XGRIDS Pro Guide™ / Module 4: Positioning

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, RTK from your own base, and PPK.

Section 1

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, your own base station set on a known point, or, for PPK, a base that logs raw data while you scan so the correction is computed afterward. In every case the result is the same: a georeferenced point cloud accurate to roughly 3 cm (1.2 in) RMSE.

Section 2

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.

GNSS Satellites raw signal 3 to 16 ft Scanner (rover) L2 Pro or K2 Logs raw GNSS observations CORS network Fixed reference stations at known positions Your base station At a known point within 3 mi of the scan Base station Logs RINEX during scan within 3 mi of the scan NTRIP corrections (real time) NTRIP from your base (real time) raw log RINEX (after the scan) Desktop software LixelStudio or LCC Studio LixelStudio applies the corrected positions Georeferenced point cloud ~3 cm (1.2 in) RMSE

Same destination, three routes. Whichever method you use, the output is a georeferenced point cloud at roughly 3 cm (1.2 in) RMSE. Confirm more than 100 valid points in the software before processing; a low count means the GNSS data was too poor to trust.

Section 3

Method Comparison

All three 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.

RTK via CORS / NTRIP

What it is
Live corrections streamed from a CORS network over a mobile data connection.
When to use
Outdoor sites with reliable mobile data and CORS coverage.
What you need
NTRIP credentials and a data connection that holds throughout the scan.
Confirmation
Alignment is verified on site, before you leave.
Critical risk
A dropped connection stops corrections, and that part of the trajectory cannot be recovered.

RTK via Your Own Base

What it is
Live corrections streamed from a base station you set on a known point.
When to use
Out of CORS range, but you can occupy a known point within 3 mi and stream corrections.
What you need
A base on a surveyed point, within 3 mi of the scan, broadcasting to the scanner.
Confirmation
Alignment is verified on site, before you leave.
Critical risk
A wrong base coordinate shifts the entire scan by that exact amount, with no warning.

PPK (Post-Processed)

What it is
The base logs RINEX while you scan; corrections are computed afterward in software.
When to use
No mobile data on site, or NTRIP too unstable to hold a fix.
What you need
A base logging gap-free RINEX within 3 mi, under 1 mi for best accuracy.
Confirmation
Alignment is confirmed in software after the scan, not in the field.
Critical risk
Any gap in the RINEX file invalidates that period. Confirm more than 100 valid points before processing.
Section 4

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 two RTK methods
  • 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 three 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
  • Base or CORS baseline: within 3 mi, under 1 mi for best accuracy
  • 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.

Previous 4.7 Hybrid Positioning Next Module 5: Project Scale

©2026 Alpine Reality Capture LLC  •  XGRIDS Pro Guide™  •  Site Disclaimer