In 2011, Trimble launched RTX (Real Time eXtended), an innovative solution that enables precise autonomous GNSS positioning, either in real-time or post-processing. RTX is defined as a GNSS correction service that allows users to obtain geodetic positions in real-time through corrections via satellite communication or the internet, worldwide, without the need for terrestrial infrastructure such as cellular networks, radios, or modems, and without using a base station. The same approach is used for post-processing, where the service performs advanced and intensive processing of observation files, providing precise coordinates. In this case, there is a direct relationship between long observation times and better precision.

 

 

Based on the SSR (State Space Representation) method, explained in depth in the article, Corrections Services Abound published by Gavin Schrock a few weeks ago in GPS World, RTX generates precise satellite orbit corrections, along with high-precision atmospheric models and clock corrections. The corrections are generated by using satellite measurements from a global network of GNSS ground tracking stations (Figure 1). In real-time, these corrections are transmitted to the receiver via regional geostationary satellites or the Internet, which the GNSS receiver uses to improve the precision of its positions by resolving biases in the observable carrier phase (Figure 2).

 

    Fig 1. RTX Infrastructure

     

    The RTX processing flow is presented in Figure 2. Initially, Trimble's GNSS network (1) performs continuous observations. This data is sent to Trimble's RTX processing center (2). Subsequently, a continuous stream of corrections is generated and made available to users, either via the internet or satellite communication (3). Finally, users access this service through GNSS receivers that feature RTX as a GNSS positioning method (4).

     

    Fig 2. RTX Workflow

     

    Experience in Chile, initial approaches, trust, and precision

    The emergence of RTX in the Chilean geospatial industry led to a significant increase in productivity across various sectors. Under the premise of precise, efficient, and reliable autonomous GNSS positioning, RTX spread exponentially throughout the national industry. This growth was accompanied by a strict validation process, which included a series of experiments to validate RTX.

    One of the first tests designed and carried out on RTX at GEOCOM aimed to evaluate the consistency and reproducibility of real-time solutions. For this, observations were recorded for 12 hours using an R12i receiver. In turn, these solutions were compared with differential RTK (NTRIP) positioning. Figure 3 presents the positions (coordinates) obtained for real-time RTX positioning projected (UTM 19s).

     

       Fig 3. Real-time RTX positioning

       

      Regarding the differential solution, Figure 4 presents the positions (coordinates obtained, baseline of ~12 km).

       

      Fig 4. RTK positioning (NTRIP). Baseline of ~12 km

       

      From the graph in Figure 3, the 12-hour variation in the North, East, and ellipsoidal height positions was approximately 6 cm, 5 cm, and 10 cm respectively. The same analysis was performed for 4 cm, 2.5 cm, and 4 cm. Based on these values, RTX can be considered an alternative for projects involving precise GNSS positioning.

      A second experiment considered RTX as a positioning source for generating geomatic products, in this particular case, a surface. As in the previous experiment, RTK was used as a comparison element. The created surface is presented in Figure 5.

       

      Fig 5. Comparison of surfaces obtained using RTX and RTK

       

      Based on the surface in Figure 5, a difference analysis was performed between both surfaces (RTX and RTK). The results obtained show an average difference of 2.7 cm between both surfaces.

       

      SIRGAS-Chile 2021, RTX within the national geodetic framework

      One of the characteristics of RTX is the epoch of the solution it provides. By performing an instantaneous calculation, its results are associated with the observation epoch, which may differ from a realization, for example, SIRGAS-Chile 2021. Considering this, during 2021, SIRGAS-Chile 2021 was implemented in RTX solutions, which allows, through a displacement model, to reduce the RTX position to the current national geodetic framework (SIRGAS 2010.0).

      Available in real-time and post-processing, sirgaschile.cl automatically links the RTX solution to the national geodetic framework. To validate this new feature, GEOCOM developed tests to evaluate the model's ability to perform the reduction. Figure 6 presents the displacement analysis with respect to the origin coordinate, defined under the national reference framework for the SANT (IGS) station.

       

      Fig 6. Comparison of positions for 24 months under an ENU system

       

      The results in Figure 6 indicate that the coordinate reduction to the official geodetic framework shows centimetric variations, allowing for diverse applications that require a precise and efficient methodology. More information about these analyses can be found in the following experiments:

       

       

      The integration of RTX in GNSS positioning has enabled the development of different projects under the premise of precision and efficiency. In parallel, the adoption of SIRGAS 2021.0 completes a robust solution that allows for the automated adoption of the current national geodetic framework. RTX is a reliable and precise alternative to address the main challenges posed by the geospatial industry.