Movie! Network Corrections for 3D Machine Control

Coming soon to your job site

Randy Noland, Managing Editor, MCo

Movie Update!  - Amsterdam Network Excavator - 3D Machine Control - click here  

Network corrections for RTK positioning have been around for several years. I remember visiting Dr. Herbert Landau near Munich, Germany back in 1999 when I was working with Geotronics.  Dr. Landau was one of the first innovators of this technology. The purpose of my trip in 1999 was to explore the feasibility of creating a private, subscription based VRS network in North Carolina and Georgia. While that vision never materialized for me personally, both states are now blanketed with network coverage. Dr. Landau’s company, Terrasat was later acquired by Trimble and now their VRS network services are available across the globe. Along with Trimble, other companies including Leica, Topcon, Geo++ and others now offer some variation of network correction products. Locating these services for any particular area is much like locating your local GNSS equipment provider.

Initially, these networks were applicable to land surveying and GIS/utility applications; traditional GPS rover. But their use for 3D machine control was limited, at least in the early days, by latency and accuracy issues. As the technology continues to evolve, so has the adoption of machine control applications.  Now is the time to explore  reliable and cost effective network service providers for 3D machine control.

“Networks are a great way to manage that initial cost of outfitting your machine with a GPS system,” says Shawn “Shag” Greer of HemisphereGPS.  “A real-time network eliminates the need to purchase a costly base station.  Cutting the base station out of your initial purchase will save thousands of dollars and may make the difference in your decision to purchase.” (Greer, MachineControlOnline article Feb, 2010)

There are several types of network corrections and this article’s purpose is not to delve into those technical depths.  Rather the purpose of this article is to serve as a general overview. With that in mind, there are two types of Networks I will discuss:

  • Single-base Network correction
  • Multi-base Network correction

The single-base Network correction is just that, a single base station is used for the broadcast of correctional data. This is kindred to setting up a base station on your local site except the base station may be up to 20 miles away or more depending upon the level of precision being sought.

A multi-base Network correction uses data from more than one base station to compute an average or best fit solution to broadcast for your rover(s) by first computing a “virtual” base station on site. This is where the term VRS or “virtual reference station” is derived.  The advantage of multi-base is that the range between these base stations and the range from your rover(s) can be much longer.  Other approaches, such as Leica’s MAC (Master Auxiliary Concept) broadcasts information from multiple base stations and allow the rover to compute its own best position.

When a local base station is setup, typically a spread spectrum radio (900mhz) radio or UHF radio is used to broadcast the corrections. With Network corrections, the distance may be too great for these radios so two primary methods for delivering the corrections from either the single-base or multi-base Networks are typically used.

  • Internet
  • Cellular

Both have their advantages and challenges but their purpose is the same, deliver the base station(s) correction from point A to point B (and C, D, E....)

Rich Joslin, Support & Product Specialist at Sitech Norcal, says that the interest in internet base stations is increasing. “We have a base station set up at our office in Hayward, CA with a static IP. The corrections are broadcast via the internet to a job site.” Joslin adds, “We have a modem with a GSM cellular SIM card that communicates to the 900mhz Trimble radio and re-broadcasts the correction to multiple machines. By using the 900mhz radios, the correction broadcast is usually more reliable than using cellular to each machine.”

 

Lonnie Sears, PLS and president of eGPS, a network corrections provider in Georgia and Florida says, “The machines on eGPS service are being run through rebroadcasts. The contractors are using Intuicom RTK-Bridges with radios to rebroadcast out to their machines. This saves them the cost and hassle of setting up a base station at each site.”

As you can see, there are choices in how to best deliver network corrections for your particular application. At the left is my attempt to diagram some of these options. See Fig. 1

On Site Visit in Amsterdam
Ronald de Ronde of Bouw/Laser B.V. is a reader of our newsletter (thank you Ronald!) and invited me to a job site in Amsterdam near Schiphol airport a few months back.  Ronald is working with MNO Vervat B.V. on a highway project adjacent to Schiphol using 3D machine control that is using network services provided by Leica’s Spidernet network available across the Netherlands. In my next article, we will discuss with Ronald and representatives from MNO Vervat their project and how network corrections and 3D machine control are benefiting the project. I should also have some video footage shot during our day together so please stay tuned.

 

 

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