set. This is the default UV set and can not be deleted so if you were to rename it you'll just need to remember that this is your original UV map.

As for the polygon tangents, I believe you want to use the Vertex Normal tool which can be found under Mesh Display->Vertex Normal Edit Tool.

While you can't select faces, this tool allows you to select the vertices and manipulate their normals to the desired result.

Please let me know if this helps or if you need any more assistance!

If one or more of these posts helped answer your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.

Kudos are greatly appreciated. Everyone likes a thumbs up!

[sean.heasley]

Hi @Anonymous

I'm just checking in again to see if you need more help with this. Did the suggestion I provided yesterday work for you?

If so, please click Accept as Solution on the posts that helped you so others in the community can find them easily.

[Anonymous · Accepted solution]

Hi Sean...thanks for the replies. So I've determined through testing that maya does indeed use whatever uv map is at the top of the uv set stack as a part of calculating polygon tangents. If this top set only includes partial uvs, normal mapping will be broken despite there being additional sets below with proper uvs which are being used to apply the normal map.

I found and tried the the vertex normal edit tool which does indeed enable me to rotate tangents - so thanks for that - but I was unable to fix the tangents in this way.

What ended up fixing the issue, however, was reordering the uv set stack so that a complete uv set of my choosing was at the top of the stack. Since there is no tool in maya to do this (hopefully that is a feature that can be added to the uv set editor - which one might expect would allow you to move the sets up and down relative to one another) I reordered manually by copying the 'top' uv set to new sets and deleting until my desired and complete uv set was at the top.

This is sort of hard to grasp without pictures explaining what's happening and when I'll have some time I'll post those - because this is most definitely a bug or at least an oversight in how maya is calculating normal map polygon tangent info. The overall point is that proper and functioning polygon tangents for normal maps depend on the actual ORDER of uv sets for a mesh using multiple linked uv sets.

-John

[Anonymous · Accepted solution]

Just a heads up that this particular problem is a rare problem and seems to happen when an asset is UV'ed in another app with multiple sets, brought into maya, and for whatever reason uv[0] gets assigned to a partial uv set. A workaround is just to never ever only partially uv your object and this specific issue should never ever arise.

[sean.heasley]

Hi @Anonymous

Nice catch with that issue! Thanks as well for explaining what you did to solve this and marking it as a solution!