For what CORS – Efficiency or accuracy?

Grasping 21st Century CORS GNSS technology

For almost two decades, surveyors fought the communication battle. With the advent of RTK surveying, the necessity for communication between GNSS receivers was paramount to success. UHF radios were the best choice, powerful, light and efficient, however the logistical and environmental limitations of using UHF radio are enormous. Transmitting and receiving the correction data (RTCM 3.x) to complete the RTK positioning solution was a challenge; in fact, this alone became the biggest limiting factor in any survey.

Using Satel technology, Finland, Septentrio produced a receiver with much better range and robustness than competitors. This secured a position for Elliott Enterprises in the Philippine market…robust GNSS and robust UHF radio placed the Septentrio surveying products at the forefront.

Peer to Peer RTK Receiver System (Base and Rover) using UHF radios for communication

In the Philippines, the undulating, mountainous terrain with jungle type vegetation make surveying a challenge. In open, sparsely covered areas, distances between the Base receiver and the Rover can exceed 5 kilometres. This is the exception and far from the norm. Conditions for long distances for road design and construction are less than ideal. Limited to distances of 500 metres to 2 kilometres increase the time to complete a survey, in the 21st century time is money excessive time delays infrastructure projects. Accuracy also suffers each time a Base receiver is transferred to another site due to human error…but collection of surveying points was achieved!

All technology advances are a “leap frog” process; limitations of one era are overcome by another new technology, innovation drives progress. What better way to transfer data than the GSM (Mobile Phones). As Mobile Phones became a must-have, the installation of cell towers produced a more robust reliable communication system.

Septentrio AsteRx-SB CORS receiver and Septentrio VerraPhase 6000 antenna
Septentrio PolaRx5 and the Septentrio VerraChoke antenna (the ultimate in CORS technology)

Taking full advantage of the Internet and Smartphones, the GNSS manufactures were quick to take advantage of this. No longer is distance between the Base (Static) receiver and the Rover (Mobile) receiver limited. We now experience excellent quality positioning to over 50 kilometres from a Static Base (also known as a CORS [continuously operating reference station]). Of course, the correction data is available beyond 100 kilometres; though accuracy loss is cumulative over distance. Working in a 35-kilometre radius of the base provides near receiver accuracy (6-10 mm) (Septentrio NR3 rover) with little or no accuracy loss.

What are the Surveying Limitations?

The introduction and expansion of Internet and cellphone coverage; driving the expansion of Cell Tower Networks. The Base (static) receiver could now be installed permanently in the middle of a development zone ( LGU and Water District buildings). Installing the GNSS Antenna on stainless steel monuments permanently and securely on the building connected to a specially designed Static GNSS receiver connected to the Internet provides transmission of RTK correction data (NTRIP/RTCM 3.x) over a wide area.

Red Circle 35-Kilometre Radius – Yellow Circle 50-kilometre Radius

The CORS base station provides a robust, reliable solution. Rovers fitted with GSM (SIM) access the correction data. Completing this surveying concept now lie with the capabilities of the base receiver to provide high quality GNSS signal solutions. Choosing the Base receiver with the capacity to overcome the limitations is now the most important decision. Choosing the right Static base receiver (Septentrio PolaRx5 or AsteRx-SB receivers) and the matching Antenna technology (Septentrio Verraphase 6000 or VerraChoke) to satisfy local conditions is a job for the experts. This is where Elliott Enterprises is a specialist; using Septentrio GNSS receiver technology provides a robust, accurate, reliable solution.

Septentrio has been tried, tested and is recommended by International Scientific bodies (including UNAVCO) as the most robust, reliable, accurate receiver for a CORS installation. When comparing the available receivers, UNAVCO reported superior performance from the Septentrio PolaRx5 receiver in all aspects of the test. This Report was generated in 2016, 6 years later the Septentrio PolaRx5 is still number one.

What are the benefits for Surveying and Positioning?

A Static/CORS base receiver provides a number of benefits:

  1. The base or reference position is the same for every survey performed. The Elevation and Latitude and Longitude coordinates are computed to an accuracy of 5-15 mm on the earths surface. Height (Elevation) is computed relative to Sea Level. This means, in surveying terms, all positions and surveys conducted within 35 kilometres are relative and accurate to 10-15 mm (now and into the future).
  2. Up to 256 Rovers can be used simultaneously from one CORS receiver. Though rarely achieved, this freedom means government and private institutions can work without limitation together.
  3. Surveying and Position collection is a simple one-man process.
  4. Sharing data between agencies is an option, all surveys have a common reference point. Data collected for a Subdivision or road development can be shared with the LGU to develop a district wide data set or GIS model across the area. This has extensive benefits for development plans, budgeting and asset management. Water Districts can design water distribution systems with accurate height for more efficient supply to every household. This also reduces energy consumption and make leak and fault-finding easier.
  5. GIS (geographical Information System) is now part of every local and provincial meta-database. This is now a simple and data can be audited and trusted without expensive data auditing (comparing data sets with different accuracies.
  6. Surveys can be performed anywhere, a mobile phone signal is available. Surveying is as easy as taking the Rover receiver from the carry case, inserting the batteries, attaching the range pole and naming the project.
  7. Adding extra data or auditing a completed project is as easy as the original survey. Designs of roads, drainage and infrastructure can be accessed long after installation. Adding extensions and integrating new designs with old is now seamless.
  8. Locating a position or point at any time in the future is now possible; no searching for the original base point.

Where are they located?

Base stations are installed and operational across many regions across Mindanao and the dots are getting closer together. From Tacarong to General Santos City, Digos to Bislig and many more are programmed for 2022 and beyond

Case Study

Bislig LGU CORS installation

After consultation the Bislig LGU saw the benefits of installing a CORS receiver on the LGU building in Bislig, Surigao del Sur, Mindanao.

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Map displaying location of Bislig, North East Mindanao

Installing a CORS Base in your Area, not only benefits your surveyors. As the CORS receiver can simultaneously connect 256 Rovers, this equates to providing and extending the data to all contractors and utilities. As we embrace change and advances in the 21st century, the need for accurate positioning data is becoming an important part of life and all development.

Finding a suitable location for stable antenna monument is always challenge. With many years of experience in CORS Elliott Enterprises design the monument to suit the location, buildings and to provide the optimum antenna access to clean satellite signals.

To make sure the best and strongest signals are received by the CORS receiver the maximum antenna cable length is 15 meters. The CORS receiver is located according to cable length indoors where 240VAC power is available and within proximity to the Ethernet and the IT Room. The comuted position from the CORS receiver is out put to the ISP Router where the Receivers data port is Forwarded to the Internet.

Bislig LGU CORS Monument

DPWH CORS (Tier3) installed to International Standard

Selecting a cool, secure location for the CORS receiver is very important. Reliable power is also significant to provide an uninterrupted stream of correction data to the Rovers (surveyors) in the field.

CORS receiver installed at Bislig LGU.
DPWH Corsnet receiver and power management system

Correction data is captured via the GSM (SIM) in the Rover. Using the NTRIP (standard correction protocol) the Rover receives the correction data to use with the Rover position to secure and correct the position to the CORS coordinates (XY and Z (height). The correction data is a standard format, this allows all brands of Rover receivers to connect and utilize the correction in the RTK solution, however for the most accurate and robust surveying solution Elliott Enterprises recommend the Septentrio Altus NR3 Rover. This receiver provides the highest accuracy and precision available today. With our dynamic costing model, we tailor a solution price to meet your budget

Septentrio NR3 Rover providing the most ROBUST solution to all Surveying requirements

If you are interested in developing a CORS Base in your area, contact Elliott Enterprises for more information.

“We Support and We CARE”, and appreciate the opportunity to expand our technologies to advance all the people of the Philippines.