LiDAR works by timing light that bounces back. That is a wonderfully direct way to measure a wall, and it has a predictable failure mode: surfaces that send the light somewhere else.
The four troublemakers
- Mirrors — reflect the beam and report the depth of the reflected room. A large bathroom or closet mirror can read as a doorway into empty space.
- Window glass — often passes light straight through, so the scan sees the yard. Scanstead treats detected windows as openings in the wall, which is usually what you want, but a floor-to-ceiling slider can confuse the wall line.
- Glossy dark surfaces — black granite, a glass table, a wet floor. Dark absorbs, gloss reflects, and the combination returns very little.
- Open stairwells and double-height voids — not an optical problem, just nothing to hit within range.
What to do about it
The fix is almost always the same: give the scan the wall, not the mirror. Stand so the mirror is at an angle to you rather than straight ahead, keep a bit of distance, and make sure you sweep the wall surface around the mirror clearly. The wall plane is what the room model is built from, and a well-seen wall survives a confused patch in the middle of it.
For a wall of glass, scan the adjacent walls carefully and let the geometry close the room. For dark gloss, scan it from a shallower angle and get closer.
Check and move on
After each room, glance at the plan. A wall that bows, a room that has grown a phantom alcove, or a corner that will not close is the signature of a reflective surface. Rescanning one room takes two minutes.
Do not overthink it
Most houses have one or two mirrors and a slider. Thirty seconds of awareness per room is the entire cost.
The sensor is honest about what it sees. It is just not always looking at what you think it is.