I played around with 3D shapes and I noticed that the way the 3D space is oriented is not the one I would have expected.
The picture below represent:
- the x axis in red
- the y axis in green
- the z axis in blue
- the dots indicates the positive sides
As you can see, the world is using the “left hand” convention. I was expected the x axis to point toward the right side to fit the “right hand” convention. Math and Physic both used the latest.
Is there a particular reason why it was setup like this?
For a 2D sketch, which most people are usually going to start with, the system is orientated so that the top left is (0,0), X+ is to the right, and Y+ is down - similar to how people write on paper. I believe the lore is that this was an attempt to make it easier for new programmers to understand.
Adding the third dimension, Z+ is in, so things with large Z seen father away, making Z the distance from the viewer. Again, this is easy for people to understand.
EDIT: Ignore this bit.
What results is a left hand system. Expert users are not alarmed, however, as a simple call to scale(-1,1,1) can resolve this for them.
… At least that’s what I was told…
That was also my thought at the beginning but having a left hand system make the Z direction going from the screen to the viewer (keeping x to the right and y to the bottom) making it again counter intuitive IMHO…
No strong opinion on the Z-axis, but the 2D and 3D systems both have x,y axis that are logically consistent with each other – so you get similar behavior if you change from P2D to P3D rendering.
The decision to use piece-of-paper orientation was originally in the context of 2D, I believe – for some in 2D it can also be surprising that the origin is in the upper left, not the lower left. Thankfully 2D and 3D are consistent with each other. I think that is the most important thing of all.