Normal Maps display problem on objects with overlapping UV's

[clau1000]

Hello,

I am trying to get normal maps to display properly in keyshot, namely for objects that have overlapping UV's (for texture saving purposes), and that are mirrored in symmetry. The problem is they don't render correcly for the shell of the UV that is flipped, which is shown in red in the Maya UV Texture Editor.
Of mention is the fact that Mental Ray (in maya) also has this exact problem, and can be fixed by enabling the "Maya Derivatives" option in the MentalRay render settings.

So I made a simple example to test the difference between maya normal map display and keyshot, for overlapped UV's. It's basically a rounded object on a plane (highpoly geometry), that is baked onto a plane (lowpoly geometry), using Xnormal. The plane itself is mirrored on the X axis and has the same uv space attributed to the left and right side of it. Here is a screenshot of the plane's UV's for clarification :



The blue uv shell is the left half of the plane, and the red is the right half of the plane.


Here are the results -
This is the baked normal map, showing the sphere :



Plane with normal map applied, rendered in maya viewport (with high quality and wireframe on) :



Plane with normal map applied, rendered in Keyshot :



Please help, thanks in advance. I have also attached the obj of the plane for testing purposes.I am using Keyshot 4.0 (because keyshot 4.1 has a bug, in which normal maps are displayed as bump maps. This has been fixed in 4.2).

[hbs_steve]

I'm actually noticing this same issue in 4.3.18, did you ever resolve it?

[thomasteger]

Yes - works great in 4.3.18.

Make sure you check "normal map" in the bump map tab inside the material editor.

[hbs_steve]

Hi Thomas, thanks for replying.

I've got that checked, and it's working properly for half of the model, the problem is that areas in the UVs that are flipped and overlapping are rendering improperly. 

[thomasteger]

Can you share an example?

[hbs_steve]

Here's a screenshot out of Keyshot with the normal map applied to the Imported model. Cropped it to show the areas where it's most noticeable - on the thighs and feet. As you can see, one side is correct while the other, the normal map is reversed, with crevices and cracks appearing as raised areas, and vice versa. It's the same issue that clau1000 posted about. I did just update to 4.3.18, so if it's something I could possibly solve by rolling back to an earlier version, I'd be willing to try that.

[fred2303]

I can comfirm that this display problem is still present in the current version.

Is there a fix planned for the next version?

[thomasteger]

It appears to be a case of flipped surface normals in the Maya file. Can you try and flip the normals (inside Maya) to see whether this fixes things?

[fred2303]

Ive checked and the normals on the mesh are alright and the normal map displays perfectly with all other shaders, renderer and game engines.
Also ive checked with the new keyshot 5 version and the problem is still there.

[Marco_Hasmann]

Seems like this problem is still occurring to me in KS6; the parts with mirrored UVs has the Green Channel inverted; the problem persists with both overlapped and non overlapped UVs; is there a fix to this?

Tried inverting the green channel in PS, but that just inverts the faces where the problem appears; any solution?

[Marco_Hasmann]

The only "temporary" problem that I managed to find atm is importing the left and right sides as separate objects; and flip  the green channel on the the mirrored face; this means I have to setup 2 different materials :/ kinda annoying; isn't there a workaround or some way for keyshot to do it on his own?