GNSS RTX Positioning in SIRGAS Chile 2025.0

Trimble RTX is a high-precision GNSS positioning service based on PPP (Precise Point Positioning), available in both real-time and post-processing. This service allows for centimeter accuracy in real-time and millimeter accuracy in post-processing, in both horizontal and vertical components, without the need for a base station. RTX is available in both Trimble Access and Trimble Business Center, allowing for flexibility in various geospatial applications.

The diagram shows the RTX-RTK solution, using internet-based or satellite communication workflows


One of the most important aspects of RTX is its ability to determine GNSS positions in an instantaneous epoch, which allows working with the most up-to-date coordinate available. This advantage also presents the challenge of connecting these positions to the official geodetic framework in force in Chile, in this case SIRGAS Chile 2025.0, by employing a velocity model (VEMOS 2022, Figure 2). For this, Trimble has TGL (Trimble Geodetic Library), a tool that allows incorporating velocity or deformation models in an automated way.

Velocity model


In this experiment, we developed a comparison between the real-time RTX solution obtained through Trimble Access, reduced to the current reference frame, and a relative solution originating from an official SIRGAS Chile 2025.0 coordinate.

For the PP solution, 2 control stations with SIRGAS Chile 2025.0 coordinates were used. 3 test points were materialized with maximum vectors of 5 km between the control stations and the study area. The processing style considered transmitted ephemerides, a processing interval of 10 seconds, and the combined mode (1).

Adjusted solution


TBC configuration


For RTX-RTK positioning, observations were made using Trimble Access, configuring SIRGAS Chile 2025 as the reference frame, which includes the VEMOS2022 velocity model for epoch reduction. GNSS position logging was performed using the "topo point" option with 180 observations per point.

    Trimble Access Configuration

    GNSS RTX survey using Trimble Access

     

    GNSS RTX-RTK Survey - DA2


    To calculate the differences between the RTX-RTK solutions and the relative PP solution, a local geodetic system (SGL (2)) originating from the relative PP coordinate of each point was used. Table 1 presents the obtained results.

    POINT

    e (m)

    n  (m)

    u  (m)

    P4

    -0.013

    -0.001

    -0.050

    P5

    -0.006

    -0.001

    -0.021

    P6

    -0.010

    -0.003

    -0.037
    Comparison of relative positioning and RTX-RTK

     

    Conclusions

    The use of RTX-RTK positioning through Trimble Access allows for the automatic incorporation of a velocity model via TGL, ensuring the correct temporal updating of coordinates. This solution is suitable for applications requiring centimeter accuracy and consistency with the national geodetic framework, guaranteeing spatial coherence and reliability in the results.

     

    References:

    (1) Modernized Approaches for GNSS Baseline Processing in Trimble Business Center
    (2) Coordinate Systems in Geodesy. UNB