Trimble R12i as an internet base station

 R12i as an Internet Base Station

RTK is a real-time satellite positioning technique widely used in the world of geodesy and geomatics. RTK, which stands for Real Time Kinematics, has been successfully integrated into topographic workflows mainly due to its highly productive nature when carrying out topographic surveys. What characterizes RTK is its fast initialization, meaning that in a few seconds, an in-situ, precise coordinate linked to a reference framework is obtained, which makes a difference compared to PPK (Post Processed Kinematics).

Technically, RTK positioning requires a communication source that allows the transmission of differential corrections from the base to the rover. Traditionally, this has been addressed through the use of the UHF band, positioning itself as the most used solution for sending these corrections. However, the UHF band has some limitations related to the range and singularities of the work area which must be considered during the planning stage.

In relation to the limitations presented by UHF, the internet has been the answer to simplify RTK operation. The best example is the GEOCOM GNSS Network, an initiative that provides RTK differential corrections via the internet. The advantages offered by this methodology aim to optimize the logistics of a topographic survey: there is no need to install a GNSS base, achieving a gain in transport and mobility, and minimizing risks associated with prolonged installations. However, the GEOCOM GNSS Network is not present in all regions, and it is often necessary to look for itinerant installations, which are usually associated with GNSS base occupations with limited time intervals and corrections via UHF. However, why not consider an itinerant GNSS base that can transmit differential corrections via the internet? This is precisely what is achieved with Trimble R12i.

Figure 1. Trimble R12i GNSS Base / Thanks to MR Geomensura

Trimble R12i has the ability to transmit differential corrections over the internet; for this, the GNSS receiver has a SIM card slot which allows it to connect to the internet. Operationally, the UHF radio is replaced by a constant internet connection. An advantage of this technique is minimizing the power consumption of the receiver, which does not have to power the radio module. Another advantage is the reception of differential corrections since these only depend on the mobile device's internet connection; therefore, the baseline length can be extended as much as necessary (understanding the degradation of precision that occurs as the length increases).

Figure 2. R12i and its SIM card slot

By establishing independence from the range and taking into account relevant considerations regarding precision degradation as a function of distance, using this methodology allows the GNSS base to be installed in a protected location, avoiding equipment relocation with all the associated risks. In other words, if necessary geodetic precautions are taken, the base can be installed in any position, prioritizing security and internet connection over geodetic reference.

To illustrate the use of corrections via the internet, a case study is presented, illustrated in Figure 3. Here, 54 RTK baselines were determined through a control point observed in Trimble Access (180 seconds) from the EILA station of the GEOCOM GNSS Network, observing positions whose coordinates had been determined through a previous network adjustment. It is important to note that, although SIRGAS is the official reference frame for Chile, there are differences according to the epoch of realization; therefore, a specific geodetic network for a project does not necessarily have to coincide with the reference of the GEOCOM GNSS Network (which has currently been determined in the 2021.00 epoch). Finally, these 54 baselines allow the adjustment of EILA's coordinates so that its reference can be used in future topographic surveys under the RTK methodology. Table 1 presents results between the geodetic definition from the project and that referred to the GEOCOM GNSS network.

Figure 3. EILA adjustment using RTK baselines

Table 1. Differences for EILA coordinates

This same methodology can be employed under the concept of a roving base. Considering the connection via a SIM card, which allows the base receiver to operate in any position as long as there is mobile internet coverage, maintaining the nature of a roving base station, corrections can be sent to mobile GNSS receivers. In addition to this possibility, and for greater flexibility, it is also possible to use a connection via WiFi. Both options allow receivers to continuously transmit data within a local network or via the internet. Figure 4 shows a Trimble R12i base in roving operation.

Figure 4. Semi-permanent installation of Trimble R12i

Another important aspect is the autonomy of the roving base in its operation. In this sense, direct 220V power allows for continuous operation in places where an electrical grid is available. For this, the R12i power kit is designed for efficient and safe operation.

Figure 5. 220V power kit

For more details about the use of R12i, R12iLT, and R10, please contact soporte@geocom.cl

Frequently Asked Questions

➥ What is the accuracy of an RTK observation via the internet?

The same as one performed by RTK receiving differential corrections from a UHF radio. The technique does not change; the only thing that changes is the communication source.

➥ What is the maximum baseline length that can be observed?

In terms of communication, the maximum baseline length is undefined. As long as the mobile GNSS has a mobile internet connection, it will receive differential corrections from the base. However, it should not be forgotten that distance degrades the accuracy of an RTK observation. In these terms, the maximum distance to achieve survey-grade accuracy would be 30 to 40 km.

➥ What bandwidth is required?

Using CMRx and considering 12 satellites per constellation (GPS+GLO+GAL+BDS, 48 satellites in total) observing 3 frequencies per satellite, the differential correction, theoretically, does not exceed 600 bytes per second.

➥ Is this the same as NTRIP?

NTRIP is a protocol for transmitting GNSS data over the internet. Over time, it has become the industry standard for real-time GNSS. Although many GNSS receivers include NTRIP in their options, its use is not necessary in roving operations. All that is required is that the differential correction be sent through a communication medium to be received by a mobile receiver. In concrete terms, this is achieved through a fixed IP address and a port via a variety of communication protocols.

➥ I made a mistake entering the base coordinates, can an RTK survey be recalculated?

As long as you have the Trimble Access JOB, it can be recalculated in Trimble Business Center.

➥ I have a Trimble GNSS base that is not R12i / R12iLT / R10, can it transmit over the internet?

For compatibility details, please contact soporte@geocom.cl