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Degenerate Tangent Bases

So I've getting the Degenerate Tangent Bases error on one of my meshes. I got it to not have weird distortion on the texture by generating a light map and changing the light map coordinates to 1. Even after that I'm still getting the degenerate tangent bases bases error. It looks a little strange compared to the rest of the meshes don't have the error but it's not as bad as it was. Now the lighting is showing up weird and there are strange lines going across the mesh in random places. Increasing the light map resolution hasn't worked and I've mucked with a bunch of settings trying to fix it so I'm kind of at a loss as to what to do to get rid of the weirdness. alt text

Also another issue I'm having, that I thought I should mention because I don't know if it has anything to do with this, is that the lighting gets weird after building. Even though the lights are static and the meshes are static and all the meshes have light maps. I'm only using diffuse and spec maps. Not sure if that has anything to do with it.

Before build: alt text

After Build: alt text

Its seems to loose some reflectivity, luster, and some light coloring as well, and I have no idea what's causing that.

Any help would be appreciated, I'm kind of at a loss here. Thanks.

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asked Oct 18 '14 at 09:22 PM in Rendering

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avatar image neighborlee Dec 29 '14 at 09:35 AM

I have the degenerate tangent base error too, yet instead of stray lines, I get weird blotches ( highlighted tris I think ?) of 'grey' areas. This weird look is not present in static mesh editor, as there mesh looks perfect.

Thx anyone .

latre lee

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4 answers: sort voted first

Hi all,

Degenerate Tangents are directly related to your UV and how the mesh is laid out in the UV space.

With 4.7 MikkTSpace was added to the engine.

Here is a simple box with an inset face and extruded center.

MikkTSpace: alt text

Old UE Code: alt text

Basically, the "tangent" vector points in the direction of the U texture coordinate and the "bitangent" (or "binormal" depending who you ask) points in the direction of the V texture coordinate. That coordinate space provides a mapping from "texture space" to "object space" which is what lets tangent space normal mapping work. That's a very simple explanation.

In 4.8 there will be an option to disable this in the Build Settings of the Static Mesh Editor where necessary.

Thank you!


253538-mikk.png (242.6 kB)
253539-ue.png (240.2 kB)
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answered May 06 '15 at 02:22 PM

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Tim Hobson ♦♦ STAFF
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For the reflection and the likes you need a sphere reflection capture. https://docs.unrealengine.com/latest/INT/Resources/ContentExamples/Reflections/1_4/index.html

As for tangents, those look at the first UV, (and can have the worst seams especially for normal maps) so make sure that thats fine. could you show us an image of the uv map for that texture/amterial?

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answered Oct 19 '14 at 11:34 AM

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avatar image EarlWindsorXII Oct 19 '14 at 06:07 PM

Okay cool thanks, I'll put that in.

Here's a screenshot of the UVs: alt text

I'm not sure why it would be this mesh specifically giving me the error because I have a lot of other meshes that have overlapping UVs on the texture and they're perfectly fine.

Its also probably worth mentioning that when I change the lights to stationary all the issues disappear. It just hurts performance. Only the static lights are having the issue for some reason.

avatar image Luos Oct 20 '14 at 01:23 AM

Should work, perhaps one is mirrored?

avatar image EarlWindsorXII Oct 20 '14 at 08:31 PM

Doesn't seem like it. Not sure what else to check.

avatar image Luos Oct 21 '14 at 01:14 AM

Smoothing groups is the only thing I can think of, or a stray vertex somewhere..

No clue. If you are around tomorrow and have skype add me and we could discuss it in person a two people tend to get more done than one. (Nick: Luos_83)

avatar image EarlWindsorXII Oct 22 '14 at 03:13 AM

There doesn't seem to be a missing vertex or any ngons or anything like that. Unless I'm doing smoothing groups wrong I'm not sure if that's it either.

Okay. Sorry, I didn't read your response until a few hours ago. Tuesdays are kind of a busy day for me. If you're available any other time let me know.

Thanks for all your help!

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check UVW mapping alignment for instance in max under UVW map go to alignment then view align now if the shape of the UVW mapping align doesn't match how your object is shaped then correct it . it should work .

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answered Apr 03 '15 at 05:24 PM

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Phoenix Flame
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I ran into this yesterday as well. In my case there were 2 things that I fixed in the mesh and it went away.

  1. I was using a mirror modifier (in blender) and one of my objects went over the median/center point, so the object and the mirror overlapped. I lined up the edge face so it ended at the center point, removing the overlap.

  2. I removed the faces that were up against other objects. ie, the faces you can't possibly ever see anyhow.

My mesh when imported also looked kind of funny because it was painting the inside face of objects that had a bevel on them. Adding a solidify modifier fixed that.

I hope that helps.

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answered May 06 '15 at 11:56 AM

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