Q&A on the world’s Fastest GNSS RTK Rover: Leica GS18T

Dr. Xiaoguang Luo, Stefan SchauflerandBernhard Richterdiscuss the latest developments in the field of sensor fusion in GNSS and inertial measurement unit (IMU). The new Leica GS18 T GNSS RTK rover combines GNSS and IMU to automatically adjust pole tilt from plumb. Discover how this can increase productivity, extend RTK applicability and reduce human errors.

What are the current challenges of conventional RTK surveying?
这need of manually levelling the pole with a circular bubble and the phase centre position being reduced to the pole tip (by considering the antenna phase centre offset and the length of the pole), result in a number of disadvantages for the user:

• 在生产率方面，平整杆需要时间，尤其是在需要迭代重复的风险中。
• With respect to accuracy, holding the pole vertically is influenced by human errors and instrumental imperfections, such as a misadjusted bubble.
• Regarding applicability, it is not always possible to hold the pole vertically on a target point, for example, when measuring building corners.

In terms of solving the user’s problems: what are the major advantages of the Leica GS18 T?
这re are several benefits of the new rover:

• Free from on-site calibrations
• Immune to magnetic disturbances
• Applicable at large tilt angles
• Heading-aided 3D visualisation

这new Leica GS18 T GNSS RTK rover combines GNSS and IMU to automatically adjust pole tilt from plumb, which increases productivity, extends RTK applicability and reduces human errors. It improves the overall user experience beyond comparison.

Figure 1 - Leica GS18 T GNSS RTK rover with Leica CS20 field controller.

Leica GS18 T Rover如何回答对速度现场的不断增长的需求？
成为“世界上最快的GNSS RTK Rover”的定义是基于三个支柱的：IMU-basedtilt compensationtechniquein combination withinstantaneous RTK。这使生产率最高（准确性和可靠性 - 尤其是在地形调查中），并提供了与手动平衡杆进行测量相似的准确性。由于倾斜补偿，无需将POL升级，这使生产率平均比常规GNSS RTK测量实践提高了20％。此外，GS18 T还利用了MEMS IMU的高速加速度和角速度，以实时确定极点的态度。由于这些IMU测量不受磁场的影响，因此GS18 T不受磁干扰的影响，并且不需要任何耗时的现场校准。它可以从开箱即用，并且比基于磁力计的系统更快。

Figure 2 - Leica GS18 T as the fastest GNSS RTK rover with the IMU-based tilt compensation.

这re is always the question of accessing difficult targets – such as building corners and obstructed points?
With the GS18 T this is not considered a challenge anymore. Due to the IMU-based tilt compensation, the targets that were previously not accessible with GNSS, can now directly be measured with RTK, even at large tilt angles of more than 30 degrees. With the benefits ofadvanced signal tracking, the GS18 T is especially suitable for RTK applications where the sky is partially visible, for example, operating close to tree lines, under foliage or in urban canyons. By applying theIMU-based tilt compensationof the GS18 T, there is no limit to the maximum tilt angle as long as a sufficient number of GNSS satellites are tracked to be able to provide high-precision RTK solutions.大倾斜角are a problem of the past. The GS18 T is applicable to hidden point measurements (for instance hidden corners or points partly blocked by parked cars).

然后，这会直接影响在潜在危险的调查环境中测量的安全方面吗？
Exactly – without having to focus on levelling the pole, the user can pay more attention to his own safety. The risks of passing vehicles and operating machines are vastly reduced. In addition, attitude information is used to help users orientate themselves in the field by automatically updating the 3D visualisation of the surroundings (depending on the sensor orientation).

Figure 3 - Using the Leica GS18 T to measure building corners and obstructed points that were previously not measurable in conventional RTK surveying with a vertical pole.

It seems that you have successfully integrated two navigation sources, GNSS and INS?
Integrated GNSS/INS navigation systems which have long existed in the aerospace industry are now available in surveying applications. This sums up the successful integration:

Figure 4 - Schematic and simplified illustration of the GNSS/INS integration implemented in the Leica GS18 T.

一致性checks between GNSS and INS are carried out constantly to enable a robust system that can cope with extreme pole dynamics, such as hard shocks. Since no magnetometer measurements are involved in the computation of tilt-compensated positions, the GS18 T is immune to magnetic disturbances.

When directly comparing conventional RTK vs. tilt compensation RTK – have you performed tests to demonstrate the practical advantages?
为了证明使用倾斜补偿的好处，GS18 t针对露天A的露天天空和强大的多路径条件进行了基准测试。在开放式测试（图12）中，在瞬时模式下交替测量了两个已知的P1和P2，持续了10分钟。使用漫游者A，在进行瞬时测量之前，需要精确地平整杆，这对于由于倾斜补偿而导致的GS18 t并不是必需的。10分钟内测量点的数量代表了生产率的简单指标。

Figure 5 - RTK performance benchmarking under open sky by measuring two points alternately in the instantaneous mode for 10 minutes (Rover A vs. GS18 T, pole length: 1.800 m).

图6-在强多径环境（极长：1.800 m）中的RTK定位测试（a）带有金属外墙的建筑物附近的测量标记，（b）带有Leica GS18 T的倾斜补偿RTK测量。

Table 1 summarises the results from the open-sky test with respect to productivity and accuracy:

Table 1 - Comparison of the number of measured points within a 10-minute period and the resulting rms errors between GS18 T and Rover A (open sky, pole length: 1.800 m, instantaneous measurement).

而不需要水平杆、GS18 T团体nificantly reduces the time spent on a measurement, and thus increases the number of measured points by 33 per cent from 57 to 76 within a 10-minute period. In the tilt compensation case, despite the additional error from attitude determination, the 3D rms error is only 3 mm larger when compared to Rover A and amounts to 2.4 cm, which is acceptable for most topographic surveys.

表2总结了有关可用性，准确性和可靠性的结果：

Table 2 - Comparison of the availability, accuracy and reliability of RTK fixed positions between GS18 T and Rover A in a strong multipath environment (pole length: 1.800 m, instantaneous measurement).

Using the GS18 T with tilt compensation, the availability of RTK fixed solutions increases by 15 per cent when compared to conventional RTK using Rover A. The positioning accuracy is significantly improved, on average by 50 per cent. The reliability gives the percentage that the position error is less than three times the CQ, which is slightly enhanced by up to 6 per cent for the horizontal components. Please also keep in mind that such a strong multipath environment is considered as an extreme case and is far beyond the standard conditions relevant for accuracy and reliability specifications. In addition, points closer than 10 cm to a building cannot be measured with Rover A at all since in this case it is not possible to level the pole at the target point.

Cars, power lines and buildings with structural steel – every surveyor faces these and further local magnetic disturbances on a daily basis. Does the new Leica GS18 T offer a solution to this problem?
答案很简单：除了不需要现场校准外，基于IMU的倾斜补偿比基于磁力计的方法的主要优点是对磁场干扰的免疫力。我们比较了在磁干扰下的两个流浪者。查看表5中总结的RMS误差，GS18 T的2D精度比Rover B好约2 cm，而1D精度在相似的水平上：

Table 3 - Comparison of the rms errors between GS18 T and Rover B under magnetic disturbances (parking lot, pole length: 1.800 m, 1-s static measurement).

Looking at the rms errors summarised in Table 3, the 2D accuracy of GS18 T is approximately 2 cm better than that of Rover B, whereas the 1D accuracy is at a similar level.

经过comparing the 2D errors in Fig. 7a, the GS18 T provides higher accuracy and consistency than Rover B. Moreover, the 2D CQ estimates agree with the 2D errors, reflecting the positioning accuracy in a realistic manner. Regarding the results from Rover B in Fig. 7b, the 2D CQ values are significantly larger than the 2D errors if magnetic disturbances are detected, indicating unreliable tilt-compensated solutions. In this case, the user needs to repeat the measurement or to switch to the conventional RTK mode, which decreases productivity. Under certain circumstances, for example, when measuring points at larger tilt angles, the user would not be notified by a magnetometer-based system that the displayed accuracy cannot be achieved.

图7-在磁性干扰（停车场，极长：1.800 m，1 -S静态测量）下，GS18 T和Rover B之间的2D位置误差和CQ的比较。

How does including heading-aided 3D visualisation improve the overall user experience?
通过将传感器标准纳入3D可视化，用户可以轻松地将自己定向在调查环境中，并迅速朝目标点转向，从而提高用户体验和生产力。

图8-标题为3D可视化的示例，当左右GS18 T（开放天空，杆长：1.800 m）（a）导航视图，（b）朝西的视图，（c）朝南的视图，（d））朝东看。

Fig. 8 illustrates how the heading information helps when staking points with the GS18 T in the navigation view. If the stakeout point is more than 0.5 m away, the view shows the surroundings in the heading direction and follows the sensor from above and behind (Fig. 17a). The 3D view and stake instructions update automatically according to the current position and sensor heading, which changes from westward over southward to eastward in this example.

In your own words, how would you summarise the overall GS18 T advantages in comparison to other RTK rovers?
From a user perspective: usingtilt compensation, instantaneous measurement provides a similar accuracy level as static RTK measurement, along with a favourabletime-saving effect。

In comparison to conventional RTK with a vertical pole, tilt-compensating RTK significantly提高生产率by up to33 per cent相当大改善近建立的定位性能关于可用性和准确性。

在停车场与magnetic disturbances, the IMU-based tilt compensation produces更准确的位置和更现实的CQthan the magnetometer-based approach.

这IMU-based tilt-compensating RTK is applicable atlarge tilt anglesof more than30 degrees, where a3D positioning accuracy of 2 cmis still achievable.

经过incorporatingsensor heading into 3D visualisation在周围的环境中，用户可以轻松地将自己定向在测量环境中，从而提高生产率和用户体验。

这attitude informationof tilt-compensated RTK measurements isfully traceable, enabling quality assurance for users themselves and their clients.

To learn more about theLeica GS18 T, please visit:www.sendai-torema.com/gs18t

For in-depth information on high-performance GNSS signal tracking, the challenges in tilt compensation RTK and advanced signal tracking technologies, please download the white paper.