4.3 PPK Positioning
PPK provides absolute coordinate alignment through post-processed GNSS, with no live NTRIP connection required in the field. Knowing when to choose it over RTK, and what the base station requires, determines whether it delivers usable results.
How PPK Works
PPK (Post-Processed Kinematic) is supported on the L3, the L2 Pro, and the K2. The base station logs raw GNSS data in RINEX format (the standard raw GNSS format) while you scan. Afterward, LixelStudio combines that file with the scanner's own raw log to compute a precise position for every point in the trajectory.
The L2 Pro captures its raw observations through the external RTK module. The K2 captures them through its built-in UM980 receiver. The procedures on this page apply to all three devices, and the minimums to the L2 Pro and K2.
RTK vs. PPK: When to Use Which
Both methods use GNSS for absolute coordinate alignment. The difference is when the corrections are applied. RTK applies them live during the scan, pulling corrections from a CORS network (a network of fixed GNSS reference stations) via NTRIP. PPK applies them afterward, processing the raw observations from the scanner and a base station together in software.
Choose RTK When
- Reliable mobile data covers the site throughout the scan
- A CORS network with NTRIP service covers the project area
- You need to confirm alignment before leaving the site
- The scan is primarily outdoor with good satellite visibility
Choose PPK When
- Mobile data is unavailable or unreliable (remote sites, basements with outdoor access, partial open sky)
- No CORS network covers the area, but you can set a base on a known point under 3 mi away
- Frequent NTRIP disconnections would interrupt an RTK fix
- A base station already logs RINEX for the project
PPK is not inherently more or less accurate than RTK. Both process the same observations; RTK does it live, PPK does it afterward with the full dataset. PPK can be more reliable where NTRIP is unstable, because the base data is complete regardless of what the mobile connection did during the scan.
Base Station Setup
PPK needs a GNSS base station running at a known position while you scan. The baseline is the distance between the base and the scanner.
- Set the base at a point with known survey coordinates, or one you will survey after the session
- Keep the baseline under 3.1 mi (5 km), and as short as you can make it; accuracy degrades as the baseline grows
- Give the base a clear, unobstructed view of the sky. Base multipath directly degrades PPK quality
- Keep the base antenna stationary the entire session. Any movement during logging invalidates that period
- Log RINEX 3.0 or later, and keep the base station's observation file and its navigation files. Confirm the files are complete before leaving; a truncated file cannot be used
- Start base logging at least 5 minutes before the scanner starts. At the end, stop the scanner first, then keep the base logging at least 5 minutes after the scanner stops. XGRIDS recommends more than 15 minutes of base deployment in total
- Record the start and end time of the scan. The RINEX file must cover that window with no gaps
Field Collection in PPK Mode
No NTRIP connection is needed, and the raw observations are stored on the scanner for processing later rather than corrected live.
- Set GNSS Mode to PPK before you record. Manual confirms (Lixel L2 Pro User Manual, FAQ 7; XGRIDS FAQ 217 for the K2): in LixelGO, open RTK settings, then Advanced Settings, and set GNSS Mode to PPK. The L2 Pro offers RTK, PPK and DJI; the K2 offers RTK and PPK
- Keep the antenna tilt within 20 degrees of vertical throughout the scan
- Include an open section where the sky is unobstructed, so the scanner observes enough satellites for a reliable trajectory
- Cover at least 33 ft (10 m) of open ground for minimum PPK viability
- Avoid scanning during high ionospheric activity. Solar events degrade GNSS and can make PPK unreliable even with good base data
- Do not power off the receiver during the scan. Raw logging is continuous; an interruption creates gaps that cannot be filled afterward
Minimum Requirements
Below these thresholds, PPK completes with compromised accuracy or fails to produce absolute coordinates.
- Baseline: under 3.1 mi (5 km). Shorter is better
- Open ground in scan: more than 33 ft (10 m) with clear sky
- Valid PPK data points after processing: more than 100, shown in LixelStudio after upload
- Base RINEX: RINEX 3.0 or later, with the base station's observation file and its navigation files, gap-free from at least 5 minutes before the scanner starts to at least 5 minutes after the scanner stops
- Antenna tilt: within 20 degrees of vertical throughout
Check valid points in LixelStudio before processing. The count appears after upload. Below 100 means insufficient GNSS quality, and processing will produce unpredictable accuracy. If it is low, review base placement, baseline distance, and whether the scan included enough open sky.
PPK Processing Workflow
PPK processing happens in LixelStudio.
- Transfer the Base RINEX FileCopy the complete RINEX file to the machine running LixelStudio. Confirm it covers the full scan window with no time gaps.
- Upload Scan DataTransfer the scan from the device and create a new project as normal.
- Load the Base Files and Confirm the Valid Point CountManual confirms (LixelStudio User Manual, Project Processing, PPK Module): click PPK Settings, load the base station's observation file and its navigation files, adjust the base station information, select the satellite systems, and click Calculate. LixelStudio then shows the valid point count. Confirm more than 100 valid points after PPK processing before proceeding.
- Set the Target Coordinate System and ProcessSet the source and target systems, ellipsoids, and projection for the deliverable, then process. The PPK trajectory is applied to produce the georeferenced point cloud.
Next: 4.4 Ground Control Points, the method for absolute accuracy indoors and anywhere satellite signals are unavailable.
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