3DS Max normal map merging with RTT

Valentris

Greetings everybody,

I have a question regarding to normal map re-rendering for a merged group of objects:
The task is:
There is a group of objects, each with itsown normal map, what is needed is to merge them into one, update UVWS and tranfer information from exsisting maps to a new one.
To perform that I attached all objects (with "Match Material IDs to Material" option), added "Unwrap UVW" modifer to it with Map Channel 2 selected, updated UVWs and Rendered to texture with channel 2 selected.
Result is on attached picture - even though information mostly been transered to relocated islands, normal orientation get altered:

All cilindrical part which had "flat pattern" added on original maps (and lookув just fine on renders) now get some roundness on it, elements like screws seem to be losing some normal orientation info.
No combination of Red\Green flipping\swapping provide me with result needed (even so some of them did made render look partially better).
What exactly caused this issue? Are they some additional important steps to RTT process I missing here?

Thanks!

Noren

Have you reprojected this?

Valentris

Noren said:

Have you reprojected this?

No, since I didn't change meshes themselves and only planned to get information from textures, I didn't expected additional projection is needed. If it is, could you please describe steps to be done to get correct normals?

Noren

If you have the unmerged meshes still in the file, put a tiny Push modifier on your merged one (might not be necessary but there was a bug with coplanar faces leading to artifacts) and add the old meshes as source meshes in your projection. Reset the cage (you can add a tiny push just to be sure, but since you already pushed the mesh, that shouldn't be necessary. Render your normal map. Delete or deactivate your Push modifier.

Valentris

Thanks a ton, Noren, that fixed everything.

monster

You don't need to reproject. You can transfer from UV1 to UV2. I've done this successfully several times.

1. Make sure you don't have normal map nodes. Just plug the normal map into the diffuse channel.
2. Set the Self Illum color to 100% or White to remove the lighting transfer.
3. Make sure you are looking at the file on disk, and not the pop up render window. They have different results.
4. Don't rotate any UV islands when repacking.
5. Don't modify the geometry or normals other then attaching them together.

Noren

Yes, that would work as well and would be easier in the case at hand, with the mentioned limitation that you can't rotate your UVs.

Valentris

monster said:

You don't need to reproject. You can transfer from UV1 to UV2. I've done this successfully several times.

Many thanks, tried this method, working just as well.