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Fredrum
Up and Coming
November 2, 2016

Where does the Unreal HMD tracked position sit in real world?


I'm looking for some documentation that describes where in the real world the tracked HMD position returned by Unreal actually sits.

I'll assume that it is of course in the centre left to right,
but where is that point located relative to, say, the CV1 headsets exterior front surface? Ie how far back from the front surface?

Is this described somewhere?

Cheers
Fred





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2 replies

vrdaveb
Inspiring
November 3, 2016
The HMD pose is reported relative to a "tracking origin", which can be at one of two places, depending on your HeadMountedDisplay settings:

Eye Level - The initial pose of the HMD when the camera activates.
Floor Level - The origin set by the user during calibration. This is typically near the center of their playable area. Unlike eye-level, the floor-level origin's position is on the floor, at Y = 0.

When you recenter the tracking origin, the behavior is different for eye and floor level. Eye level moves the origin's position (X, Y, and Z) and the yaw (Y rotation) to match the current head pose. Pitch and roll (X and Z rotation) are not modified because that would make the app's virtual horizon mismatch the real-world horizon, disorienting the user. Floor level moves the origin's X and Z position, but leaves the Y position alone to keep it consistent with the real-world floor. Rotation is handled the same way as eye level. See https://developer3.oculus.com/documentation/intro-vr/latest/concepts/bp_app_tracking for more detail.
FredrumAuthor
Up and Coming
November 8, 2016

Hi Dave,  and thanks a lot for the elaboration!
I am rebuilding my full body character rigs somewhat and especially the HMD driven neck and spine. Hopefully this will help me doing things like an inverse neck model more precisely. I was thinking that I might need the exact rotation pivot location relative to the HMD to do that but maybe thats deducible from your info or maybe.
Thanks I'll let you know how I get on.

Cheers
Fred
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