3.2 Route Planning and Coverage Strategy

Core Route Planning Principles

Walk Main Corridors First, Branch Into Rooms Second

Establish the spine of the floor plan before branching. The corridors give SLAM a continuous backbone to anchor everything against, and each later room entry becomes a loop closure relative to that backbone, correcting drift as you go. Branch first and the room-to-room relationships rely on weaker individual transitions.

Each Room Entry and Exit Is a Loop Closure

Enter a room, scan it completely, and leave through the same doorway. The system has now seen the corridor before and after the room, which lets it detect and correct any drift accumulated inside. Exiting through a different doorway loses this. Where a room has multiple doors, enter and exit through the same one.

Close the Final Loop, Then Stand Still

The most important loop closure of any session is the last one. It corrects drift across the whole session rather than one segment, and it is the one most often thrown away. Two things have to be true at once: you are back at a position you already scanned, and your viewing angle is within about 40 degrees of your original angle at that location. Returning to the start from the opposite direction satisfies the first and fails the second.

Getting back there is not the end of it. The device needs a few seconds of stationary observation at the recognised position to run the match and redistribute the correction back across the trajectory. Walking to the start point and pressing stop skips that.

• K2: return to the starting point, stand still for a full 10 seconds holding the device stable and facing the direction you originally faced, then stop recording in the app.
• L2 Pro: return to the starting point and hold the same posture and orientation for several seconds before stopping. The preview visibly tightens when the match lands.
• PortalCam: return to the vicinity of the starting point and stand still for several seconds before stopping.
• All devices: after pressing stop, wait for solid green before doing anything else. A fast green flash means the file is still being written, and the flash lasts longer on a larger scene. Cutting power during it can truncate or lose the project.

Movement Patterns Within Spaces

Inside rooms and open areas, the path determines coverage. Random movement leaves gaps; systematic patterns give multiple angles on every surface.

The Three-Pass Indoor Method

For interior spaces, three passes in a single continuous session produce far more complete coverage than one thorough pass. Each pass has a different job, and the third is the one people skip.

• Pass 1, wall perimeter loop. Walk slowly along the walls with the lens pointed at the opposite side of the room. Stay 0.5 to 1 m (1.6 to 3.3 ft) from the wall at 0.3 to 0.5 m/s (1.0 to 1.6 ft/s). This records the overall room structure and gives stable side-view overlap between frames. In a multi-room space, loop each room and pause longer at the doorways.
• Pass 2, grid traversal. Move into the middle of the room and cross it two or three times in each direction to form a grid, lens at eye level facing your direction of travel. This captures objects in the centre of the room and the depth relationships between them, and it is what rescues weak-texture areas like white walls and open floors by adding multi-angle constraint.
• Pass 3, ceiling and floor. Walk the same routes again with the lens angled up, then with it angled down, within the tilt limit for your device. This is the pass that fixes ceiling shapes, light fixtures, baseboards, floor material, and the underside of furniture.

Varying your carry height between passes adds a further axis of angular diversity: chest height on pass one, higher on pass two, lower on pass three. Keep the height consistent within a single pass so quality is even, and change gradually between them.

All three passes must be one continuous session. Stopping between passes creates artifacts at the joins. A three-pass scan takes roughly 2.5 to 3 times as long as a single walk-through, with a significant gain in 3DGS quality and a real gain in ceiling and floor completeness for point cloud work.

Long Corridors and Featureless Runs

Corridors drift faster than open spaces because repetitive walls offer fewer distinguishing features per unit of travel, so SLAM has less to compute position from.

Branching Frequency

• Corridors over 50 m (160 ft) without positioning: branch into at least one room and return before the far end. A straight out-and-back accumulates uncorrected drift.
• With RTK holding Fixed, corridor length stops being the constraint. What binds instead is how far you travel without a fix: keep any continuous unfixed stretch under 100 m (328 ft) on the L2 Pro and under 50 m (164 ft) on the K2. A corridor that never drops the fix is bounded by the coordinate stream regardless of its length. Branching is still worth doing.
• Any space counts as a branch. A brief detour into a closet, electrical room, or break room creates a loop closure that resets accumulated drift.

Side Shuffle in Narrow Corridors

For corridors under 2 m (6 ft) wide, the side shuffle keeps both walls in view and gives SLAM geometry a forward walk cannot. Budget about 50 percent more time for any corridor walked sideways.

Targets in Featureless Corridors

For long corridors with no distinguishing features, place high-contrast anchor targets along the run. Alpine practice is every 30 to 45 m (100 to 150 ft); adjust to how featureless the run actually is. Any flat, high-contrast, non-reflective marker works. These give SLAM explicit features to match when the surrounding geometry is uniform, and they need no surveyed coordinate to do that job. Attach surveyed coordinates in processing and the same target becomes a ground control point. See Module 4: Positioning.

Multi-Floor Coverage

Each floor is scanned in sequence, with stairwells providing geometric continuity between them.

Order of Floors

• Start at the ground floor and work up. It connects to the most exterior coordinate references, which anchors the floors above.
• Scan each floor as a continuous session from exiting the stairwell to re-entering it.
• Do not stop between floors. The stairwell is part of the session. Stopping creates separate sessions that must be joined with Map Fusion, which aligns less cleanly than a continuous scan.

Stairwells

See 3.3 Transitions. Stairwells take longer than their footprint suggests and are a high-failure transition. Plan time accordingly.

Elevators

The elevator car moves through space the scanner never sees, so SLAM loses track between floors.

• Do not scan inside elevators. Stop before entering, ride without scanning, start a new session on the next floor.
• Join sessions with Map Fusion. Each must share overlap geometry with its neighbors. Use the stairwell for at least one transition between any two floors to provide alignment data.
• Pick one canonical stairwell as the inter-floor connector when a building has several.

Session Length and the Continuous Session Principle

SLAM depends on continuous trajectory data, so a single session is always cleaner than two joined ones. But a session cannot be arbitrarily long, and the limits are much shorter than most operators expect.

The Numbers That Bind

• Plan 12 to 15 minutes per capture. The working target, with room for unexpected coverage.
• LixelStudio Map Fusion requires each capture under 20 minutes. A longer capture cannot be fused for point cloud output at all.
• LCC Studio capture guidance is 30 minutes or less per map.
• Workstation memory is the real ceiling. 64 GB reliably reconstructs about 30 minutes of capture and risks failure past 45. 128 GB reliably handles about 60 minutes and risks failure past 90.

Use One Continuous Session When

• Single-floor projects that fit inside the capture limits above.
• Multi-floor projects, one session per floor, joined at stairwells.

Break Into Multiple Sessions When

• The space exceeds the capture limits. Split into planned segments and join with Map Fusion.
• Floors are elevator-separated. Each floor is a session, joined by stairwell traversal or Map Fusion.
• Multi-day projects. Each day is a session. Plan day-to-day overlap for Map Fusion.
• Operator fatigue. Rest every 45 to 60 minutes. Past about 2 hours of continuous work a rested operator produces better data than pushing on.

For Map Fusion planning, see Module 5: Map Fusion Fundamentals.