When the anchor is recomputed—at engagement or by continuous following—affects consistency

What it is

Even after deciding whether the anchor nails to the device or the body, one still has to decide when to recompute the box pose: freeze it on the engagement frame, or follow continuously every frame. A body anchor locked at engagement becomes, for that session, a fixed patch relative to the chest of that moment; if the chest then shifts, the valid hand region does not. Continuous following updates every frame and the box sticks to the body. The two timings give two consistencies: locked to the body at session start, or to the body now.

Why it happens

Lock-on-engage stores the root pose as a session origin; later containment is relative to that snapshot. During the action the box does not jitter with breathing and weight shifts, so a continuous drag has a stable frame. The cost is that after a half-step mid-session, proprioceptive “in front of me” has moved and the box still sits at the old front, so the hand reaches into empty air. Continuous following writes a new root every frame, so “in front” always faces the current chest, but micro-motion of the shoulders jitters the origin and the cursor or hit region shakes. A compromise is low-rate following (say 2 Hz) or following only in the horizontal plane, ignoring vertical heave. Timing cannot be inferred from “we used a body anchor”; it has to be specified.

Studying it

Under one body anchor, compare three timings: lock on engage, per-frame follow, low-pass follow. Tasks: stay put after engage and adjust continuously; sidestep after engage and then adjust. Dependent measures are jitter of the adjustment curve, hit rate after the sidestep, and “is the box still in front of me” reports. Use breathing and deliberate shoulder sway as disturbances. Do not measure only the first hit at engagement; timing differences show up in the seconds after.

Where it stops holding

When a device anchor is nailed to an immobile screen, recomputation timing is almost meaningless—the screen does not walk. In full-body dance or sport, lock-on-engage expires at the first step and following is required. Fine mid-air drawing wants a stable frame; per-frame following writes body noise into the stroke. When the root is lost and then recovered, a following policy teleports the box; a lock policy may point at empty air where the person no longer is. Recovery policy has to be designed with timing.

Applying it

• Configure lock-on-engage / continuous follow / low-pass follow explicitly, and in debug draw a ghost of the box to show whether it moved during the session.
• Use lock-on-engage or a strong low-pass for precise continuous work; use following for commands that must work while walking, and suppress vertical jitter in the breathing band while following is on.
• Accept on two recordings: stand and drag for 10 s, inspect curve noise; halfway through, sidestep half a step, inspect whether it still hits. The two recordings are the two timings’ costs.

Related

• Same group: C4.21.1 The coordinate anchor decides whether the volume is device-fixed or relocates with the body · C4.21.2 A device-fixed anchor requires the user to remember and return to the same physical location · C4.21.3 A body-anchored volume keeps the operating experience consistent after the user moves
• Adjacent: C4.15 Conditions for entering engagement · C4.13 Full-body pose and skeleton tracking
• Search: anchor lock · continuous following · recompute on engage