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Yes, I *still* have to look this up sometimes because I've used and made so many engines and tools that I don't know which hand is which and which way is up half the time ;) Gotta laugh at UE in the corner on its own there.
Ogre was right-handed (aka the canonical way if like me you learned from the Red Book) but had no concept of "up", technically. It could be whatever you wanted 
@sinbad I queried the search engines for a while and never managed to find out why. Why would UE choose this coordinate system, breaking everyone's expectations about where the axes should be, all three in my case.
@kr4ft3r I can understand Z up, it makes 2D only calculations more sensible (truncate 3 items to 2, instead of having to swizzle XYZ to XZ like in Unity. Left hand coordinates are usually because people want positive coords to go into the screen not behind you
@sinbad That's all fine but I can't grasp the reason behind X forward, which also implies that X would be vertical in 2D, idk about real mathematicians but this is the opposite from what most coders expect.
@kr4ft3r when +Z is up and left handed, +X being forward makes +Y the right vector. People like positive bases
@sinbad Well thanks, that makes sense. Still doesn't explan why UE chose to be sitting alone over there, could it be some programmer's decades old arbitrary decision or was there a proper reason, I guess former and can leave it at that.
@kr4ft3r bear in mind this was decided by Tim Sweeny in 1998 before most of the others were even made, so you could say they all just decided to do something else
@kr4ft3r also all the choices are arbitrary, none of them are right or wrong - most math texts tend to be right-handed but even MS threw that out the window because they wanted increasing depth to be +Z
@sinbad @kr4ft3r in a WYSIWYG editor, I'll agree. But in code-only editors, Y up is the only way 3D makes sense to me. You're looking at a screen of X,Y units and adding a depth to it. You even have Z buffering to log the depth of a thing the further into the screen it goes. I can't fathom why anybody would then think it best to flip that organic axis over and have Z pointing upwards. 
