5.3 Field Collection for Fusion Projects

Segment Execution

Each segment in a fusion project is a fully independent scan session. All standard technique requirements (initialization, walking speed, device posture, loop route design) apply to every segment individually. A segment with drift problems cannot be saved by the fusion process. The algorithm aligns good segments to each other; it does not repair bad individual segments.

Starting Each Segment

Initialize each segment in a feature-rich, stable position with the scanner on its metal control point base on a hard, level surface. For the first segment, do not initialize in the overlap zone itself. Initialize in a well-structured area of the segment's unique coverage, then walk into the overlap zone as part of the scan route. This ensures the overlap zone is captured with a fully warmed-up SLAM track, not as the first few minutes of a session.

For subsequent segments, initialize within the overlap zone. With the back-to-back method below, Segment 2 starts exactly where Segment 1 ended: at the shared control point. The second segment captures the overlap zone from its own direction first, then proceeds into its unique coverage area. This is the opposite order from the first segment.

Within the Overlap Zone

Scan the overlap zone thoroughly. Move through it from multiple directions if the space allows. The algorithm needs strong feature data from both segments in the shared area to compute a reliable alignment. A single pass-through at normal walking speed is not as strong as a route that covers the overlap zone from two or three angles.

Ending Each Segment

End the segment after completing the overlap zone coverage, not before. The segment must include the overlap zone in its data, not just approach it and stop. With the back-to-back method, the segment ends with the device sitting at the shared control point. Wait for solid green before touching the device. Save confirmation is not optional on a multi-segment project where recollection of one segment may require recollecting all subsequent ones.

Marking Control Points

When consecutive segments are connected by control points rather than RTK, the shared points must be marked with exactly the same name in both segments. The strongest version of this connection is the official back-to-back method: the device never moves between the two takes, so the two marks are at the identical position and orientation by definition. Use it whenever segments are collected in sequence.

The Back-to-Back Connection Procedure

1. Scan Segment 1 Through the Overlap ZoneComplete coverage of the unique area. Enter the overlap zone and scan it thoroughly. When you reach the planned connection point, stop walking.
2. Lower the Device Onto Its Metal Control Point BaseSet the device down gently on a hard, level surface; avoid any ground-impact vibration. Not held in the air, not on a soft surface, not on a surface that vibrates from nearby equipment.
3. Mark the Control Point in LixelGOOpen Control Point Mode and enter the point name exactly as planned. Confirm the name before adding. A mistyped name here means a failed connection in post-processing.
4. Wait 15 Seconds, Then End Segment 1 Without Moving the DeviceLeave the device exactly where it sits. Stop the scan, wait for solid green, and confirm the save. The device has not moved since the mark.
5. Start Segment 2 From the Same SpotWith the device still in place, begin the new scan session and let initialization complete.
6. Mark the Same Point With the Identical NameThe device has not moved, so this take matches the Segment 1 take perfectly. The name must be character-for-character identical.
7. Rescan 50 ft (15 m) of Segment 1's AreaLift the device and cover at least 50 ft (15 m) of the overlap zone you scanned in Segment 1, from Segment 2's own track, before moving on.
8. Continue Into Segment 2's Unique CoverageProceed into new territory. The segment covers the overlap zone first, then the new area, not the new area alone.

Additional Shared Points at the Junction

Plan 2 shared points per junction, 3 for maximum reliability. The back-to-back method gives you one perfect point. Mark the additional points mid-scan in both segments: while covering the overlap zone, lower the device onto its base at the marked location, add the point, then circle it 1 to 2 times so the surrounding point cloud is complete before continuing. In Segment 2, mark the same locations with the same names while rescanning the overlap zone.

If Segments Are Collected Separately

When a junction cannot be collected back to back (different days, recurring rescans against a baseline), return to the same physical marker and replicate the prior take: device position within 4 in (10 cm) and orientation within 10 degrees. Note your exact position and body orientation when marking the first take, and photograph the scene. Mark physical locations with tape or chalk if you need to return to the exact position.

Tunnels and Narrow Space Mode

Long narrow environments (mine galleries, tunnels, corridors exceeding 1,600 ft / 500 m) require a specialized approach that combines Narrow Space mode with Map Fusion. Narrow Space boosts SLAM robustness in these environments, but it has limits. For runs exceeding 1,600 ft, long acquisition times, dynamic objects, and structural degradation in the environment all increase failure risk. The correct workflow is multiple shorter segments, each under 1,600 ft, merged via Map Fusion.

Control Point Requirements for Narrow Space Fusion

The control point placement rules for tunnel fusion differ from standard fusion. Because the environment provides limited surrounding geometry for feature matching, the algorithm relies more heavily on control point consistency.

Place 2 points at each connection, at least 16 ft (5 m) apart. The same physical location must receive the same point ID in every segment. Use the back-to-back method at the primary connection point whenever segments are sequential; it removes placement error entirely in the environment where placement error is most consequential.

No absolute coordinates are required for tunnel fusion. Relative control points are sufficient. The goal is structural consistency across the segments, not global position.

RTK Collection for Fusion Segments

For segments where RTK-based connection is planned, each segment must independently achieve valid RTK during collection. RTK validity is not shared across segments: if Segment 3 did not achieve Fixed status, it cannot borrow the RTK data from Segment 2 or 4.

RTK Validity Requirements Per Segment

• RTK status must reach Fixed, not Float or Single Point
• More than 10 valid satellites confirmed in LixelGO
• At least 33 ft (10 m) of movement while in Fixed status
• More than 100 valid RTK points logged during the segment
• RTK antenna tilt within 20 degrees during movement
• Any stretch without a Fixed solution must stay under 330 ft (100 m)

For multi-segment outdoor projects, confirm RTK status at the start of each segment before scanning significant coverage. An RTK signal that was Fixed during Segment 1 may be degraded during Segment 3 if cloud cover, multipath interference, or satellite geometry has changed. Check each time.

Quality Check Per Segment

The LixelGO preview after each segment serves a specific purpose on a fusion project: confirming that the overlap zone was captured adequately, not just that the unique coverage area looks complete.

After each segment, review the preview specifically for coverage in the planned overlap zone. The overlap zone should show dense, continuous point cloud data with no gaps. If the overlap zone has a gap, that segment cannot connect reliably to its neighbor. A rescan of the overlap zone is faster to execute now than to identify the problem after arriving back at the office.

Also confirm all control point names shown in the session log match your planned names exactly. If a name was entered incorrectly, that point must be remarked, which requires extending the current segment or planning a correction segment. Discovering a name mismatch during processing gives you no recovery option other than returning to site.

Before Leaving Site

End-of-Day Field Checklist

• All planned segments collected and saved (solid green confirmed for each)
• Segment count matches planned structure; no segments skipped or combined
• LixelGO preview reviewed for each segment; unique coverage and overlap zones confirmed
• All control point names confirmed against the planned name list, character-by-character verification
• RTK validity confirmed for all segments planned on RTK connection (Fixed status, satellite count, point count, no unfixed stretch over 330 ft / 100 m)
• No coverage gaps in any overlap zone
• All segment files saved to scanner storage and available for transfer
• Segment naming applied consistently; no files named scan1 or unnamed
• Any deviations from planned structure documented; note which segments deviated and how