Hi Burr - OBJ files do not actually have a method inside of them to label which direction is supposed to be "up".

So when you export from MoI as "Y-up", it is talking purely about how your objects are going to be oriented in the resulting file, the coordinate system labels (what directions you see labeled as x, y, and z) in the receiving application are not going to be changed when reading in the OBJ file.

But some programs expect to have OBJ data with Y pointing up and others with Z pointing up, so that setting allows you to adapt MoI's OBJ export to suit the target application so that you don't have to rotate it after you import it.

- Michael