Constantly Innovating To Improve GNSS RTK Data Collection

2020-11-13

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Constantly innovating to improve GNSS RTK data collection

Niki Wong

Through the GNSS technology development, geographic data collection methods have also gradually improved. Real-time Kinematic (RTK) technology is frequently used in the topographic surveying, construction engineering and more. However, due to the hardware foundation of RTK data acquisition, the GNSS RTK receiver seems to have come to a halt in terms of development. The challenge of changing the homogenization and environment restriction is by breaking through traditions with technology innovation.

Technology, like art, is a soaring exercise of the human imagination. —— Daniel Bell

Technology is changing how we work and problems drives technology forward. While observing our users, we realized that the environmental limitations, and operating range plays an important role while they are on field work. With these findings, our objectives are to improve these features for our users.

Various Measurement Environments

Depending on the GNSS RTK data collection applications in the field, the measurement environments differ. There may be harsh situations such as poor network coverage, shaded areas or even unreachable points. How do we solve and improve our GNSS RTK receivers to work efficiently in these environments?

Traditionally, GNSS RTK receivers are often unreliable in remote areas where there is no correction data from the base or no network available. The global Precise Point Positioning (PPP) service solves this problem of poor network connection. For example, the released Hi-RTP technology adopts the global reference network data to generate and broadcast corrections from the L-Band signal that emits from the satellite. It provides global real-time CM-level positioning accuracy for rover users by GNSS real-time orbit and clock error estimating, high precision PPP post-processing, regional augmentation and other technologies.

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Hi-RTP Global Service System

Based on the Hi-RTP technology with the iRTK5 GNSS receiver, for example, measurements of offshore construction projects will be easier. The offshore working area is usually large, as there is no network signal with limited radio working distance. The traditional survey mode needs to set up the relay station to forward the different data in the middle, which is very troublesome. With just a single rover, the Hi-RTP service can help users to achieve CM-level accuracy.

Surveyors did a test at the Pearl River estuary in China and found that the initialization time is mostly within 3 minutes, the convergence time is within 10 minutes to reach a fixed solution, and the positioning accuracy is less than 3cm (horizontal) and 6cm (vertical). It meets CM-level positioning requirements for offshore constructions.

Actual results are as follows:

Test times	Collection points number	PPP service fixed rate	Vertical(m)	Horizontal(m)
Test times	Collection points number	PPP service fixed rate	-2σ~2σ(95.5%)	-2σ~2σ(95.5%)
1	23377	99.24%	0.056	0.023
2	23450	99.66%	0.058	0.024

Table 1 Hi-RTP Service Test Data

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Hi-RTP Service Test Site

Moreover, in the heavily sheltered environments, such as under tree canopy, signals of the GNSS RTK receivers are often unstable, thus the accuracy will be bad and may occur slip points. Therefore, the algorithm to improve the accuracy is particularly important. A new technique called quasi-dynamic measurement technology solves this problem. It is a self-developed technology of the iRTK5 GNSS RTK system, which greatly improves the surveying accuracy in the harsh environment through specific algorithms.

The most common situation that users will encounter is the need to measure corner points. As corner points are difficult to reach, the horizontal status of the GNSS RTK receiver is not guaranteed. With this in mind, the tilt survey method is needed more than ever. By optimizing the tilt survey correction algorithm, the procedure can boost efficient field work and minimize down time. This method is more practical and widely used in many engineering projects.

Limited Operating Range

When the measurement area is too large, people often worry that the operable range of the GNSS RTK receivers is unable to meet field working requirements. Thus, sustainable improving technologies of the radio, antenna, network and remote operation give ideas for solving this problem.

The multi-protocol built-in radio has become a universal compatibility requirement of the GNSS RTK receivers. With the omnidirectional antenna, the transmission distance can be greatly improved as seen in the iRTK5. The difference from traditional designs, it puts the omnidirectional antenna on top of the receiver, which increase the transmitting and receiving range more than 20% further.

iRTK5 Omnidirectional Antenna

Below is the comparison of test results in the built-in radio mode. It is clear that this newly designed device has a better performance in terms of distance from the base station. The overall performance improvement also makes it faster to reach a fixed solution during a slightly harsh environment.

Table 2 Built-in Radio Working Distance Test

Dist. to the base station	Traditional receiver	iRTK5
4 km	Continuously fixed	Continuously fixed
6 km	Occasionally fixed, unstable	Continuously fixed

Table 3 Field Fixed Time Test

Environment	Traditional receiver's fixed time	iRTK5's fixed time
At the foot of the mountain	65s	48s
In the forest	110s	60s

The popularity of the CORS (continuously operating reference stations) network technology has also made the network RTK technology more popular. With the local CORS network, it’s no longer limited to the traditional radio transmission mode. Most countries and regions have gradually entered the era of 4G networks. Full band support for the cellular mobile network (LTE, WCDMA, EDGE, GPRS, GSM) of GNSS RTK receivers can be helpful to the communication.

Furthermore, traditional GNSS RTK receivers barely support remote operations, but now, online firmware updates of receivers make people no longer dependent on the office and PC. And the built-in Web UI management system for real-time controlling and configuration makes the receiver operation more convenient.

Industrial-level Experience Needs

Does the industrial-level experience mean monotony? Absolutely wrong! Technology is used for innovation, it’s a means of improving the work efficiency and quality of life. Engineering projects applications are inseparable from the easy-to-use and reliable GNSS RTK receivers.

With touch screen smart phones being widely present in today’s everchanging landscape, Hi-Target integrating touch screens in the GNSS RTK receiver. iRTK5 is a case of this technology application. It contains one industrial OLED color touch screen for quick settings and status checking, making the field work more intuitive and convenient. In addition, the smart battery system supports quick charge and battery status indicating, users can estimate the working time and reduce work interruptions with greater battery capacity.

Intelligent Applications Bring the Better User Experience

Besides the good user experience of GNSS RTK receivers, reliable RTK engines and algorithms are also essential. Full constellations and multi-channels of the advanced GNSS motherboard has become the trend of GNSS RTK receiver engine development. More and more signals and data are applied to the GNSS algorithm, the processing speed and signal tracking capability will be stronger. Even in harsh environments, users can get a better experience than using traditional products.

Light weight, anti-drop, corrosion resistance and anti-interference have become the standard of industrial protection. Specific standardized designs and accessories are necessary to ensure the reliability of the field data collection. Details often determine the success or failure of one industrial-level GNSS RTK receiver.

GNSS RTK data collection modes won’t be invariable. With the innovation and development of technology, the receiver-based data acquisition will be on a new way. Technology will change our daily life continuously.

Every once in a while, a new technology, an old problem, and a big idea turn into an innovation. —— Dean Kamen

The Author

Niki Wong, the product manager of Hi-Target International Group Limited, specialized in RTK related solutions and marketing.

Anterior: A Glance of Hi-Target CORS

Posterior: Hi-Target CORS Applied in Zhuhai Beidou CORS Project

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