4.8 Positioning Visual
One picture of how a GNSS correction travels from the satellites, through the scanner and a reference station, into a georeferenced point cloud. Switch the method to see what changes between RTK from a CORS network over NTRIP and PPK.
How Corrections Reach the Scanner
On its own, the GNSS receiver in the scanner knows roughly where it is, accurate to about 3 to 16 ft. That is far too coarse for survey work. A correction signal closes the gap by comparing the scanner's raw observations against a reference at a precisely known position.
The reference can be a CORS network you reach over the internet or, for PPK, a base that logs raw data while you scan so the correction is computed afterward. XGRIDS RTK does not support 1 plus 1 base-and-rover operation on the L2 Pro or K2, so live corrections arrive over NTRIP. In every case the result is the same: a georeferenced point cloud accurate to roughly 3 cm (1.2 in) RMSE.
GNSS Correction Signal Flow
The scanner always records its own raw GNSS log. What differs by method is where the correction comes from and when it is applied. Switch tabs to compare.
Same destination, two routes. Whichever method you use, the output is a georeferenced point cloud at roughly 3 cm (1.2 in) RMSE on the L2 Pro and K2. The L3's figure is under Key Specifications. Confirm more than 100 valid points in the software before processing; a low count means the GNSS data was too poor to trust.
Method Comparison
RTK over NTRIP and PPK deliver the same accuracy when their conditions are met. The choice is about site conditions: data coverage, CORS availability, and whether you need to confirm the fix before leaving. The third card records a route the scanners cannot use.
RTK via CORS / NTRIP
Your Own Base (1 plus 1): Not Supported
PPK (Post-Processed)
Reading the Diagram and Key Specifications
The line styles in the diagram map to the kind of data moving along each path.
- Faint dashed lines from the satellites are the raw signal every receiver sees, accurate on its own to only about 3 to 16 ft
- The solid colored link between the reference and the scanner is the real-time correction (RTK). It exists only on the RTK method
- The colored link from the base into the software is the RINEX file delivered after the scan (PPK). It exists only on the PPK method
- The green output node is the georeferenced result the two routes share
Key Specifications
- Raw GNSS, no corrections: roughly 3 to 16 ft
- Corrected output (RTK or PPK): roughly 3 cm (1.2 in) RMSE on the L2 Pro and K2
- L3 absolute accuracy: 2 cm (0.8 in) RMSE, horizontal and vertical, under open sky
- PPK base baseline: within 3.1 mi (5 km)
- Valid GNSS points required before processing: more than 100
Module 4 complete. Continue to Module 5 for project scale: Map Fusion, multi-session workflows, and connecting large sites into a single registered dataset.
©2026 Alpine Reality Capture LLC • XGRIDS Pro Guide™ • Site Disclaimer