Question Does Physics2D.CircleCast have an orientation?

You cannot cast along the Z axis, it's a 2D physics system. Checking if something is at a specific position in 2D space, even if you filter by Z depth is just an overlap test i.e. Physics2D.OverlapCircle etc. There's no cast/sweep through Z.

All 2D lives on the XY plane.

 

It's just a convenient filtering option for results where you can ask that only colliders where the respective Transform position Z is within a range. Know that the physics system knows nothing about Transforms or Z position because it's obviously a 2D physics engine. We just add that utility to fitler the results coming from the physics system for you.

All the queries also use the ContactFilter2D which has all these filtering options. It's a good place to see those options.

In the end, 2D physics allows 2D spatial queries on the XY plane. It only has 3 degrees of freedom which are X and Y position and Z rotation. Nothing else exists in the actual physics system. Anything beyond that is just utility we add and in the case of Z position, because Unity is inherently a 3D engine, we provide that post filter option even if the physics system knows nothing about it.

I will say though that the API does describe this. It says:

• MinDepth - Only include objects with a Z coordinate (depth) greater than or equal to this value.
• maxDepth - Only include objects with a Z coordinate (depth) less than or equal to this value.

So specify the minimum Z and maximum Z depth and everything including and within those limits are returned, everything else is filtered out.