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UE4 coordinate system confusing

I'm trying to better understand the UE4 coordinate system in the context of importing models, but I still can't make total sense of it. So far, this is what I have:

  • UE4 is a left-handed coordinate system

  • +Z is up

  • +X is the forward axis

When I import a model into my content, the thumbnail in the model is facing forwards:

alt text

Yet when I drag the model into the scene, this is the result:

alt text

Why is the model 90 degrees on the z-axis from the correct forward axis? The asset thumbnail suggests that it is facing the correct direction (and indeed, if I rotate the model 90 degrees on the z-axis, prior to import, the asset thumbnail is facing the wrong way), but the drag-and-dropped model isn't facing the correct direction. It seems like the "forward-axis" is not actually forward? Why does the model's orientation disagree with the default camera orientation? I am struggling to come up with an easy way to think about these coordinate system rules.

Product Version: UE 4.22
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asked May 28 '19 at 01:06 AM in Using UE4

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amoffat
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I'll go out on a limb and say it's the thumbnail that is offset - prettified. You can enable thumb edit mode in the bottom right ViewOptions - and then dragging the thumb updates its rotation. It's clunky, you've been warned.

edited: removed some nonsense

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answered May 28 '19 at 06:47 AM

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Everynone
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avatar image amoffat May 28 '19 at 04:51 PM

My model's X axis aligns correctly with the world's X axis, true, but the issue is that my model's X axis is not what I would consider "forward", since it is pointing down my model's left arm. The way I imagine it, my model's forward axis should be pointing out of my model's back, since I am looking at my model from the front in my modelling software, down the forward axis. The only way I would consider the forward axis being down the left arm is if UE4 coordinate system is thought of as a side-scroller, then it makes perfect sense.

I guess my issue is more about why the thumbnail disagrees with the scene. The thumbnail appears to be looking down -Y for the capture, which doesn't make sense to me. I could adjust the thumbnails like you suggest, but I pulled up some UE4 sample content projects, and all of their static and skeletal meshes are all suffering from the same issue: the thumbnail is correct, but the model's forward axis is down the model's left arm.

avatar image Everynone May 29 '19 at 09:27 PM

Sorry about the confusion, my bad. Your model is facing Y for some reason. I see what you mean now, what are you exporting it from? Some software has the coordinates system backwards, like Maya from what I heard (not a Maya guy myself). Most exporters allow you to fix up the coord system, though.

I guess my issue is more about why the thumbnail disagrees with the scene.

I've been staring at the thumbnails for such a long time that I no longer notice that I guess.

edit: edited my post a bit to avoid confusion

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