4.2 RTK Positioning

Hardware Setup

The XGRIDS RTK module attaches to the top of the L2 Pro scanner. 2 module types are available: Standard Type RTK and Survey Type RTK. Both use the same constellation channels (GPS L1/L2/L5, GLONASS L1/L2, BDS B1/B2/B3, Galileo E1/E5a/E5b/E6b) and publish the same accuracy specification: 0.8 cm + 1 ppm horizontal, 1.5 cm + 1 ppm vertical. The difference is antenna performance.

The Standard RTK module (2.8 dBi maximum gain) acquires and holds Fixed status reliably in open sky with minimal obstructions. The Survey-Grade RTK module (5.5 dBi maximum gain, ≤3 dB axis ratio) reaches Fixed faster and maintains it longer in degraded conditions: partial tree canopy, urban sites with adjacent structures, loading docks with overhead cover, and environments where reflected signals from nearby surfaces compete with direct satellite signals. The tighter axis ratio provides better rejection of multipath, the reflected signals that bounce off metal, glass, and concrete surfaces before reaching the antenna.

Select the correct RTK type on the LixelGO startup screen before scanning. The device applies different processing parameters for each module type. Selecting the wrong type can degrade position quality even if the module itself is functioning correctly. The K1 also supports RTK via a compatible module.

Before beginning any session with RTK:

• Confirm firmware version 2.3.0 or higher is installed on the L2 Pro, older firmware versions do not support RTK operation
• Attach the RTK module to the scanner and confirm the connection is secure
• Ensure the RTK antenna has a clear view of the sky, unobstructed by buildings, vehicles, overhangs, or any structure that would limit the visible satellite sky angle
• Keep the antenna tilt angle within 20 degrees of vertical during scanning, the same posture rule that applies to the scanner also protects antenna geometry
• Verify the module indicator light turns blue (connected, not yet fixed) before entering NTRIP credentials

NTRIP Configuration

RTK corrections are delivered to the module over the internet via an NTRIP (Networked Transport of RTCM via Internet Protocol) service. Your NTRIP provider will supply a host address, port number, mountpoint, username, and password. These are entered in the RTK settings screen in LixelGO before scanning.

Status Indicators

The RTK module has three hardware indicator states and a corresponding software status in LixelGO. Both must be understood before trusting the RTK data for any scan.

Minimum Validity Requirements

RTK data collected below these thresholds can be used to attempt coordinate conversion, but with compromised accuracy. Meeting all thresholds is required for reliable georeferencing.

Maintaining RTK Fix During Scanning

RTK fix is not guaranteed to persist throughout a scan. Buildings, trees, canyon walls, and overhead structures all attenuate satellite signals. When fix is lost, the scanner continues recording, but the trajectory during the unfixed period is not anchored to absolute coordinates.

After initialization and RTK fix confirmed, walk an L-shaped route of at least 10 meters on each leg before beginning the primary scan. This establishes a trajectory with confirmed geometry that the system can use to anchor the coordinate frame reliably.

• For the L2 Pro: any continuous unfixed section of the trajectory must be shorter than 100 m for RTK processing to remain valid across the full dataset
• For the K1: any continuous unfixed section must be shorter than 50 m
• Unfixed sections longer than these limits interrupt the continuity of the RTK trajectory and may cause processing failure or degraded georeferencing quality in affected portions of the scan
• Monitor RTK status in LixelGO throughout the scan, the satellite count and current status are displayed continuously
• When you anticipate entering an area that will block satellite signal (undercover parking entry, covered loading dock), note your position before signal loss and plan to exit through the same path if possible to restore fix continuity

RTK Indoors: What It Can and Cannot Do

RTK cannot initiate a Fixed solution indoors. The building structure blocks the satellite signals required to establish fix from scratch. However, a Fixed solution established outdoors before entering a building can persist as the scanner crosses the threshold, and the L2 Pro uses it to assign absolute coordinates to the indoor portion of the scan trajectory. This is a documented capability of the device, not an anomaly.

The practical limit is approximately 100 meters of scan path from the point where RTK was last active with Fixed status. Interior scan geometry within that 100-meter window receives absolute coordinate assignment from the carried-in fix. Beyond that distance, the RTK contribution diminishes and SLAM drift is no longer anchored to absolute coordinates by RTK alone.

Extending RTK Coverage Beyond 100 Meters with Map Fusion

For large indoor facilities where the scan area exceeds 100 meters from any single entry, RTK coverage can be extended by planning multiple RTK-initialized segments, each entering the building from a different access point with outdoor sky visibility. Each segment carries its own absolute coordinate frame from its respective entry. When those segments are registered together in LixelStudio using Map Fusion, the overlap zones between them allow the coordinate frames to connect across the full facility, even in areas where no single entry's RTK coverage reaches.

This approach requires deliberate overlap planning. Each segment must overlap an adjacent RTK-initialized segment by at least 15 meters of shared scanned area, and shared GCP sticker targets placed in the overlap zones give LixelStudio the anchors needed to register the segments at high confidence. The result is a facility-wide dataset with absolute coordinate coverage distributed from multiple entry points rather than a single threshold.

For areas that cannot be reached by any RTK-initialized path within 100 meters, ground control points with surveyed coordinates remain the correct solution. The 2 methods are complementary: RTK from entries covers accessible zones, GCPs cover the interior regions beyond reach.