5.6 Troubleshooting Fusion Problems

Reading the Error

Fusion problems fall into two fundamentally different categories: problems that can be resolved in post-processing with different settings or corrections, and problems that require returning to site because the underlying data is missing or wrong. Misidentifying which category a problem belongs to wastes time, either spending hours in LixelStudio on an unfixable problem, or returning to site for something that a configuration change would have resolved.

The first step in troubleshooting is identifying where the failure occurred. LixelStudio reports failures at the phase level. A failure during Individual SLAM Optimization is a per-segment quality problem. A failure during Alignment Computation is a connection data problem, RTK or control points. A failure during Global Optimization is typically a hardware resource problem. Each category has a different response.

Registration Failure

A registration failure means the algorithm could not compute a valid transformation between two segments. The segment pair has no established spatial relationship and cannot be included in the fused output. The rest of the project may process successfully; the failing pair's connection is the problem.

Diagnosis Sequence

• Verify RTK validity for the failing segmentsReview the RTK validity chart in LixelStudio for each segment that was planned as RTK-connected. Look for Fixed status, satellite count above 10, at least 10 meters of movement while Fixed, and more than 100 valid RTK points. Float status throughout the segment means RTK-based connection cannot succeed.
• Check control point names character by characterIn the project log, find the control point matching attempt for the failing segment pair. Compare the names used in each segment. A single character difference, a capital letter, a space, a number transposition, prevents the match. This is the most common cause of alignment failure on control-point-based fusion projects.
• Evaluate overlap coverageIf the overlap zone between the failing segments was in a stairwell, narrow corridor, or low-light area, the algorithm may have had insufficient feature geometry to compute alignment even if connection data was technically present. Overlap zone quality is a hard constraint, not a preference.
• Verify the connection pattern is one of the four valid configurationsIf the failing segment pair has no RTK and no shared control points, there is no valid connection regardless of how well either segment was individually scanned. The connection must be re-established in the field.

Visible Misalignment

Fusion completes without error but the result shows geometry that does not line up at segment boundaries: double walls, step offsets, or point cloud that diverges on either side of a transition zone. The fusion succeeded computationally but the alignment quality is insufficient for use.

Causes and Responses

The most common cause is drift within one of the segments that was not corrected during individual SLAM optimization. The fusion algorithm aligned the two trajectories as best it could given the available connection data, but one trajectory was already distorted before alignment began. The response is to reprocess the segment with Robust Mode enabled, or with Narrow Scene mode if it was a tunnel segment. If reprocessing does not resolve the internal drift, the segment data is not usable and must be recollected.

A second cause is a control point that was placed inconsistently between the two segments, position or orientation difference exceeding the 10 cm and 10 degree thresholds. The algorithm matched the names, but the inconsistent position introduced a spatial error that propagated into the alignment. This is visible as a consistent offset at the segment boundary rather than a smooth transition. The only resolution is recollecting the affected segments with corrected connection point procedure.

A third cause is an overlap zone that was technically compliant (50 ft / 15 m) but feature-poor. The alignment has low confidence and the resulting transformation is less precise. The response is to increase overlap in the affected zone during rescan, extend coverage to 65 to 82 ft (20 to 25 m) and ensure the area includes rich, stable geometry.

RTK Issues

RTK failures in fusion projects fall into two types: failure to achieve valid RTK during collection (a field problem) and LixelStudio reporting RTK as invalid during processing despite the field operator observing Fixed status (a processing problem).

Field Indicator Shows Fixed but Processing Reports RTK Invalid

This is a documented issue with a defined set of causes. Work through the following in order before concluding the RTK data is unrecoverable.

• Confirm the LixelGO app showed more than 10 satellites during the segment. The hardware indicator showing Fixed does not guarantee the satellite count met the processing threshold.
• Verify that at least 10 meters of movement occurred while Fixed status was confirmed in the app, not just while the hardware LED was green.
• Check RTK antenna tilt during movement. Tilt exceeding 20 degrees invalidates RTK data for those portions of the trajectory. If the operator was carrying the scanner at an angle during fast movement, tilt violation may have invalidated the RTK record.
• Check that 100 or more valid RTK points were logged for the segment. This count is visible in the LixelStudio RTK validity chart after import.

If none of the above applies and RTK data remains invalid in processing, process the affected segments without RTK using control point connections instead, or process without absolute coordinates and apply a coordinate system transformation in post-processing using surveyed control point coordinates.

Control Point Errors

Control point problems are the most frequent cause of fusion failure on indoor projects. Most of them were introduced in the field and cannot be corrected in post-processing.

Name Mismatch

If the control point name in Segment 1 is "CP01" and the same physical location was marked "cp01" in Segment 2, LixelStudio cannot match them. The algorithm is case-sensitive. The connection fails. There is no post-processing fix, the point must be remarked with matching names, which requires returning to site and rescanning the affected segments.

Before concluding a site return is required, verify the names in the LixelStudio project log. Sometimes a discrepancy is found that was introduced during manual entry in the app and the field notes confirm the correct name. LixelStudio allows manual control point selection in some configurations, check whether this option is available for the specific failure before scheduling a rescan.

Insufficient Connection Points

If an adjacent segment pair shares only one control point and that point has a quality issue, inconsistent position, poor surrounding geometry, or an environment with reflective surfaces, the connection will fail or produce poor alignment. One shared point per adjacent pair is the documented minimum; two is more reliable for all but the simplest projects.

Position and Orientation Inconsistency

Connection points marked more than 10 cm apart or with more than 10 degrees of orientation difference between the two takes produce spatial errors that the algorithm cannot fully correct. In feature-poor environments like tunnels, these errors are more consequential because there is less surrounding geometry to compensate. The only resolution is recollection with the correct procedure.

Processing Failures

Processing failures that are not related to data quality are almost always hardware resource issues. The resolution sequence is consistent regardless of which phase fails.

• Insufficient Memory errorEnable Low-Memory Mode in LixelStudio before reprocessing. If Low-Memory Mode is already enabled, reduce the number of segments in the fusion job. If the total project exceeds RAM capacity even in Low-Memory Mode, process the project in two separate fusion jobs and merge the results in a subsequent step. Upgrading RAM is the permanent solution.
• Timeout errorGo to Windows Settings, then System, then Power and Battery, then Screen and Sleep, and set both options to Never. This is documented as the primary cause of timeout errors during long processing runs. Open Task Manager and terminate any background processes consuming significant CPU or memory. Retry.
• Coloring failure or crashVerify LixelStudio is version 2.5.2.1 or later. For L2 Pro panoramic video coloring, confirm the video is in time-lapse format and is at least 3 minutes in duration (verifiable in Insta360 Studio). Verify CUDA 11.6 or later is installed. GPU driver must be current. 10-series NVIDIA GPUs are not supported for coloring.
• Export fails or produces corrupt fileFor E57 exports, shorten the filename to 20 characters or fewer. Verify sufficient free disk space, LixelStudio requires space equal to 2 to 3 times the raw data size during export. Verify the correct pose file selection (pose.csv vs. pose_no_offset.csv). For LAS-to-RCP conversion failures in ReCap, shorten the LAS filename to 20 characters or fewer.

When to Return to Site

Some fusion problems cannot be resolved through any combination of settings changes, reprocessing, or post-processing workarounds. Knowing when to stop troubleshooting and schedule a rescan prevents wasting days on a problem that will not yield to a software solution.

Conditions That Require Returning to Site

• A segment fails SLAM optimization in both Normal and Robust Mode, the data is unprocessable and must be recollected
• Control point names were entered with a mismatch and no manual correction option is available in LixelStudio
• An adjacent segment pair has no valid connection method, no RTK data and no shared control points, and the gap cannot be bridged from other segments
• An overlap zone has insufficient coverage (under 33 ft / 10 m) and alignment fails as a result
• Visible misalignment at a segment boundary persists after reprocessing with all available settings, the connection point procedure was inconsistent beyond what software optimization can compensate

When to Involve XGRIDS Support

For failures that do not match any of the patterns above, unusual error messages, crashes at unexpected stages, or results that are geometrically inconsistent in ways not explained by the known failure modes, contact XGRIDS technical support. Enable extended logging in LixelStudio's debugging options before the next processing attempt, and preserve the intermediate data files. Submit the poses.csv file along with a description of the failure. XGRIDS support can analyze the trajectory data to identify collection problems that are not visible from the point cloud alone.