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 steel 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 (Segment 2 and later), initialize within or near the overlap zone. The second segment needs to capture the overlap zone from its own direction first, then proceed into its unique coverage area. This is the opposite order from the first segment. The overlap zone for Segment 2 is at the beginning of its route, not the end.

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.

If you are using control points for connection, mark them within the overlap zone. The procedure for this is covered in detail in the next section.

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. Double-tap the power button to stop recording. 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 procedure for marking control points is specific and must be followed precisely, the position consistency requirements are strict.

The Control Point Procedure

Tunnels and Narrow Mode

Long narrow environments, mine galleries, tunnels, corridors exceeding 1,600 ft (500 m), require a specialized approach that combines Narrow Mode with Map Fusion. Narrow Mode 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 Mode 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 the control point consistency.

Points within the same segment must be at least 16 ft (5 m) apart. The same physical location must receive the same point ID in every segment. Position and orientation consistency at shared tunnel control points follows the same best practice as standard fusion, within 4 in (10 cm) and 10 degrees, but is more consequential in this environment because surrounding geometry cannot compensate for a poor take.

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

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 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