I did a sofa in 3d with zbrush, made a low poly version, ready for working with unreal engine 4 so with 2 UVs channel.
Then I found some mistake in the anatomy of my sofa so why not export the low poly to zbrush with the move brush arrange a little bit; and surprise, surprise, I export in fbx and re-import into unreal and my uv 0 (where I have my normal map) are now the uv 1 for the lightmap, and where is my original uv for my texture ?
No where !!!
anyway I test to export my mesh from max in obj to test and same thing.
So to conclude zbrush keep only one uv channel.
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If you didn't change your topology it should take you 5 seconds to transfer your extra UV sets in any proper 3D app after having modified the mesh in Zbrush though.
Yes of course bal.
Anyway thanks
I just tried it. Exported a sphere with 2 different UV channels, brought it into zbrush with the fbx plugin, sculpted a bit, exported it back out with the fbx plugin, and imported back into maya.
It only came back in with one UV set called DiffuseUV, this UV set was the more recently created set too, and the little sculpting I did within zBrush changed the UVs, didn't really know if it was any good because it was simply a planar projection.
thanks for trying. looks like it will drop any channel other than the first.
as for your UVs having changed, i suspect it'S not FBX's fault but rather you accidentially had 'suv' - smooth uv, next to the divide button - toggled on:
http://docs.pixologic.com/wp-content/uploads/2013/06/4R6-Geometry.jpg