XGRIDS Pro Guide™ / Module 5: Project Scale & Map Fusion

5.6 Troubleshooting Fusion Problems

Diagnosing registration failures, misalignment, RTK conflicts, control point errors, and processing failures, and knowing which ones require returning to site.

Section 1

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 v4.0 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.

Section 2

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 segments. Review the RTK validity chart in LixelStudio for each segment that was planned as RTK-connected. Look for Fixed status, satellite count above 10, more than 33 ft (10 m) of movement while Fixed, and more than 100 valid RTK data points. Float status throughout the segment means RTK-based connection cannot succeed
Check control point names character by character. In 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 coverage. If 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 configurations. If a failing L2 Pro or K2 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. The L3 does not require control points for Map Fusion: its sessions are matched by region selection

Section 3

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 response is to reprocess the segment with the Mode set to Robust, or to Narrow Space 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, with position or orientation difference exceeding the recommended tolerance. 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 control point procedure.

A third cause is an overlap zone that was technically compliant at 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 80 ft (20 to 25 m) and ensure the area includes rich, stable geometry.

Section 4

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

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 more than 33 ft (10 m) 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 beyond 20 degrees can invalidate the RTK record, and the K2's device limit in RTK mode is 15 degrees. If the operator was carrying the scanner at an angle during fast movement, tilt violation may have invalidated the RTK record
Check that the segment logged more than 100 valid RTK data points. 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.

Section 5

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.

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, and it does not cost a return visit: control point names can be corrected after the scan by supplying a new spreadsheet of names.

Before treating the mismatch as a collection failure, 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. Where the names really do differ, supply the corrected names as a new spreadsheet rather than scheduling a rescan. XGRIDS publishes no click path for that step.

Insufficient Control 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

Control points marked more than 4 in (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.

Section 6

Processing Failures

Processing failures that are not related to data quality are almost always hardware resource issues.

Insufficient Memory Error

Close other memory-intensive applications and reprocess. If it still fails, reduce the number of segments in the fusion job. LixelStudio has no Low-Memory Mode; Low-Memory Reconstruction is an LCC Studio Single Model option and does not apply to fusion. If the project still exceeds RAM capacity, process it in two separate fusion jobs and merge the results in a subsequent step. Upgrading RAM is the permanent solution.

Timeout Error

Go 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 Crash

Verify LixelStudio is v4.0 or later. For L2 Pro panoramic video coloring, confirm the video is in time-lapse format and is at least 3 minutes in duration (verify in the panoramic camera processing utility associated with your L2 Pro panoramic camera workflow). Verify CUDA 11.6 or later is installed. GPU driver must be current. NVIDIA 20-series (RTX 2080 Ti) or newer is required for coloring; 10-series and older GPUs are not supported and will cause a crash. K2 panoramic coloring follows the same pipeline pending XGRIDS confirmation of K2-specific workflow differences.

Export Fails or Produces Corrupt File

For LAS to E57 or LAS to RCP conversion, shorten the LAS filename to 20 characters or fewer. Verify sufficient free disk space; LixelStudio v4.0 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).

Section 7

When to Return to Site

Some fusion problems cannot be resolved through any combination of settings changes, reprocessing, or post-processing workarounds.

Data that does not exist cannot be recovered. No processing setting creates overlap coverage that was not scanned. No software tool fixes a segment that failed SLAM optimization due to poor technique when reprocessing with Robust Mode also fails.

Conditions That Require Returning to Site

A segment fails SLAM optimization with the Mode set to Standard and again to Robust; the data is unprocessable and must be recollected. As a last resort before returning, try adjusting the mapping time range on the Project Settings panel to exclude the degraded portion of the trajectory. If the drift is concentrated at the end of the scan, trimming it may allow the remaining data to process
An adjacent L2 Pro or K2 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 control 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.

Next: 5.7 Connection Visual, a quick reference diagram for control point geometry and overlap requirements.

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