Normal Map, Tangent Binormal on Mirrored Objects

[shivanangel]

After reading a while on Normal maps for other engines, I found that this is a common problem when the attributes do not contain a 4th 'W' component indicating mirrored portions of the mesh. Apparently, other engines such as Unreal and CryEngine are able to determine the flipped normals and have them flipped by multiplying by the W coordinate ( +1 or -1).

Fixes for other engines (Unity in this case) referred to exporting the binormal and tangent vectors through the FBX file format.
In this case, I don't see anything that can be similarly done with the OSG exporter.