Physical space limits the virtual travel range
Aliases: tracking volume · play area · room-scale walking
What it is
The living room is three metres square; the virtual gallery is thirty metres deep — walkable distance is clipped by the rug edge first. Room-scale means that when natural walking is the locomotion, virtual reach is capped by the physical tracking volume, not by how large the scene is drawn. Content can be bigger. Feet only reach the patch that walls, furniture, and cameras can see.
This is a locomotion budget, not how a safety cue is drawn. Whether the cue appears is a different design.
Why it happens
Six-degree-of-freedom tracking maps head and hand positions onto a virtual origin. Each physical step translates the virtual camera one step; the match is literal. The boundary of the tracking volume — walls, table legs, lighthouse field, the effective radius of inside-out tracking — is the farthest that match can be maintained. Beyond it, either a real object is hit or tracking is lost, and gait can no longer supply virtual translation.
Content scale and physical scale therefore have to be booked separately. A scene smaller than the tracking volume can be walked entirely; a larger one must introduce non-walking locomotion, or the far door is unreachable. Seated and standing-in-place shrink the volume to an arm radius plus half a step, and the room-scale budget is nearly zero. Furniture carves the volume into an irregular polygon; a nominal four-metre room may leave only a walkable corridor.
Studying it
Measure the actually walkable polygon before talking about content. A typical contrast is the same “walk to the marker” task in an empty room, a furnished room, and standing-in-place, recording arrival rate, detour paths, and when people switch to teleport or stick. Tracking volume (clear area, obstacles, sit/stand) is the manipulation; completion, extra-locomotion invocations, and tracking-loss counts are the observations.
Self-report of “my home is large” is unreliable. Floor plans or the headset’s drawn play area and the area people will actually walk often differ by a strip — the ring next to the wall is left blank spontaneously.
Where it stops holding
Redirected walking, teleport, and stick sliding are substitutions for when room-scale is insufficient; they do not change the fact that walking range is physically capped. Outside-in volume moves with lights and base-station placement, so the same content is two products in a lab hall and a bedroom. Under optical AR people see the real wall; the limit is collision risk and social space, not only tracking loss. An infinite floor that assumes a hall fails in most homes as unreachability, not as sickness.
Applying it
- Design the segment that must be done on foot to the target venue’s walkable area. Distances beyond that need non-walking locomotion. Do not assume the living room is the gallery.
- In setup, show people their play-area polygon and mark levels that “need walking,” with a seated alternative.
- Do not put critical path on a straight-line distance longer than a common household clear patch (roughly two to three metres).
- How to check: walk the main path once in a cleared living-room scale and once in the same room with a table left in. If the latter cannot reach the marker except by hitting furniture, content scale has exceeded the physical budget.