Hello! Tell me, please, what is the meaning of this parameter, is there when exporting to .obj, and when .fbx. How does it even work and why is it necessary?
Rhino uses Z as the UP direction, some 3D applications use Y. If you are going to export a Rhino model to those applications, you will have to enable Map Rhino Z to OBJ Y. The model will be rotated -90 degrees around the X axis (or you can say the Y and Z axes are rotated 90 degrees around the X axis) while exporting. So the model can be imported to those applications with the correct orientation.
And why do they use exactly Y? And in what programs?
Maya is Y-Up.
Why is there no generally accepted standard?
Lightwave is Y-Up too.
Read answers in the replies below.
Y is up typically for animation software like Maya and Lightwave because the dominant working plane for animation, film, games is in the side views or elevation, Z is depth of the scene. In Software like Rhino which is primarily used for schematic type design the dominant working plane especially for documentation is top view like plans, Z is height of the object.
Of course both types of fields use all views at some point but the coordinate systems of a 2D grid are understood in this medium.
Okay, now I understand
Solidworks is also Y-up, as are a couple of other MCAD programs AFAIK. It’s a matter of philosophy, Y-Up programs consider the Front view of an object the principal view, whereas Z-Up programs consider the Top (plan) view as the principal view.
If I may add a wee bit more confusion to the discussion. In ship design right hand orientation is used. Where the leading axis is the X axis which points to direction of the bow of the ship, Z+ is up.
However for hydrodynamic calculations Z+ is down (left-hand orientation) because it concerns itself with what is underwater and since the draft (or draught) increases downwards to save themselves writin “-” in front of every “z” member of an equation they decided to flip the axis.
It is all of mater of what they needed initially.
For engineering it is usually z-up. For graphical design it is actually Y-down because of the 2d screen starting the coordinate system in top-left. To the right is x+ and down is y+. You can still see this being used by any WinForms and their alternatives.
I think it’s also because of the programmers. If SW uses z-up (I sure if that is true) the the initial programmers of the software have graphical design background. If a software is z-up, the initial programmers have engineering background before deciding to become progranmers.