About Amerisurv| Contact    
Magazine | Newsletter    
Flickr Photos | Advertise    
HomeNewsNewsletterAmerisurv DirectoryJobsStoreAuthorsHistoryArchivesBlogVideosEvents

Sponsored By

Software Reviews
Continuing Series
An RTN expert provides everything you need to know about network-corrected real-time GNSS observations.
Click Here to begin the series,
or view the Article PDF's Here
76-PageFlip Compilation
of the entire series
Test Yourself

Got Answers?
Test your knowledge with NCEES-level questions.
  Start HERE
Meet the Authors
Check out our fine lineup of writers. Each an expert in his or her field.
Wow Factor
Sponsored By

Product Reviews
Partner Sites







Spatial Media LLC properties




Home arrow Archives   The American Surveyor     

Remote Control Print E-mail
Written by Erik Dahlberg   
Friday, 22 September 2017

A 3.606Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

A new approach to precise GNSS positioning is cutting time and costs in remote locations.

In the remote northern portion of South Africa, projects are underway to tap the region's rich resources for wind and solar energy. The work is fueled by the country's drive to increase the use of renewable energy. In 2015, renewable sources in South Africa produced roughly 1,700 megawatts of electricity. South Africa's government wants to increase that number to 6,000 megawatts by 2020. The strategy is creating new opportunities and challenges for South Africa's surveying professionals.

Working with South Africa's national electric utility, independent power producers are building large wind and solar farms. By leveraging recent work to electrify South Africa's rail system (which effectively expanded and modernized parts of the national electric power grid), new farms can be built quickly and readily connect to the grid.

In the province of Northern Cape, planning for the Khobab Wind Farm included determining the location for 61 large wind turbines that will be capable of powering 120,000 homes. In addition to the turbine locations, planners defined the service roads, substations and power lines needed to build the wind farm and the 25-km (15 mi) connection to the national grid.

Khobab developers selected Cape Survey Ltd., a Cape Town-based surveying firm, to provide essential services for the project. Before construction could begin, Cape Survey needed to define the easements and rights-of-way for the land use agreements and servitudes associated with the project. They would also install control points for use by the construction crews by setting points at intervals of roughly 1 to 2 km (0.6 to 1.2 mi). South African regulations called for required accuracy of 10 cm (0.3 ft); the construction control points were provided with accuracy of roughly 2 cm (0.06 ft).

Working Without a Net
Cape Survey conducted initial surveys in 2014. While the Khobab site provided excellent conditions for GNSS, its remote location made it difficult to achieve the required accuracy and ties to South Africa's reference system. There was no connection to cellular service and the nearest survey reference station was more than 100km (62 mi) away.

Ian Thompson, a professional surveyor with Cape Survey, said his team used postprocessed static and real-time kinematic GNSS for the initial work. In order to create accurate control points, Thompson used Trimble R7 and R8 GNSS receivers for long-observation sessions. He processed the data using Trimble Business Center software to produce precise coordinates tied to the South African reference system. Cape Survey crews then used RTK to locate key points and to set out locations for planned roads, towers and other facilities.

Although the R8 and RTK was the best tool for the job, Thompson's team could not move as quickly as they wished. The gently rolling terrain often blocked RTK radio signals and regulations on radio output power further reduced performance. As a result, the team's RTK range was limited. They frequently needed to create new control points and move the RTK reference stations to cover the 25km x 30km (15 x 19 mi) site. Each move took at least an hour out of their already busy days.

While RTK provided the needed accuracy, it was a difficult process for this remote project. Knowing they would be working at Khobab again, Thompson needed a better solution.

As the Khobab Wind Farm neared completion in 2017, Cape Survey was called upon to verify the as-constructed locations of the farm's roads and power lines. The information would be used to finalize the servitude documentation. While Cape Survey would need to collect fewer than 50 points for the documentation, Thompson knew from the earlier experience that the work would be challenging. He budgeted three days for the job.

The Cape Survey crew arrived at Khobab equipped with a new Trimble R2 GNSS receiver and a subscription to Trimble CenterPoint® RTX correction service. The Trimble R2 and CenterPoint RTX provided precise real-time positioning without the need for RTK base stations or cellular connection to the Internet.

Using the Trimble R2 with a Trimble TSC3® controller running Trimble AccessTM software, the crew initialized their survey and began collecting points. They checked into the 2014 control points with good results and used the points to calibrate precisely to the project grid. Because they could work without ties to a RTK base, they could move freely--or as fast as the deep sand and rutted roads would allow.

Instead of the three days planned for the work, the Cape Survey collected all the needed points in just one day. The time savings made everyone happy--especially the surveyors. Instead of spending two nights in very uncomfortable accommodations--Thompson said they would have slept on-site in shipping containers--the crew returned to their homes.

Checking the Accuracy
In addition to the Trimble R2, the team also carried their Trimble R7 and R8 receivers, which would be used for RTK if needed. But that backup wasn't required, so the team set up the R7 and R8 to collect raw data on two project control points. Thompson later processed that data with data collected onboard the roving R2. He used postprocessed kinematic (PPK) techniques to double-check the RTX positions. "The RTX compared very well to the PPK results," Thompson said. "We were consistently around 20 mm accuracy." He added that the CenterPoint RTX solution initialized in 15 to 20 minutes and could be done while driving to the first points. Once converged, the satellite-delivered RTX solution could be held as the team moved around the site. "The main thing is time and cost savings and the consistent availability of the signals," Thompson said. "Field time is cut dramatically and we can use smaller crews."

The Cape Survey team and their clients were impressed with the performance of the R2 and RTX service. In addition to cutting the time on site by two-thirds, the system's accuracy consistently exceeded the project requirements. "The value of the system is clear," Thompson said. "On just this one job we've more than paid for the year's subscription to RTX."

Thompson said that CenterPoint RTX solution provides accuracy approaching RTK without the need for the additional equipment and processes. Cape Survey crews no longer need to carry RTK gear when working in remote areas. They are confident that the Trimble solution will provide the accuracy and reliability they need.

Erik Dahlberg is a writer specializing in the geomatics, civil engineering and construction industries. Drawing on extensive training and experience, Dahlberg focuses on applications and innovations in equipment, software and techniques.

A 3.606Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

< Prev   Next >

Marc Cheves, PS 
Editorial: A Great Year to be a Surveyor
Some magazines have what are called "theme" issues. That is, most of the content is focused on one particular subject. In my 22+ years of survey magazine publishing, my philosophy has always been to have a little bit of everything in each issue, thereby eliminating the possibility that ....
Read the Article
Jason E. Foose, PS 
Decided Guidance: Case Examinations: Halverson v. Deerwood Village
Whew! We really beat the snot out of Bryant v. Blevins and practical locations. Well this month we're back on new case that hit the Minnesota Supreme Court's docket in 1982. We've got the familiar gymnastics of jurisprudence featuring an extraordinary array of flying rope stretchers ...
Read the Article
Michel Philips 
Extreme Environment Surveying
A Franco-Chilean team of cave divers used the Nautiz X8 rugged handheld for marine cave surveying, gathering data to classify the inaccessible northern half of Madre de Dios for UNESCO World Heritage. The team of cave divers used the Nautiz X8 ....
Read the Article
Erik Dahlberg 
The Original Green Engineers
Sometimes, it's best just to leave things as you found them. That's the lesson shared by Dr. Richard Miksad and his students at the University of Virginia. As a result of studies covering nearly a decade, Miksad's teams have developed detailed ....
Read the Article
Dave Lindell, PS 
Test Yourself 49: No Dimensions
In square A-C-D-B with side S, C-E is tangent to the semicircle Q1 with diameter B-D. Q2 is the inscribed circle of A-C-E. The tangent to Q1 and Q2 meets the sides of the square at F and H and intersects C-E at t G. Q3 is the inscribed circle of C-G-H. What is the ratio of the radii of circles ....
Read the Article
Jerry Penry, PS 
Discovery on Grizzly Peak
When First Lieutenant Montgomery M. Macomb arrived in Carson City, Nevada, from Washington D.C., on July 28, 1878, his assigned survey crew from the 4th Artillery was waiting and ready for the new field season. At age 25, Macomb was the leader ....
Read the Article
Wendy Lathrop, PS, CFM 
Vantage Point: Fighting City Hall Over Land
Once upon a time (1989 to be exact) in a place not so far away from where I live, a man (Francis Galdo) bought a home across the street from a vacant parcel owned by the City of Philadelphia. That parcel, along with others, had been acquired by condemnation back in 1974 subsequent to a 1956 ....
Read the Article
Patrick C. Garner, PS 
Book Review: Boundary Retracement: Processes and Procedures
When I was in my mid-twenties and learning the honorable profession of land surveying, I was lucky to be guided by a mentor who would grab a book off his office shelf and say, "Every surveyor should have a copy of this!" The first example he waved at me was Davis, Foote and Kelly's Surveying ....
Read the Article


Amerisurv Exclusive Online-only Article ticker
Featured Amerisurv Events
List Your Event Here
contact Amerisurv


SXblue Announces
Premier Receiver

press [at] amerisurv.com
Online Internet Content


News Feeds

Subscribe to Amerisurv news & updates via RSS or get our Feedburn
xml feed

Need Help? See this RSS Tutorial

Historic Maps

post a job
Reach our audience of Professional land surveyors and Geo-Technology professionals with your GeoJobs career ad. Feel free to contact us if you need additional information.


Social Bookmarks

Amerisurv on Facebook 

Amerisurv LinkedIn Group 

Amerisurv Flickr Photos 

Amerisurv videos on YouTube 



The American Surveyor © All rights reserved / Privacy Statement
Spatial Media LLC
7820B Wormans Mill Road, #236
Frederick MD 21701
301-695-1538 - fax