Body-anchored interfaces travel with the person

What it is

Walk from one end of the room to the other. The menu at the hip is still where that hand can reach it. A body-anchored interface travels with the person: input targets are stored on the torso, so translating the body takes the whole reachable kit along. Nobody has to walk back to a patch of floor to retrieve their own tools.

Travel here is translation, not turning. Whether a target is still in front of the belly after a ninety-degree yaw is the next leaf’s reference-frame question. This one only guarantees: walk, and the tools are still on you.

Why it happens

An input target is stored in some coordinate frame. Stored on the floor, a walk changes the target–hand relation: a button that sat a palm in front of the belly stays put and becomes a point behind or beside, out of reach. Stored on the torso, the relation is a constant: ten metres later the button is still a palm in front of the belly. The hand’s planner can reuse the same arrival; it does not have to re-sight at every new stance.

This is a tool worn on the body, not a tool left on a table. A hammer that travels with the hand can strike at the next work point at once; a hammer left on the last table forces a choice between continuing and going back. If high-frequency spatial entries stay on the departure floor, movement splits the person from their own kit: they either stop moving or drop the kit. Body-anchoring cancels that choice.

Studying it

Give a set of entries, compare stored on the torso with stored on the floor at the start, and have people walk to another mark mid-task and continue.

Independent variables: target stored on torso versus in the room, distance walked, whether looking back is allowed during the walk. Dependent variables: time to first reach of the entry at the new stance, trips back to fetch the tool, switches to a substitute entry, rate at which movement is abandoned.

The first hit at the new stance is the observation that matters. Torso storage should barely add time; floor storage should force a look-back or a distant substitute. Do not measure “is it usable” only while standing still — travelling with the person is a property that appears only once people walk.

Where it stops holding

When the work object itself lives in the room (a drawing on the wall, a model on a table), an entry that also rides the body takes the tool and leaves the object; the two split. Travel-with-the-person is then the wrong move. When several people must jointly point at the same control, the control has to stay in the room so two bodies can aim at it; parked on one person it is a moving target for the other. In a seated session with almost no translation, the benefit of travelling is near zero and the cost (another torso origin to track) remains. Unstable torso tracking, a hip origin that sways while walking, will make the riding interface jitter, and people will prefer it left on the floor.

Applying it

• Store system menus, personal tool strips, and status that serves only this user on the torso, so they remain reachable after a walk.
• Objects that belong to the room (a shared board, parts on a table) should not follow the person. What travels is the person’s kit, not the room’s furniture.
• Do not hide riding entries at the start of a walk “until you stand still” — that is exactly when people need to confirm the tools are still there.
• How to check: mid-task, name a new stance two metres away and forbid returning to the origin. If the entry is still a one-shot reach at the new stance, travel holds. If people reach toward the old floor, or ask “where is my menu,” the coordinates are still in the room.

Related

• Same group: N2.07.1 The body supplies a location reference that does not need vision · N2.07.3 Choice of reference frame decides what happens after a turn · N2.07.4 The head is the worst body site for an anchor · N2.07.5 A waist anchor is more stable than a shoulder anchor · N2.07.6 A wrist anchor brings the interface into view at the cost of raising the arm · N2.07.7 Anchor distance must scale with body size, not a fixed length
• Nearby: N3.01 Locking Modes · N3.08 World-locked, Body-locked, and Head-locked
• Search terms: body-anchored interface · ego-moving tools · torso-relative UI