# RTX correction service

The Trimble Centerpoint RTX™ correction service is a high‑accuracy, precise point positioning (PPP) system that provides real‑time centimeter positioning without the need for an RTK base station or VRS network.

Survey using satellite‑delivered or internet‑delivered Trimble RTX corrections in open areas where terrestrial‑based corrections are not available. When surveying over a great distance in a remote area, such as a pipeline or utility right of way, Trimble RTX technology eliminates the need to continuously move the base station or, when using satellite‑delivered corrections, to maintain connection to cell coverage.

RTX subscriptions

If you have a Trimble receiver that supports Trimble RTX technology and has the appropriate subscription you can use the Trimble Centerpoint® RTX correction service.

The Trimble RTX subscription expiry date is displayed in the Instrument / Receiver settings screen.

Trimble RTX subscriptions which have been purchased as blocks of hours operate within a validity window, which is the start date and end date between which the number of hours/minutes purchased must be used.

For more information, go to positioningservices.trimble.com.

Configuring an RTX survey

To configure an RTX survey, create an RTK survey style with the broadcast format set to satellite RTX (SV) or an internet connection RTX (internet).

If you select RTX (internet) as the Survey type, in the Rover data link screen of the survey style you must create a GNSS correction source for the RTX internet service, with the appropriate Mountpoint name selected. See To configure a rover internet data link.

Convergence times

Typical convergence times depend on the region you are working in and the GNSS receiver you are using:

- If the GNSS receiver has Trimble ProPoint® technology, in most cases you should experience convergence in 1-3 minutes in RTX fast regions and 3-10 minutes globally.

- If the GNSS receiver does not have Trimble ProPoint technology, convergence will typically take 5-10 minutes in RTX fast regions and less than 15-30 minutes globally.

To learn more about the RTX service level in your area, visit https://positioningservices.trimble.com/en/rtx.

While the convergence times given are true in a majority of cases, the convergence time varies based on GNSS constellation health, level of multipath, and proximity to obstructions, such as large trees and buildings.

Reference frame

Coordinates measured in surveys using the Trimble CenterPoint RTX service are stored in the ITRF 2020 reference frame at the epoch of measurement. When you start an RTX survey, Trimble Access uses the local displacement model, or if no local model is available for your location, the software selects a tectonic plate in the global tectonic plate model, to propagate the ITRF 2020 coordinate from the epoch of measurement to the Global reference epoch for the job. Trimble Access then applies a datum transformation to transform the ITRF 2020 coordinate into the Global reference datum for the job.

RTX‑RTK offsets

As described above, Trimble Access transforms RTX coordinates into the Global reference datum for the job. However, there may be times that RTK data does not fit exactly with RTX data. For example:

- There are residual errors between RTX and RTK positions after the transformation.
- The RTK data is based on a Here key.
- The RTK data is based on a base station or VRS network that does not use the same Global reference datum as the job.
- You are working in an active deformation zone where the global tectonic plate model or the local displacement model does not give good results.

Trimble Access allows RTK data that is not in terms of the Global reference datum to be combined with RTX data in the same job by using an RTX‑RTK offset. These offsets are computed from a precise RTK point and a precise RTX point in the same physical location, and that difference is applied to all measured RTX points to bring them into terms with the RTK data in the job. The raw RTX measurements are stored, and the offset is applied when viewing coordinates or before performing any operations on those RTX measurements such as cogo calculations and stakeout.

When performing a site calibration using RTX measurements when there is an RTX‑RTK offset in the job, the offset is applied to bring the RTX measurements into terms with the RTK data before calculating the site calibration. Trimble recommends that you finalize a very precise RTX‑RTK offset for the job before performing a site calibration using RTX measurements.

When an RTX‑RTK offset is applied to a job, the precision estimates of the RTX measurements are inflated by the precision of the RTX‑RTK offset using the propagation of variances principle. The precision of the latest offset in the job is applied to all displayed and stored RTX measurements in the job. When the offset is updated, the precision of the new offset is reapplied to all RTX point measurements in the job.

Take great care to avoid changing the offset already in a job to a less precise offset, as this action may cause the precision of the points stored in the job to no longer meet the precision tolerances applied when the points were measured.

To compute an RTX‑RTK offset, see To compute an RTX‑RTK offset.