Unreal Engine to move to using Y-up

Because a flat surface is an x-y plane. The ground is a "flat" surface, and so the z dimension is height.

For me, that's the only way that makes sense. But I program robots for a living, so I'm used to dealing with coordinate systems where the flat reference is the ground. Programmers seem to be using the screen as the flat reference. If I were building a game world, I'd probably use z-up convention.

Programmers seem to be using the screen as the flat reference.

In screen coordinates, the origin is the top left corner of the screen, and the Y-axis increases towards the bottom of the screen. So Y still isn't "up"
- His point is that's where it comes from. In most 3D software as seen in the chart, the XY plane is paralel to the screen, just that Y is up instead of down like in 2D, cut that would be insane if it was like that.
I'm old enough that I also was exposed to Y-down, and that's still my default.
Yeah, it depends on whether you expect the 2D view to be on the floor or on the wall. If it's on the floor, Z is up. If it's on the wall, Z is forwards & backwards (depth). Personally I think it being on the wall makes way more sense since we already expect from 2D view that Y is up and down, it feels weird to shift it to forwards & backwards when switching to 3D.

Z-up right handed makes the most sense

Every kid learning math has to at the very least learn X and Y coordinates for graphs. That's the reason I think Y is the natural up, it just makes more sense to be in line with what everyone already know instead of flipping it around.
- You looked down at the math book on your desk that showed the X-Y graph on the page, and the Y axis extended forward, away from you. Z was "up".
  
  I always thought about it like this. Put your fancy page with X-Y coordinates on the ground. Add a new dimension perpendicular to the ground. This is the Z-axis, it goes up.
  
  I have to agree as well, the ground is the most natural plane to be x-y.
  
  But in those cases, isn't positive Z going "away" from you ? I.e. Into the ground ?
  
  And in math classes this has always been described to me as adding "depth".
  
  I could see that being totally valid after thinking about it for a second!
  
  I imagine it as a new dimension growing “up” out of the X/Y plane (as burrowing into the ground would be going into “occupied” space, it’s forbidden). But “depth” does make that make more sense.
- I disagree – I think Z up is much more natural in this sense. X,Y is a plane, and it's much more natural to think of a plane as being horizontal, especially in a 3D environment with a ground plane. Z is the third dimension, perpendicular to that plane. Think about it this way, doesn't it makes way more sense to have a map with X,Y coordinates rather than X, Z coordinates?
  
  Fully agree with you.
  
  Y-up doesn't make sense in gamedevelopment at all. All those changes, because some dinosaurs of the past decided that Z is their screen depth.
  
  And what should we do with all previously released games? Refactor all vectors?
  
  I feel like whiteboards have gone extinct or something. All of my math lectures from grade school to uni took place on a y-up surface. I can appreciate that there are multiple ways to skin a cat, but I feel like people just argue what's most convenient for their preference in this kind of situation.
  
  Yeah you'd draw it on a vertical whiteboard, but in physics and math (or at least all the classes I had), you'd always draw a coordinate system with Z going up. I can understand why it would make sense for you to look at XY being a vertical plane, but I feel like it just makes more sense for XY to be the ground.
  
  Also, convenience wise, especially in e.g. game dev, for 90% of use cases it's way more convenient for the first two coordinates to be the ground position and the last coordinate be the height. Whenever you're thinking of the coordinates of something, you'd probably first think about its ground position and then its height, in which case it's much simpler if those ground coords are at the start, instead of at the beginning and end of a vector.
- Imagine you’re drawing a level or a city or a landscape. Wouldn’t you want to work in X and Y for this? Precisely because you’ve learned the X and Y coordinates in school. Then you add Z as the height.
  
  Yeah, for cases like maps it works, but most everyone that draws don't do bird eye view drawings. I'm just saying, I think it's more natural for people to draw scenes on 2D planes, and converting that to 3D Z as "depth" makes more sense. Although all the reasons I've heard for Z as height also makes sense to me now.
This is how engineers are trained for physics calculations.

Cartesian geometry makes z up 🤷🏻‍♀️