3.4 Challenging Environments

Tunnels and Long Corridors

Tunnels combine repetitive geometry, low feature density, and length beyond what a single uncorrected trajectory tolerates. They need planned overlap, target-based alignment, and a processing mode that defaults off.

Overlap, Not a Length Limit

The governing rule on a long linear run is not how long the scan is. It is how often you cross ground you have already scanned.

• Plan a trajectory overlap at least every 500 m (1,600 ft). Come back across previously scanned ground at that interval rather than pushing straight ahead. Without it, the reconstruction layers: the same wall comes back as two offset surfaces.
• Where the site makes an overlap impossible, carry RTK or place relative control points beyond that distance instead. A single-bore tunnel with no cross-passage is exactly this case, and control points are the documented answer rather than a reason to give up on the run.
• Place segment boundaries at structural features (cross-passages, recesses, alcoves) that distinguish one segment's end from another's start.

Speed and Posture

• L2 Pro and K2: 1.6 ft/s or below throughout. Slower in low light.
• PortalCam: 1.0 ft/s. Its 1.6 ft/s figure is a ceiling for open conditions, not a tunnel speed.
• Side shuffle in tunnels under 2.5 m (8 ft) wide to keep both walls in view.
• Forward walk in wider tunnels at the same speed limit.
• Stay within the tilt limit for your device. The K2 and L2 Pro figures differ; see 3.1 Startup and Movement. Tunnels tempt operators to tilt down at the invert and up at the crown, which is the ceiling and ground supplement technique and is time-limited.

Multi-Segment Overlap

• Plan a shared overlap point at every segment boundary. The same physical location appears at the end of one segment and the start of the next.
• Mark the shared point within 10 cm (4 in) and 10 degrees of its position in the first scan. Tape the spot on the ground during the first segment so you can return precisely.
• Minimum spacing between shared points: 5 m (15 ft). Closer placements confuse alignment.

Control Point Placement Across Segments

• First segment: two control points at the end only.
• Last segment: two at the start only.
• Middle segments: two at the start and two at the end, four total.
• Same physical location, same point ID in every segment. This is how Map Fusion matches the point across sessions, and the names are case-sensitive.
• Minimum three control points per scan on every device, evenly distributed and not in a straight line. See Module 4: Positioning.

Target Placement

• Place high-contrast anchor targets in long featureless runs. 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. The K2 ships with 30 adhesive reflective stickers suited to this and they adhere to any flat surface.
• These are SLAM anchors, not survey points. They give the system reliable features to match between passes and need no surveyed coordinate to do that job. Attach surveyed coordinates in LixelStudio and the same target becomes a ground control point.

Record-Only Mode

Tunnels are the environment most likely to trigger it. The device keeps recording but stops generating a real-time point cloud, so the app shows only the camera feed.

• What causes it: degraded scenes (tunnels, utility corridors, mine passages, very narrow walkways, large flat areas with no elevation change) or extreme operation (rapid movement, shaking, sharp turns, prolonged tilt-limit violations, a blocked LiDAR, or a sudden change of space).
• What to do: stop and restart with corrected technique. Do not continue collecting for more than 20 minutes in this state; the data may not reconstruct.
• Watch the preview, not the recording indicator. The device looks like it is working normally.

Processing

Reflective Surfaces: Glass, Mirrors, Polished Metal

Reflective surfaces are the most common cause of indoor artifacts. LiDAR pulses pass through glass and bounce off mirrors, creating false geometry, and the cameras can track reflections as features.

Distance and Speed

• Stay at least 1 m (3.3 ft) from highly reflective objects where the route allows. Closer increases reflection exposure. The general minimum standoff from any scanned surface is 0.5 m (1.6 ft), and 0.5 to 1 m on the K2.
• Keep moving past any reflective surface. Never stop in front of glass or mirrors. A continuous walk produces fewer false observations and lets SLAM treat them as outliers. Use 1.6 ft/s on the L2 Pro and K2, 1.0 ft/s on the PortalCam.

Approach and Positioning

• Approach glass at an angle, 30 to 60 degrees, not head-on. Head-on maximizes reflection back into the sensor.
• Capture each reflective surface in a single sweep. Multiple passes add conflicting reflection data that degrades the surrounding cloud.
• Put your body between the scanner and the mirror where proximity is unavoidable. Useful in bathrooms with vanity mirrors and rooms with mirrored doors.
• Cross fully-glazed facades rather than walking parallel at close range. Parallel at 2 m (6 ft) for a long run is the worst case.

Materials That Will Not Capture Well

Fine wire mesh, carbon fibre, and other special reflective or transparent materials have limited capture quality on every device, and no technique fully recovers them. Where they are unavoidable and visible in the deliverable, set the client's expectation before the scan rather than explaining it after delivery.

PortalCam Sensitivity

The PortalCam is more affected by reflective surfaces than the L2 Pro and K2 because its 3DGS reconstruction leans on visual data. In heavily reflective spaces, use an L2 Pro or K2 for point cloud deliverables and add PortalCam coverage of less reflective areas only if 3DGS is required.

Dark Environments

Darkness degrades two of the three SLAM inputs at once: the cameras lose feature tracking and the LiDAR loses ambient reflectivity. The IMU continues, but with two inputs weak, drift accumulates faster.

Pace and Lighting

• 1.6 ft/s or below on the L2 Pro and K2, 1.0 ft/s on the PortalCam. Slower than that in genuinely dark spaces.
• Bring a portable light panel. Even 200 to 400 lumens of aimed fill light measurably improves tracking and color.
• Aim light forward into the area you are walking toward, not down at your feet. The upcoming area must be lit before you reach it.
• For static dark spaces, set up battery work lights before scanning. They give more even light than a handheld panel and free you to focus on posture.
• On the PortalCam, select the low-light scan mode for dark spaces and for any route that runs bright to dim and back.

Anchor Targets

• Place high-contrast anchor targets before scanning. Any flat, high-contrast marker works; the K2's adhesive reflective stickers are well suited.
• Even without surveyed coordinates, they give SLAM features to match when visual texture is minimal.
• Place them at intersections, doorways, and along long blank walls. Alpine practice is a reliable match every 10 to 15 m (30 to 50 ft) in dark areas.

3DGS in Dark Areas

• Color in dark spaces is poor regardless of technique. The cameras need light, and auto-exposure introduces noise and color shifts 3DGS cannot fully fix.
• Disable color for point-cloud-only deliverables, re-enabling for lit areas.
• For 3DGS in dark spaces, bring enough light for well-exposed images, or run the dark zones as separate no-color sessions. Joining a dark session to a lit one with Map Fusion gives clearly differentiated quality zones, which is often acceptable; mixing conditions in one session looks uniformly compromised.

Outdoor Scanning

Outdoor work adds variable weather, direct sun, large open areas with sparse vertical features, and wind.

Feature Density

• Keep fixed structures in the scan path. SLAM needs vertical geometry. An open plaza with no surrounding buildings is one of the hardest outdoor cases.
• Walk the edges of open areas where buildings, walls, or fences are visible, not diagonally across the middle with nothing in view.
• Use a loop-closure route, circular or serpentine, rather than a single-direction straight line.
• For very large sites, consider drone capture for the open areas and ground scanning for the perimeter. See Module 5: Aerial-Ground Fusion.

Sun and Direct Light

• Do not point cameras at the sun or scan into direct sunlight. Overexposure corrupts color for the entire scan, not just the bright frames.
• Keep the sun at your back where possible.
• Avoid scanning toward windows in bright sun from inside; the window overexposes against a darker interior.
• Prefer diffuse light: overcast, early morning, or late afternoon. Midday sun produces harsh shadows and overexposure.
• The PortalCam is rated for indirect sunlight only. Do not scan in direct sun for extended periods, and do not leave it in direct sun between segments. Heat soak exceeds the rated range well before ambient air temperature does.

Wind and Conditions

• Wind affects the PortalCam more than the heavier L2 Pro and K2. Walk with the wind where possible.
• Rain and snow degrade LiDAR. Airborne droplets return false pulses. Heavy precipitation makes outdoor scanning impractical, and the PortalCam carries no published ingress rating at all.
• Cold cuts battery life by roughly 20 percent below 41°F (5°C). Carry spares and keep them warm in an interior pocket until use.

Range Selection for Outdoor Work

The L2 Pro 32-300 reaches 300 m (985 ft) and is required for tall structures and large sites. The 16-120 and 32-120 reach 120 m (400 ft), enough for most indoor and small outdoor work but not tall facades. The K2 reaches 40 m (130 ft) at 10 percent reflectivity, 70 m (230 ft) at 80 percent, with a 100 m (328 ft) maximum, which suits indoor and close-quarters outdoor work but not tall facades or large open exteriors.

Featureless Corridors and Repetitive Geometry

Uniform walls, identical doorways at regular intervals, and no distinguishing features are SLAM's weakest case. Every position looks like every other from the LiDAR's view.

Movement

• Side shuffle in narrow uniform corridors to keep both walls in view, which matters most where SLAM has few anchors.
• Use diagonal paths in wider featureless spaces for perspective variation a straight centerline walk lacks.
• Branch into any available room or recess. Even a brief detour resets accumulated drift.

Targets

• Place targets at irregular intervals. Regular spacing matches the repetitive geometry; irregular spacing gives SLAM distinguishable anchors.
• Vary target placement between similar corridors. On identical corridors across floors, change target height or wall position per floor so SLAM can tell them apart.

When Multiple Challenges Combine

A dark featureless corridor with reflective windows combines three challenges; a glass walkway in sun combines two. Apply the most conservative technique from each category: the slowest applicable speed, anchor targets even if only one category normally requires them, and extra time. A compound zone that takes 10 minutes in normal conditions may take 25 with correct technique. Plan these zones explicitly, with their own segment boundaries, targets, and time. Field surprises at compound zones are how unrecoverable scans happen.