XGRIDS Pro Guide™ / Module 4: Positioning

4.3 PPK Positioning

PPK is available exclusively on the L2 Pro. It provides absolute coordinate alignment through post-processed GNSS, no live NTRIP connection required in the field. Understanding when to choose it over RTK, and what the base station requirements are, determines whether it delivers usable results.

Section 1

RTK vs. PPK: When to Use Which

Both methods use GNSS to provide absolute coordinate alignment. The difference is when the corrections are applied. RTK applies corrections in real time during the scan by receiving correction data from a CORS network via NTRIP. PPK applies corrections after the scan by processing the raw GNSS observations from both the scanner and a base station together in software.

Choose RTK When

Reliable mobile data coverage is available at the site throughout the scan
A CORS network with accessible NTRIP service covers the project area
You need to confirm coordinate alignment before leaving the site
The scan area is primarily outdoor with good satellite visibility
Immediate feedback on RTK status in LixelGO is important for workflow confidence

Choose PPK When

Mobile data is unavailable or unreliable at the site (remote locations, basements with outdoor access, underground structures with partial open sky)
No CORS network covers the project area, but a base station can be set up at a known control point within 5 km
The project environment causes frequent NTRIP disconnections that would interrupt RTK fix
An existing base station with RINEX data logging is already established for the project

PPK is not inherently more or less accurate than RTK. Both methods process the same GNSS observations, RTK does it live, PPK does it afterward with the full dataset available. In practice, PPK can achieve higher reliability in field environments where NTRIP connectivity is unstable, because the base station data is always complete regardless of what happened to the mobile connection during the scan.

Section 2

Base Station Setup

PPK requires a GNSS base station operating at a known position while the L2 Pro scans. The base station records raw GNSS observations (RINEX format) that are later combined with the raw observations from the L2 Pro's RTK module to compute precise positions for every point in the scanner trajectory.

Position the base station at a point with known survey coordinates, or at a point you will independently survey after the session
The straight-line distance between the base station and the scanning area (rover) must be less than 5 km for reliable PPK processing. Minimize this distance wherever possible, accuracy degrades as baseline length increases
The base station must have a clear, unobstructed view of the sky. Avoid canopy, buildings, and any overhead obstruction, base station multipath directly degrades PPK quality
The base station antenna must remain stationary throughout the entire scan session. Any movement of the base station during logging invalidates the RINEX data for that period
Log RINEX data at 1-second intervals or finer. Confirm the RINEX file is complete before leaving the site, a truncated file cannot be used for PPK processing
Record the start and end time of your scan session. The base station RINEX file must cover this window with no gaps

Section 3

Field Collection with PPK Mode

From the L2 Pro's perspective, a PPK scan looks similar to an RTK scan. The RTK module must be attached and the scan must cover an area large enough to provide sufficient GNSS observation geometry for post-processing. The key differences are that no NTRIP connection is required, and the raw GNSS observations are stored on the scanner for later processing rather than being applied in real time.

Keep the RTK antenna tilt within 20 degrees of vertical throughout the scan, the same posture rule applies as for RTK
Ensure the scan area includes a sufficiently open section where the sky is unobstructed, the scanner needs to observe enough satellites in open sky to establish a reliable GNSS trajectory for post-processing
The required scan area must cover at least 10 meters of open ground for minimum PPK processing viability
Avoid scanning during periods of high ionospheric activity where possible, solar events and geomagnetic storms degrade GNSS accuracy and can make PPK processing unreliable even with good base station data
Do not power off the RTK module during the scan. PPK raw data logging is continuous, interrupting it creates gaps in the observation file that cannot be filled in post-processing

Section 4

Minimum Requirements for PPK Processing

These are the minimum thresholds for PPK to produce a coordinate-converted point cloud. Falling below them means the PPK processing will complete with compromised accuracy or may fail to produce absolute coordinate output at all.

Base station to rover distance: less than 5 km. Shorter is better, keep baselines under 2 km for optimal accuracy
Scan area coverage: must exceed 10 meters of open ground visible to the sky
Valid PPK data points after processing: more than 100, as displayed in LixelStudio after upload
Base station RINEX: continuous, gap-free logging throughout the entire scan window at 1-second intervals or finer
Antenna tilt: within 20 degrees of vertical throughout the scan

Check valid data points in LixelStudio before processing. The valid point count is displayed after upload and before processing begins. A count below 100 indicates insufficient GNSS observation quality, continuing to process with low valid point counts produces coordinate-converted output with unpredictable accuracy. If the count is low, review base station placement, baseline distance, and whether the scan area included sufficient open sky.

Section 5

PPK Processing Workflow

PPK processing is handled in LixelStudio. The raw GNSS observations from the scanner and the RINEX file from the base station are processed together to compute a precise trajectory, which is then applied to the point cloud to produce the final georeferenced output.

Transfer Base Station RINEX File to Processing Computer

Copy the complete RINEX file from the base station to the same machine where LixelStudio is installed. Confirm the file covers the full scan window with no time gaps.

Upload Scan Data to LixelStudio

Transfer the scan data from the L2 Pro to the processing computer and create a new project in LixelStudio as normal.

Import RINEX File and Confirm Valid Point Count

In the PPK configuration panel, import the base station RINEX file. LixelStudio will compute the PPK solution and display the valid data point count. Confirm this number exceeds 100 before proceeding.

Configure Target Coordinate System and Process

Set the source and target coordinate systems, ellipsoids, and projection parameters as required for the project deliverable. Proceed with SLAM processing as normal. The PPK trajectory is applied during processing to produce the georeferenced point cloud.

GNSS positioning covered. Next: ground control points, the method for achieving absolute accuracy indoors and in any environment where satellite signals are unavailable.

Ground Control Points →

Previous 4.2 RTK Next 4.4 Ground Control Points