Unable to get reliable normal mapping of uv islands

[Trasna]

I've posted on this before and had the problem resolved, I've even resolved it myself since. The problem is that resolving the issue seems to be completely random in nature and the next sculpt I make will suffer with the same problem, I'll then spend hours re-baking normal maps  and carrying out any number of different attempts at fixing it and then suddenly it will bake ok, but I am then unable to determine what I did differently to make it work.

 

I am coming to the conclusion that this is not workflow but a bug in the normal mapping code as it seems impossible to reliably get the results required or identify the one thing that stops this problem happening.

 

Here is an image of the issue ......

 

 

3D Coat is doing a perfectly fine job of creating a normal map of the fine details that have been painted on, what it is screwing up continually is the UV islands.

 

Where the mesh has been split into UV islands for unwrapping (the picture above just being an auto unwrap) the normal map is incorrect where uv islands join with one another. So when the model is pieced back together you get the patch work effect of your uv islands all over the render. Clearly this is nothing to do with UV cage issues, global space or sizing of the sculpt (the mesh is uniform, scale of 1, a good size for baking etc etc). I believe it is a bug in the normal baking of uv islands as I can't come up with a reason as to why 3D coat would do this with uv islands other than it being a bug.

 

While I have managed to resolve this the methodology to do so is completely unclear, I think I've just got lucky the times it has worked ok. 

Does anybody know of a workflow step I may be missing here that makes uv islands not normal map correctly at the seams?

It's almost like the normals are flipped from one uv island to the next.

Edited October 8, 2015 by Trasna

[Trasna]

Wow, why is it when you finally decide to post about a problem you then find the issue.

 

The p[roblem UV islands are indeed flipped and I found them using the complex checker in the UV room. My bad.