I find that trying to make sense of terms like “to the left” tricky when we can rotate the directional cube any way we want. For example, in my drawing for “Y-up, left handed”, the red X axis is pointed leftwards. However, we could rotate the unit vector cube so that the X axis is pointed right, and the Y axis is pointing up (i.e. the orientation we’re most familiar with for 2D graphs). The Z axis would then be pointing away from us, into the plane of the paper/screen.
In contrast, if we oriented the Y-up right-handed cube in the same way, then the Z axis would be oriented as if to come out of the plane of the screen/page, towards us.
These distinctions only matter when we add a third dimension, so the left or right handedness is basically a question of "when we add the third axis to a 2D square made by the other two axes, does the third axis come towards us or away from us? I apologise if this hasn’t made things any clearer — I am able to make things make sense by imagining the rotations in my head, but not everyone is able to visualise them like that.
From the chart I would guess that in Y-up right-hand positive X is to the right. You look at the palm of your hand.
That way when you develop a 2d platformer you would use a standard XY coordinate system. Switching to 3d would logically add the z axis as depth and not height. A movie is usually shot that way as well.
Of course that analogy breaks down as soon as your base-game is top down. Like a city planer or so.
Anyways, with standards it’s often best to just go with what most others do. So kudos to Unreal for not being stubborn.
Okay, am I understanding this correctly? In Y-up right-hand, positive X is “to the left”?
No, the x-axis is usually the only consistent one (it increases from left to right). With right handed coordinate systems you can have Z going into the screen (Y-down) or Z coming out of the screen (Y-up)
You’re right that I didn’t sufficiently consider the “was” in that sentence. Perhaps there’s something I’m missing though, because I haven’t seen anything that would suggest X is left. When I put my right hand in the position indicated in the OP, my index finger (Y) points upwards, with my thumb (X) pointing right, making an L shape. My middle finger (z) comes out towards me.
However, most of my experience with coordinate systems is with abstract, mathsy stuff, and I don’t have much experience with any of these softwares; there may be something obvious that I’m missing.
Okay, am I understanding this correctly? In Y-up right-hand, positive X is “to the left”?
I personally think that right-hand Z-up makes the most sense, but it makes sense to move to where most of the industry is going.
Z is depth. Why should it ever be up? Honest question.
It depends if you view the X-Y plane as the camera/viewport/screen or the ground. If X-Y is the ground, then Z is either up or down.
For cameras, the convention is Z depth but right handed:
I don’t think that’s correct. Here’s a drawing I did when trying to get my head around this.
drawing
I find that trying to make sense of terms like “to the left” tricky when we can rotate the directional cube any way we want. For example, in my drawing for “Y-up, left handed”, the red X axis is pointed leftwards. However, we could rotate the unit vector cube so that the X axis is pointed right, and the Y axis is pointing up (i.e. the orientation we’re most familiar with for 2D graphs). The Z axis would then be pointing away from us, into the plane of the paper/screen.
In contrast, if we oriented the Y-up right-handed cube in the same way, then the Z axis would be oriented as if to come out of the plane of the screen/page, towards us.
These distinctions only matter when we add a third dimension, so the left or right handedness is basically a question of "when we add the third axis to a 2D square made by the other two axes, does the third axis come towards us or away from us? I apologise if this hasn’t made things any clearer — I am able to make things make sense by imagining the rotations in my head, but not everyone is able to visualise them like that.
From the chart I would guess that in Y-up right-hand positive X is to the right. You look at the palm of your hand.
That way when you develop a 2d platformer you would use a standard XY coordinate system. Switching to 3d would logically add the z axis as depth and not height. A movie is usually shot that way as well.
Of course that analogy breaks down as soon as your base-game is top down. Like a city planer or so.
Anyways, with standards it’s often best to just go with what most others do. So kudos to Unreal for not being stubborn.
He references “Left-Up-Forward”, so X is Left, Z is into the screen.
2D is not a consideration, even if it’d be logical. (That’s where Left-handed Right-Up-Forward grows out of.)
No, the x-axis is usually the only consistent one (it increases from left to right). With right handed coordinate systems you can have Z going into the screen (Y-down) or Z coming out of the screen (Y-up)
That makes more sense. Simple explanation of my error. Thank you.
You are wrong, @egerlach@lemmy.ca was correct:
Source: https://forums.unrealengine.com/t/we-re-moving-to-the-left-up-forward-luf-coordinate-system/2540901
I don’t think that’s right. The post that you linked to includes this link, which includes this snippet:
I don’t follow why that means I’m wrong.
“Was” here refers to their old Z-Up, left-handed coordinates, where X was forward, Y was right, and Z was up.
You’re right that I didn’t sufficiently consider the “was” in that sentence. Perhaps there’s something I’m missing though, because I haven’t seen anything that would suggest X is left. When I put my right hand in the position indicated in the OP, my index finger (Y) points upwards, with my thumb (X) pointing right, making an L shape. My middle finger (z) comes out towards me.
However, most of my experience with coordinate systems is with abstract, mathsy stuff, and I don’t have much experience with any of these softwares; there may be something obvious that I’m missing.
You can spin your hand 180° around Y (index / up). Then Z (middle) points away from you, “forward”. And X (thumb) will point left.
Thus the “Left-Up-Forward” + Right-handed.