4.1 When Georeferencing Matters
Not every scan needs to be tied to a real-world coordinate system. When it does, the method must be chosen and set up before you scan. This decision cannot be corrected afterward. This page covers what each option means, when to use it, and what it requires.
Two Kinds of Accuracy
These terms are used interchangeably on job sites, but they mean different things and are solved by different tools.
Relative Accuracy
- How accurately the point cloud represents the internal geometry of the space
- The dimensional error between two points within the same scan
- Comes from good technique, consistent speed, and adequate loop closures (revisiting an already-scanned spot so the scanner can re-anchor)
- Does not require RTK or GCPs
- Fine for as-builts, renovation planning, virtual tours, and anything not tied to an external coordinate system
Absolute Accuracy
- How closely the point cloud registers to a real-world coordinate system
- The positional error at a point with a known survey coordinate
- Requires RTK, PPK, or surveyed ground control points
- Still requires good technique; georeferencing does not fix poor scan data
- Required for survey deliverables, site topo, and any model that must align with existing survey control
This decision cannot be made after the scan. RTK must be active before scanning begins. GCPs must be placed and marked during the scan. No processing step adds absolute accuracy that was not captured in the field.
Two Sources of Elevation Error
Georeferencing works the way it does because of how error arises. There are two distinct error sources in XGRIDS scans, and different methods address different ones.
IMU Leveling Error
The IMU (inertial measurement unit) cannot establish a perfectly level reference at startup, so a slight tilt is baked into the whole dataset. A floor that should be flat reads as pitched. RTK corrects this with an external coordinate anchor. Absolute GCPs (GCP1) with surveyed elevations also correct it, because LixelStudio uses their known heights to remove the tilt.
SLAM Drift Accumulation
SLAM (the scanner's simultaneous localization and mapping engine) builds the map as you walk by matching features frame to frame. Small matching errors compound over distance, so geometry far from the start point drifts from its true position. Ground control points correct this by anchoring the trajectory at known positions throughout the scan. Denser points mean smaller residual error between them.
RTK and absolute GCPs both remove IMU leveling error. Only GCPs constrain SLAM drift; RTK does not. Absolute GCPs (GCP1) are the single method that addresses both. The hybrid approach adds RTK's continuous alignment between the discrete GCP anchors.
The Five Positioning Options
A. Relative Coordinates Only
No RTK, no GCPs. A local coordinate system with the start point as origin and no relationship to real-world coordinates.
Use for as-built documentation, virtual tours, interior analysis, and any deliverable that does not register to an external system.
B. RTK Georeferencing
An RTK receiver applies live GNSS corrections via NTRIP, anchoring the trajectory to a real-world coordinate system as you scan.
The L2 Pro uses an external module on top of the scanner. The K2 has a built-in UM980 module with no attach step. Both correct over a mobile data connection.
Requires Fixed status throughout, more than 10 satellites, at least 10 m (33 ft) of movement while Fixed, and more than 100 valid points. RTK rarely reaches Fixed indoors; confirm in LixelGO before relying on it.
C. Ground Control Points with Surveyed Coordinates
Markers at known surveyed positions are marked in LixelGO during the scan and applied in LixelStudio, pulling the trajectory through each known position and constraining drift.
The correct method indoors, underground, in urban canyons, and anywhere GNSS is unreliable. Spacing at most 100 m (330 ft) for the L2 Pro and 50 m (165 ft) for the K2. Points cannot all be collinear.
D. XGRIDS Relative Control Points
Targets marked in LixelGO without surveyed coordinates. They constrain SLAM drift and improve internal accuracy but do not tie the scan to a real-world system.
Use when absolute georeferencing is not required but the scan covers a large area where unconstrained drift would be unacceptable: large interiors, multi-floor buildings, long trajectories.
E. Hybrid: RTK and Ground Control Points
RTK removes IMU leveling error and adds continuous alignment. Absolute GCPs remove leveling error and constrain drift at discrete anchors. Together they give the tightest constraint on both error sources and the highest accuracy on the platform.
Use for survey-grade deliverables, high-accuracy as-built comparisons, and any project whose accuracy spec requires addressing both error sources. Requires an active RTK connection and pre-placed surveyed GCPs marked during the scan.
When to Use Which
Use Relative Only (Option A or D)
- As-built documentation for renovation or fit-out
- Virtual tours and 3D visualization
- Interior space analysis and room measurements
- BIM models placed manually in project coordinates
- Any project where the client has not specified a coordinate system
- Indoor sites where RTK is unavailable and the budget does not allow GCPs
Use Absolute Georeferencing (Options B, C, or E)
- Survey deliverables tied to a national or local coordinate system
- Site topography that must align with existing survey control
- As-built vs. design comparisons on georeferenced BIM models
- Multi-site projects whose scans must register to each other
- Any project with a stated accuracy spec in absolute terms
- Construction progress monitoring requiring session-to-session consistency
Decision made. Next: 4.2 RTK Positioning covers hardware setup, NTRIP configuration, status indicators, and what valid RTK data looks like.
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