Module 4 Quick Field Guide

Method Selection

Choose before scanning. It cannot be changed after. Full framework: 4.1.

• Relative only. No RTK, no GCPs. Local coordinates. As-builts, virtual tours, anything not tied to a real-world system
• RTK. Live GNSS corrections via NTRIP. L3 has survey-grade RTK built in; L2 Pro uses an attachable module; K2 has one built in. RTK cannot initiate a fix indoors
• Measure Point (L3 and L2 Pro). Carries absolute coordinates from an outdoor fix into an RTK-denied area. On the L2 Pro, 5 cm or better within 164 ft (50 m) of the point where RTK dropped, 10 cm or better within 328 ft (100 m). Requires a fixed solution before the loss and a qualifying route walked in advance, below
• Surveyed GCPs (GCP1). Markers with known coordinates, marked in the app during the scan. Correct method indoors and anywhere GNSS is unavailable
• Relative GCPs (GCP2). Targets marked without surveyed coordinates. Internal drift control only, no real-world frame
• Hybrid RTK + GCPs. Highest accuracy on the platform

RTK: Status and Thresholds

Status

Minimum Validity

• Status: Fixed before you start, and Fixed for most of the capture
• Satellites: more than 10
• Movement while Fixed: more than 33 ft (10 m)
• Valid RTK points logged: more than 100 for the published accuracy. K2 floor is more than 20 with a scan area over 33 ft (10 m), which converts but at reduced accuracy
• Unfixed-section max: L2 Pro 328 ft (100 m); K2 164 ft (50 m)
• Device tilt: L2 Pro within 20 degrees, RTK antenna within 20 degrees. K2 within 15 degrees in RTK mode
• Accuracy verification route: at least 328 ft (100 m) and not a straight line

RTK and NTRIP Faults

Read the two indicators together.

XGRIDS RTK does not support 1 plus 1 base-and-rover operation on the L2 Pro or K2. Corrections come from a CORS network over NTRIP, or you use PPK.

PPK: Thresholds

PPK is the alternative when NTRIP is unavailable or RTK will not hold Fixed.

• Base files: RINEX 3.0 or later. LixelStudio needs the base station's observation file and its navigation files; the observation file alone is not enough
• Base-to-rover: under 3.1 mi (5 km), and as short as you can make it
• Open ground in scan: more than 33 ft (10 m) with clear sky
• Valid PPK points: more than 100, checked in LixelStudio before processing
• Base logging window: start the base at least 5 minutes before the scanner starts, stop the scanner first at the end and stop the base at least 5 minutes after the scanner stops, gap-free throughout. XGRIDS recommends more than 15 minutes of base deployment in total
• GNSS Mode: set to PPK in LixelGO before you record. Manual confirms (Lixel L2 Pro User Manual, FAQ 7; XGRIDS FAQ 217 for the K2): open RTK settings, then Advanced Settings, and set GNSS Mode to PPK
• Antenna tilt: within 20 degrees of vertical

The L3 has survey-grade GNSS RTK built in, specified at 0.8 cm + 1 ppm horizontal, 1.5 cm + 1 ppm vertical, and XGRIDS lists PPK post-processing for it. The L2 Pro supports RTK, PPK and DJI GNSS modes, with DJI being aircraft-supplied corrections on the drone bracket. The K2 supports RTK and PPK.

Control Point Placement

• GCP1 (Absolute): surveyed coordinates attached in LixelStudio. Aligns the scan to a real-world system and corrects IMU leveling. Use when the deliverable needs absolute coordinates
• GCP2 (Relative): marked target, no surveyed coordinate. Constrains drift only. Use when georeferencing is not required
• The same physical target is either type. The difference is whether a surveyed coordinate is attached in LixelStudio

Count and Spacing

Minimum 3 control points per scan on the L2 Pro, K2, and PortalCam, regardless of how short the scan is. Use the tighter end of the spacing range in feature-poor spaces such as data center aisles.

Distribution

• Not collinear. Points on one straight line correct only one axis
• Even, not clustered. Spread points across the full scan extent
• At boundaries and transitions: floor changes, entries, where coverage paths cross
• Reachable: the scanner must be able to sit on each point during the scan

Marking

• Write point names on paper first. Type them into the CSV and the app from that list. Do not invent names in the field
• Use a floor-level target the scanner can sit on top of while staying vertical. Do not mark points on walls
• Set the scanner on the exact point, vertical, then add the control point with the exact name
• Hold stationary at least 5 seconds and wait for the confirmation that the point was added
• After the confirmation, lift slowly and circle the point once or twice before moving on. This gives the target enough coverage for automatic detection later
• Mark the same physical spot with the same name in every scan that shares it (Map Fusion). The L3 does not require control points for Map Fusion: its sessions are matched by region selection
• After the last point, keep scanning at least 15 seconds and walk a small loop before ending

Coordinate Setup Before the Scan

• Supported systems: WGS84, CGCS2000, and ITRF2008, with geodetic height
• L2 Pro direct absolute-coordinate output supports WGS84 UTM 3-degree zone and CGCS2000 Gauss-Kruger 3-degree zone only. Anything else is a post-processing transformation
• L3 real-time coordinate conversion supports WGS84 and CGCS2000 only. Anything else is a post-processing transformation
• Confirm the datum and ellipsoid your CORS network transmits (most networks outside Mainland China use WGS84)
• Have the target EPSG code for the deliverable ready before configuring RTK
• Match the RTK type to the module physically fitted. The L2 Pro offers Standard, Survey, and Aerial. Selecting the wrong one means processing applies the wrong parameters
• Wait about 5 minutes after changing the coordinate system. The device accepts the change immediately but takes time to apply it. Starting work inside that window is a silent error

Full configuration, datum transformations, and projection setup: 4.6.

Critical Warnings

• No recovery Georeferencing cannot be added after the scan. RTK must be active before recording. GCPs must be placed and marked during the scan. A scan delivered without it cannot be corrected without re-scanning
• No recovery Without more than 33 ft (10 m) of movement while Fixed, coordinate transformation is unavailable in processing. The scan still produces a point cloud, but it has no path to a real-world coordinate system
• Silent failure Mismatched GCP names are not matched automatically. The CSV name must match what you typed in the app, including case. No error appears, and the point is dropped. A name mismatch can be corrected after the scan by supplying a new spreadsheet of control point names, so it does not cost a return visit
• Silent failure Keep the RTK antenna within 20 degrees of vertical. Exceeding it can invalidate RTK data even when the indicator stays green, and the indicator is the only feedback you get in the field. On the K2 the antenna is built in, and the device stays within 15 degrees in RTK mode
• Warning Float is not a substitute for Fixed. Float embeds decimeter-level uncertainty that cannot be verified after the fact
• Warning Fewer than 3 control points is not a control network. Three is the minimum on the L2 Pro, K2, and PortalCam, and they must not fall on one straight line
• Warning RINEX gaps cannot be recovered. If the base station stopped logging during the scan, PPK for that period is degraded or absent. Monitor base status, and at the end stop the scanner first and the base at least 5 minutes after the scanner stops
• Warning Georeferencing does not fix poor technique. A scan with no loop closures and excessive speed still drifts, just with coordinates attached
• Warning A coordinate system change needs about 5 minutes to take effect. Do not start the scan inside that window