What is "zero extent traces"

I found something I didn’t know while reading unreal documentation.
“zero extent traces” what is this?
No matter how hard I looked, there was no information about this.

Below is the full text that I found.

  • Currently, spheres are only used for rigid-body collision and Unreal’s zero-extent traces (e.g. weapons), not non-zero extent traces (e.g. Player movement). Also, spheres and boxes do not work if the StaticMesh is non-uniformly scaled. In general you probably want to create UCX primitives.

zero extent traces = line trace
non-zero extent = volume trace (box / sphere)

the extent refers to XYZ volume, you can often see it described with a vector:

In this case, it’s half the extent.


[…]spheres are only used for rigid-body collision and Unreal’s zero-extent traces

I find the very last bit somewhat confusing, perhaps it’s the wording. Spheres are used for line tracing! Sure! But that’d make the method non-zero extent by definition.

Perhaps my understanding of the whole thing is incomplete.

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thanks for you
That’s a great answer.
Of course, I’m still confused, but to sum up, the sphere is by definition “non-zero extent” and trace the line, right?

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Yup.

I guess you can sphere trace with 0 radius and still get results.

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