5.3 Field Collection for Fusion Projects
Executing each segment correctly, marking connection points precisely, and confirming overlap quality before leaving site.
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. 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. Initializing in the overlap zone means your initialization point is in contested territory and the segment has no anchored start.
For each segment, begin in the planned unique coverage area of that segment. Work through the unique coverage completely, then enter the overlap zone. This ensures the overlap zone is captured with a fully warmed-up SLAM track, not as the first few minutes of a session.
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.
Review the LixelGO preview before starting the next segment. Check coverage in the unique area and in the overlap zone. A gap discovered now can be rescanned. A gap discovered during post-processing requires returning to site.
Marking Connection 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 connection points is specific and must be followed precisely, the position consistency requirements are strict.
The Connection Point Procedure
Scan Segment 1 Through the Overlap Zone
Complete coverage of the unique area. Enter the overlap zone. Scan it thoroughly. When you reach the planned connection point location, stop walking.
Place the Device on the Ground at the Connection Point
The device must be placed stably on the ground, not held in the air. Use a level, hard surface. This is the same requirement as initialization. Note the exact position. Note your body orientation relative to the device.
Mark the Control Point in the App
Open Control Point Mode in LixelGO. Enter the point name exactly as planned. The name must match what you will enter for this same physical location in Segment 2. Confirm the name before adding. A mistyped name here means a failed connection in post-processing.
Continue Scanning the Overlap Zone
After marking the point, continue scanning through the overlap zone for at least 50 ft (15 m) more before stopping the segment. The overlap zone coverage must extend beyond the connection point location, not end at it.
End Segment 1. Save Confirmed.
Stop the scan. Wait for solid green. Confirm save. Do not begin Segment 2 until Segment 1 is fully saved.
Begin Segment 2 in the Same Overlap Zone
Initialize Segment 2 at a feature-rich location within the overlap zone. Begin scanning. Cover the overlap zone thoroughly from Segment 2's direction, including the connection point location.
Mark the Same Connection Point Again
At the same physical location used in Segment 1, place the device on the ground again. Match your position and body orientation within 10 cm and 10 degrees of the Segment 1 take. Mark the point with the identical name. The name must be character-for-character identical to Segment 1.
Continue Into the Unique Coverage Area of Segment 2
After completing the overlap zone, proceed into the unique territory of Segment 2. The segment should cover the overlap zone and then the new area, not just the new area alone.
Position and orientation consistency at connection points is critical. The device position must be within 10 cm and the orientation within 10 degrees of the previous take at the same location. This is not an approximation, it is the stated requirement. On reflective or feature-poor surfaces, where the algorithm has less surrounding geometry to work with, consistency at the connection point becomes the primary alignment anchor. Mark physical locations with tape or chalk if you need to return to the exact position.
Tunnels and Narrow Mode
Long narrow environments, mine galleries, tunnels, corridors exceeding 500 meters, 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 500 meters, long acquisition times, dynamic objects, and structural degradation in the environment all increase failure risk. The correct workflow is multiple shorter segments, each under 500 meters, 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 connection point consistency.
Points within the same segment must be at least 5 meters apart. The same physical location must receive the same point ID in every segment. Position and orientation consistency requirements at shared tunnel control points are 10 cm and 10 degrees, the same as standard fusion, but 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 10 meters 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.
Plan a fallback for RTK segments. Even on projects planned as RTK-based fusion, identify possible control point locations at each segment break. If RTK fails to achieve Fixed status for a segment, having physical control points marked gives you a recovery path without returning to site.
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
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