Scan Stairs and Corridors - NavVis MLX

Introduction

Use this guide when your scan path runs through corridors, landings, and staircases, areas where feature-poor geometry and foot traffic commonly cause SLAM errors. You'll need open access to the full route at low foot traffic times.

General concepts 

Scan in both directions

• Scan corridors and stairs in both directions to support loop closure and ensure complete coverage.

• If the SLAM indicator turns yellow, turn the device so that the laser scanner can detect more features. Try to avoid the SLAM indicator from being yellow for extended distances.

Before attempting to scan a corridor, open all available doors. If the corridor has limited features, place additional objects, such as the device’s transportation box. 

1. Start in an area with many features

1. Start in a lobby, junction, or larger room.

2. Turn the device sideways (horizontal) and rotate 360° to capture key details for the laser scanner, including both corridor directions, nearby doors, ceiling, and floor.

2. Walk the corridor

1. Walk along the center line so both walls stay visible to the laser scanner.

2. With the device in the harness, walk slightly sideways (about 30–45°) to widen what is visible to laser scanner along the corridor. This allows the device to detect windows, door frames, and other corridor features, stabilizing SLAM.

3. Keep at least 50 cm from each wall.

4. If a corridor is narrower than 1 m and has few features (plain walls, no doors, no signs), SLAM-based errors are more likely.

3. Keep a steady pace

1. Walk at a steady, moderate pace.

2. Avoid sudden stops and sharp turns.

4. Scan in both directions

• Scan corridors in both directions to support loop closure and ensure complete coverage. Use one of these options:

  • Walk the corridor out and return, or

  • Walk it once, continue scanning beyond it, then return through the same corridor.

  • When you return, cross your earlier path at clear junctions to support loop closure.

  Note: Avoid scanning when there are moving objects or people in the corridor. If someone walks past while you are scanning, turn so the laser scanners face away from the movement.

Stairs

On stairs, watch overhead clearance and move slower than on flat floors. With the device in the harness, scan the staircase both up and down in the same dataset. This improves quality and reduces vertical mismatch in the point cloud. 

1. Capture context at the stairs

1. Start on a landing or in a corridor near the stairs.

2. Slowly turn the device sideways (so it’s horizontal) and rotate 360° so the landing, stair opening, nearby walls, and ceiling are visible to the laser scanner.

2. Scan going down

1. Focus on footing.

2. Keep one hand ready for the handrail.

3. Walk slowly and avoid quick turns, especially on narrow stairs.

4. At each landing, turn the device sideways in a sweeping motion so that it captures as much geometry as possible and detects the connection to the corridor (or next flight).

5. Capture panoramas at the bottom, middle, and top of the staircase.

3. Scan going up

1. Face the direction of travel.

2. Take short, even steps.

3. Move slowly and avoid sudden direction changes.

4. At each landing, turn the device sideways in a sweeping motion so that it captures as much geometry as possible and detects the connection to the corridor (or next flight).

5. Capture panoramas at the bottom, middle, and top of the staircase.

4. Scan complex stair shapes

Use extra care on L-shaped, U-shaped, and spiral staircases.

• Treat each flight as a short segment.

• On every landing, slow down and ensure the full landing area is visible to the laser scanners.

• For long staircases stop in middle. Remove the device from the harness and tilt the device and perform a sweeping motion, then return the device to the harness and continue.

• On spiral stairs, move especially slowly and keep a consistent distance from the center. Focus the laser scanner on the steps of the staircase, so it can detect the changing geometry as it curves around.

• Keep the inner and outer railings (and any central column) visible to the laser scanner.

5. Choose a safe stopping point

End the scan on a landing or in a corridor, not mid-stair, unless you must stop there for safety.

On-Site Quality Checks

If there are still areas of the scan area not covered, tilt the device exposing the area to the laser scanner.

Always monitor the SLAM quality while scanning and check the Quality Map.

Knowledge base: For detailed information refer to Quality Map Checklist

Post-Processing Quality Checks

Use NavVis IVION Processing to review the Quality Report for the dataset.

1. Check continuity

• Confirm corridor walls are straight and parallel, without sudden bends or twists.

• Confirm repeated features (for example, door frames) align consistently along the corridor.

• Confirm each set of stairs connects cleanly to the landing, and each landing connects to the correct corridor.

• Look for inaccuracies of the height of the steps, duplicate (“ghost”) surfaces, or sideways skewing or offsets.

• If you have a floor plan, spot-check that key junctions and stair connections match expected positions.

• In the Quality Report, check SLAM quality along the trajectory, especially in long corridors and stair sections. Compare with control points or reference measurements when available.

2. Check alignment with neighboring datasets

Verify that the dataset aligns well with neighboring datasets. Alignment should be accurate if scanning and processing were done correctly.

3. Plan a targeted rescan (if needed)

Plan a short follow-up scan that focuses on the affected junctions, landings, or stair sections. During this re-scan, move slowly and use clear connections (for example, landings and junctions) to strengthen loop closure.