Qinertia GNSS+INS Post-Processing Software (PPK)

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GNSS post-processing, or PPK, is an approach where the raw GNSS data measurements logged on a GNSS receiver are processed after the data acquisition activity. They can be combined with other sources of GNSS measurements to provide the most complete and accurate kinematic trajectory for that GNSS receiver, even in the most challenging environments.

These other sources can be local GNSS base station at or near the data acquisition project, or existing continuously operating reference stations (CORS) typically offered by governmental agencies and/or commercial CORS network providers.

A Post-Processing Kinematic (PPK) software can make use of freely available GNSS satellite orbit and clock information, to help further improve the accuracy. PPK allow for precise determination of a local GNSS base station’s location in an absolute global coordinate reference frame datum, which is used.

PPK software can also support complex transformations between different coordinate reference frames in support of engineering projects.

In other words, it gives access to corrections, enhances the project’s accuracy, and can even repair data losses or errors during the survey or installation after the mission.

Real-Time Kinematic (RTK) is a positioning technique where GNSS corrections are transmitted in near real time, typically using an RTCM format correction stream. However, there can be challenges in ensuring the GNSS corrections, specifically their completeness, availability, coverage, and compatibility.

The major advantage of PPK over RTK post processing is that the data processing activities can be optimized during post-processing, including forward and backward processing, whereas in real-time processing, any interruption or incompatibility in the corrections and their transmission will lead to lower accuracy positioning.

A first key advantage of GNSS post-processing (PPK) vs. real time (RTK) is that the system used on the field does not need to have a datalink/radio to feed the RTCM corrections coming from the CORS into the INS/GNSS system.

The main limitation to post processing adoption is the requirement of the final application to act on the environment. On the other hand, if your application can withstand the additional processing time needed to produce an optimized trajectory, it will greatly improve the data quality for all your deliverables.

Let’s imagine we have a 60-second GNSS outage in the middle of our survey. The position error in forward processing grows fast (rate depends on the IMU specifications and other parameters) and reaches its maximum at the end of the outage. It then quickly recovers. In post processing, we pretend that time flows backward and do the processing in anti-chronological order as the physical equations remains valid. In this backward processing, the error would be maximum at the actual beginning of the GNSS outage in a very symmetrical way to the natural forward processing.

Merging those two computation results in a maximum error around the middle of the outage, with a much lower magnitude than the forward only or backward only solutions.This will especially improve GNSS+INS solutions as allowed by SBG Systems products, but GNSS only processing will also benefit from this workflow.

As already stated, this improvement can only be done via post-processing, as you need all the data to be available from start to the end, hence delaying its use to the end of the survey.

Georeferencing is the process of aligning geographic data (such as maps, satellite images, or aerial photography) to a known coordinate system so that it can be accurately placed on the Earth’s surface.

This allows the data to be integrated with other spatial information, enabling precise location-based analysis and mapping.

In the context of surveying, georeferencing is essential for ensuring that the data collected by tools like LiDAR, cameras, or sensors on drones is accurately mapped to real-world coordinates.

By assigning latitude, longitude, and elevation to each data point, georeferencing ensures that the captured data reflects the exact location and orientation on the Earth, which is crucial for applications such as geospatial mapping, environmental monitoring, and construction planning.

Georeferencing typically involves using control points with known coordinates, often obtained through GNSS or ground surveying, to align the captured data with the coordinate system.

This process is vital for creating accurate, reliable, and usable spatial datasets.