After the mission, a Post-Processed Kinematic (PPK) software gives access to corrections and brings your project to the centimeter accuracy, enhances the overall project, and repairs some data loss during the survey or installation error. In other words, it can save the day!

Mainly used with high-end IMU/GNSS systems, post-processing is now accessible to all surveying applications, even with the powerful Virtual Base Station (VBS) mode.

How does Post-Processing Work?


Photo: Composition of SBG Systems INS GNSS

An Inertial Navigation System, also called INS, embeds an IMU (Inertial Measurement Unit) that contains gyroscopes, accelerometers, and sometimes magnetometers on the one hand, and the GNSS (Global Navigation Satellite System) receiver on the other hand. In real time, navigation systems use “causal” filters such as Extended Kalman filter. This means that they can estimate navigation parameters based on past and present data only. This will never be as good as what can be done in post-processing once we have collected the whole survey data set from beginning to end.

An INS with datalogger allows post-processing, which gives access to new possibilities such as processing the data backward, starting at the end of the file and going back in time to the beginning of the file. This combination or merge of forward and backward processing with some smoothing provides a better accuracy that would never be possible in real-time acquisitions.

Post-Processing – Forward/Backward/Merge Algorithm

iMU GNSS Post-Processing with Forward and Backward Merge

Photo: SBG Systems

The example shows how this forward, backward, and merge processing improves the data accuracy. We can see that the position error in forward processing grows exponentially until the GNSS is back after 60 seconds. The same can be seen in the backward data where we lose the GNSS at 60 seconds, and the error grows exponentially until the GNSS is back at the 0-second mark. When we merge and smooth this data, the error is decreased significantly, with the highest error value being in the middle of the GNSS outage.

INS/GNSS Post-Processing Advantages:


Automotive Post-processing test in an urban canyon. The yellow dots picture the GNSS positions while the others represent inertial trajectory.

The Virtual Base Station to Maximize Corridor Survey Accuracy

The Virtual Base Station (VBS) consists in computing a virtual network around your project in which position accuracy is maximized, homogeneous, and robust. Surveyors can collect data far from base stations or over large areas, making it ideal for corridor mapping.

How does a Virtual Base Station Work?

Virtual Base Station


Photo: SBG Systems

Traditional RTK algorithm performance is degraded as baseline increases because of atmospheric disturbances. The VBS is a sophisticated algorithm developed to extend the coverage area of RTK by using a network of base stations available around the trajectory.

The VBS first creates a map of atmospheric errors along the whole vehicle trajectory. These errors are then compensated in Qinertia PPK solution to maintain a higly accurate navigation solution, even in challenging conditions, or in long distance corridor surveys.

Photo:Qinertia VBS implementation is particularly efficient in processing VBS networks, with a distance from the rover to the bases easily reaching up to 100km or more. This feature greatly extends the availability of PPK.

Watch the demonstration of a VBS generated by Qinertia, SBG’s in-house post-processing software.


Post-processing Accessible to All Surveying Applications

Conway quay wall, Conway bridge and Cob surveyed using the Accesion 350 USV, SONIC 2024, Apogee Navsight and Merlin Laser

LiDAR Mapping with Navsight INS and Qinertia SBG Systems INS for LiDAR and Sonar on board an USV

The UK-based company Unmanned Survey Solution (USS) has created this unique Unmanned Surface Vessel called the “Accession Class USV” equipped as standard a multibeam echo-sounder coupled with a mobile LiDAR for mapping terrestrial structures to create a full 3D point cloud above and below water. “In such situations, the centimetric level RTK position accuracy is greatly improved using SBG’s post-processing software called Qinertia. This PPP and PPK capable software offers single or virtual base station modes and can even incorporate users’ own base station RINEX data”, explains James Williams, CEO of USS.

Post-Processing Accessible to All Surveying Applications

Photos: SHOM, Courtesy Photo 512th Engineer Detachment, Viametris, ASTRALiTE

Shom hydrography vessel with Navsight INS GNSS Backpack Mapping of American Military Cemeteries with SBG Systems’ INS Mobile Mapping system with SLAM, GNSS, and INS Topographic and bathymetric LiDAR for UAV with INS GNSS

Post processing is now affordable and accessible to all surveying applications such as UAV-based surveying, Backpack or car-based mobile mapping, or hydrography.


Qinertia: One PPK Software for All your Projects

IMU GNSS Post-Processing and VBS on Qinertia PPK Software

Qinertia is SBG Systems’ in-house GNSS (Global Navigation Satellite System) and INS post-processing software. It gives access to offline RTK corrections from more than 7,000 base stations located in 164 countries

SBG Systems INS and GNSS Post-Processing Software Qinertia

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This page was produced by North Coast Media’s content marketing staff in collaboration with SBG Systems. NCM Content Marketing connects marketers to audiences and delivers industry trends, business tips and product information. The GPS World editorial staff did not create this content.