Top one is incorrect. Z needs to point outwards.

The top one is wrong because it violates the right hand rule.

No, there are 3 actually:

Z is elevation. Any real world application, z goes up down. 3D applications SHOULD use it for elevation. I despise that many do not. It's so fucking confusing. 2D, sure y go brrr. But once that 3rd dimension is added, y needs to take several seats and quit trying to take on dimensions it doesn't have any right to.

I legit had no idea anybody actually used the upper system until now. I had to read the comments just to see whether the upper system was just some sort of joke. I am horrified.

y-up ftw

It's easier when writing 3d renderers cause the x and y coordinates of the 3d points eventually become the x and y coordinates of the 2d points on screen and it's easier to keep track of

X is up, there now no one is happy.

I'll leave this here for context (bottom right is the only sane one)

One of my friends and I used to always have this debate because of our different backgrounds. I got used to +Y being up because of doing physics for several years and seeing side-on diagrams that needed to account for gravity. My friend has a background in geology, so he's used to top-down surveying maps where +Z is up. It all depends on your perspective.

But my way is right. We need to have standards, people.

Z is depth, full stop, and I have my fists raised, Queensbury-style, to anyone who contends otherwise.

Minecraft

Above and below the page/plane is the z-axis.

But some people "hold" the page up in front of them, or down on the table.

Neither of these are right. X is forward, Y is to the right and Z is down.

Source: https://iansguides.com/tutorials/aircraft-coordinate-system-and-anatomy/

Thanks to 3D printing Z is firmly “up” in my brain even if the modeler I use does it differently.

ah yes the correct way and the Minecraft way

Weird didn't everyone learn XY on paper on a desk first? All they did was add z axis to that original concept for elevation which gives us the bottom image.

Top image is like if I held paper straight parallel to my face.

In 2D Y is up, in 3D Z is up.
X is always red🤷‍♂️

Right handed and left handed? (Top image doesn't follow right hand rule, Z should point towards camera)

Z is always depth. Both are correct but define different perspectives. Top is looking across the landscape from an arbitrary floating perspective, bottom is looking down with anchored mapping to the surface.

Yeah... As a Blender 3D artist, Z axis has been baked into my brain as the up/down axis.

<i,j,k> vector master race.

In a 2D game Y is up. Going from 2D to 3D would make sense to add another dimension forward to account for depth.

However if you start with a map of a 3D surface then North is Y and East is X you'd add Z to account for elevation like everybody making maps would.

I guess it depends on how you look at it.

No, just no. x is the variable for depth, y is the variable for width, and z is height. I learned that from multivariable calculus, no other convention is better.

Fuck you for showing me this, I'm now going to gauge my eyes out.

In my brain Z is Up, Z is Height. In my job I have to deal with both all the time which is quite annoying.

This reminds me of the time when I was in an industry robotics, there were a right hand rule where Z was your thumb up and X and Y your index and middle fingers. So I think the second one is the right, but it should have been drawn other way round.

Technically, there's a lot more options. Any axis can have any name. The reason why these two main systems exist is because of 2D coordinates.

A 2D coordinate system can either be viewed top-down (piece of paper on a table) or from the front (pixels on a screen). So while X stays the same in both of these options (and thus isn't contested in 3D coordinates), Y is either up (on a screen) or ahead (on paper), and Z then gets whatever axis is left over.

Basically: Platformer vs Top-Down, which would you choose if you were forced to make/play a game 2D only

I am the latter, because if I draw a X-Y plane and lay it on the ground, it aligns with that XYZ reference frame.