PPK Georeferencing is a method of accurately positioning scan data using GNSS corrections applied after capture rather than in real time. It is supported on both Hovermap and GX1. Read this article before following the PPK workflow guides.
What is PPK?
PPK (Post-Processing Kinematic) is a GNSS correction method that georeferences scan data after capture rather than in real time. Instead of requiring a live correction link during the scan, both the rover and a base station record raw satellite observations throughout the mission. These recordings are processed together after the mission to produce a precise position trajectory, which Aura uses to georeference scan data.
This makes PPK well suited to remote or challenging environments where maintaining a live correction link is difficult or unreliable.
How PPK compares to RTK
RTK (Real-Time Kinematic) applies GNSS corrections live during the scan. This requires a continuous data link between the rover and a correction source throughout the mission. If that link drops, correction quality degrades.
PPK removes this dependency. The rover and base station record data independently during the scan, with no link required between them. Corrections are applied in the office after the mission is complete.
RTK | PPK | |
|---|---|---|
Corrections applied | During the scan | After the scan |
Requires live data link | Yes | No |
Affected by cell or radio dropouts | Yes | No |
Requires post-processing | No | Yes |
Additional software required | No | Yes (Emlid Studio) |
Key components
Rover
The rover is the GNSS receiver used to record satellite observations during the scan.
For Hovermap, the rover is an external GNSS receiver connected to the Backpack or Vehicle RTK kit. During a PPK mission, the rover records raw satellite observations continuously throughout the scan. These observations are saved as RINEX files and offloaded after the mission for processing.
For GX1, the rover is the integrated GNSS receiver. RINEX data is logged automatically when PPK is enabled in Commander and is included in the offloaded scan data.
Base station
The base station is a second GNSS receiver placed at a fixed point for the duration of the scan. It records the same satellite observations as the rover. After the mission, the rover and base RINEX files are processed together in Emlid Studio to calculate a corrected position trajectory.
Two options are available for base station data.
Local base station: Set up a supported GNSS receiver over a known point at or near the site before the scan begins. This gives full control over base data and works in locations with no network access. The known point coordinates are entered into Emlid Studio during processing.
GNSS correction network: A GNSS correction network is a permanent network of fixed GNSS receivers that log observation data continuously. If a network covers the area, base observation data can be downloaded after the mission instead of deploying a local base station. Check that the selected site provides high-rate data (1 Hz or greater) before relying on this option, as not all sites support it.
RINEX files
RINEX (Receiver Independent Exchange Format) is the standard file format used to store raw GNSS satellite observations. Both the rover and base station produce RINEX files during a PPK mission. These files are the input for Emlid Studio, which processes them together to produce a corrected .pos trajectory file.
The .pos file
The .pos file is the output of Emlid Studio processing. It contains a corrected position and timestamp for each point along the trajectory. This file is uploaded into Aura, where it is used to georeference scan data.
When to use PPK
PPK is suitable when RTK is unavailable or unreliable. Common scenarios include sites with no cell coverage, areas where GNSS correction network baselines are too long to maintain accuracy, terrain or structures that interrupt radio links between base and rover, and repeat monitoring jobs where setting up real-time comms on each visit is impractical.
Even when RTK is available and conditions appear reliable, Emesent recommends enabling RINEX logging on the rover as standard practice. If RTK quality is compromised during the mission, the recorded RINEX data can be used for PPK processing to recover accurate georeferencing in the office.
Next steps
To begin the PPK workflow, see Get started with PPK Georeferencing.