GNSS Interoperability - Mixing Receiver Brands on the Same Job Site

Randy NolandI have received several emails over the past few months asking about using different brands of RTK GPS receivers together on the same job site. Questions such as “Is it possible to use a..."

  • Trimble base station with a Topcon rover?
  • a Leica or Septentrio rover with a Javad GNSS base station?

  • what about a legacy Topcon receiver with Ashtech or Navcom rovers?

The short answer is yes. However, a basic understanding of how real time kinematic (RTK) GPS positioning, communication protocol and GNSS constellations is important.

The Basics
In its simplest form, Global Positioning System (GPS) is a space-based global navigation satellite system (GNSS) that provides location and time information in all weather, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. The GPS constellation is maintained by the United States government and is freely accessible by anyone with a GPS receiver with some technical limitations that are only removed for military users. The required minimum number of satellites to provide visibility (thus a positional solution) for 95% of the earth is 24. This defines a functional, constellation.

There are other satellite systems or constellations provided by other government agencies around the globe. Here is a current list but know these change over time as additional constellations are planned and new technology emerges.

GPS - United States
GLONASS - Russian Federation
GALILEO - European Union

It is worth mentioning that while GPS, GLONASS, GALILEO and COMPASS are the generally recognized GNSSs, a discussion of further navigation satellite systems would not be complete without mentioning Space based Augmentation Systems (SBAS) and Regional Navigation Satellite System (RNSS). I will only mention these for now as other possible sources for positional data.

Multi-GNSS receiver
As noted above, there are multiple sources for GNSS data. In order to utilize all the additional signals, the receiver must be designed to receive and process more than one satellite system. Multi-GNSS offers significant opportunities and challenges to GNSS technology, system and application developers. As navigation and positioning applications become more widespread, end user demands are increasing. Multi-GNSS offers opportunities to improve performance to meet increasing user demands. Benefits can also include improved integrity, continuity and accuracy, depending on the situation and priorities of the application. 3D machine control is considered a demanding application due to the speed of the machines and the impact on the increased productivity. If a machine is positioned incorrectly, the consequences can be very expensive so any technology or procedures that improve performance are of course welcome.

Delivering Corrections - Real Time Kinematic (RTK)

Above we talk about using one receiver, whether single or multi-GNSS compatible. This is the moving receiver or rover . In order to achieve higher accuracy, a second receiver must be added - a base station. The base station must be set up over a known point and not move - it must be static. The base station receiver and the rover receiver both need to see at least the same four satellites at the same time. The higher number of common satellites, the better the accuracy and the faster the acquisition.

There is another component to make this all sing. At the same time both GNSS receivers are getting common satellite data, a correction must be broadcast from the base station to the rover (or more than one rover). This is typically accomplished with a radio signal.  Satellites, cellular connections and the internet can also be used.

Please see two of Joe Sass’s articles for more information:
“GNSS RTK Data Links”


“Why Standards? Interoperability through RTCM and NMEA”
As Joe points out in these articles, standards will produce the most interoperability. But in the interim, there are work-arounds as we will discuss later in the article.

Software, Software, Software

In addition to receivers seeing the same satellite constellations, delivering RTK corrections across a compatible radio method, there is software. Software plays a key role in a mixed GNSS receiver set up. One example (and there are many) is the software used to setup the base station, setup the rover, setup the radios and used to localize the site needs the ability to communicate to these multiple devices. This is accomplished through a device driver. If one software solution has multiple device drivers, these mixed tasks are easier due to a single software interface. For example, if a software can setup a Topcon base station along with the radios, localize the site, move the localization data to the rover system while also setting up that GNSS receiver and radio, the user/operator only has one user interface to learn.

Data file formats can be another challenge. Each GNSS receiver and software vendor may use different file formats to manage the system. It is paramount to understand the software’s compatibility with the different formats you may encounter when using multiple brands. File types may include localization files, surface files, line files, point files, road alignment files, etc.

Overview Contribution by MachineControlOnline Reader - Brad Hampton

In my article introduction, I wrote that Ive received several emails asking about mixing GNSS receiver brands. I had not taken the time to write until I received an email from MCO reader Brad Hampton, a senior surveyor at LNB Construction located in Merritt, British Columbia.  Brad offered information on how he has accomplished a compatible workflow using multiple brands of GNSS receivers and software.

Brads writes:


My name is Brad and I have been surveying for a construction company out of BC Canada called LNB Construction.

Something I have been able to accomplish in my 7 years is how to run Trimble-brand GPS machines off of a Topcon base.  I see many posts on the internet from surveyors and contractors wondering if this is possible... I thought maybe your website would be interested in contacting me so we could do an article on blending survey brands like this.

Brad Hampton < This email address is being protected from spambots. You need JavaScript enabled to view it. >

What a great opportunity to finally put this together with the help of an experienced professional. After several exchanges, Brad has offered the following overview of how he is using a Topcon base station with Trimble brand machine control systems. Brad has also been kind enough to allow me to post his name and email should anyone have any questions. A special thank you Brad for his contribution!


Setting up a Topcon GPS base to run Trimble Machine Control

- setup a Topcon GPS base running a low-split external PDL radio (none of this will work unless the radio is low-split)

- in the base setup, make sure the radio protocol is configured to 'TrimMark Base' and radio format is 'CMR+'

- you also need to find a common frequency between the PDL radio and the machine control radios - I found that 440.35 is in common between the

  systems that I use - note that 900mhz "SNR900" will not work with the following process - I use a Sitenet 450 and it functions fine

Perform a standard Topcon GPS localization of a site - make sure you name the points in a way that you can remember what order they were shot in.

    I use the control point name followed by a sequencial number (ie #20-1. #4801-2, #800-3, etc.)

Use 'Trimble Survey Controller' emulator for the next section:

    - create a new job using 'local site' and 'key in parameters'

        - projection is 'transverse mercator'

        - datum trans 'three parameter'

        - horizontal adjustment 'plane'

        - vertical adjustment 'inclined plane'

        - 'accept'

    - 'key in' and 'points' (after each point entry, make sure you click 'accept')

For the next 2 steps, enter the points in the order that you shot them, utilizing the system from above.

    - enter all northing, easting, and elevations (in 'grid' mode) of your control points from the Topcon control list

    - enter all lat, long, and heights (in 'WGS84' mode/use the same previous control point names but add "GPS" to the ends) using the localization data

      from your Topcon control list

    - 'esc' out

    - at main menu tap 'survey', 'RTK', then 'site calibration'

    - click 'add' and start pairing each grid co ordinate with it's WGS84 partner (make sure you match the same horizontal and vertical selections for each

      point as the Topcon Control file - the residuals usually aren't exactly the same but end up very close)

    - click 'apply' then 'esc'

    - at main menu click 'Files', 'Import/Export', then 'Export fixed file format'

    - select 'Trimble DC' as the export format and choose your file destination underneath that

Use Trimble Sitevision Office to export the site data for machine control and incorporate the DC that you just created.

Always confirm your machine control setup with a position check against the rover.  Remember to set the rover radio protocol to 'TrimMark Rover'

Again I would like to thank Brad for his contribution. If anyone has anything tips related to GNSS, machine control, etc., please email me at This email address is being protected from spambots. You need JavaScript enabled to view it. .



RTK GNSS systems as well as site solutions, are a symphony of hardware components, satellite constellations, communication protocols, antenna types, software user interfaces and device drivers. When it all comes together it is truly beautiful music. While an operator, mining engineer or contractor may not put it in these terms, they all agree 3D machine control technology takes their abilities and profits to new heights. The added flexibility of using multiple GNSS receivers empowers the user to create their desired solution and performance at a price point they choose. I am on my soapbox again.The more user driven solutions the manufacturers provide and the simpler processes that are made through cooperative standards, the faster the markets grow. That is good for all of us.


Randy Noland
Managing Editor/Cofounder
Machine Control Control Magazine
This email address is being protected from spambots. You need JavaScript enabled to view it.

References and Resources
How RTK GPS Works - Demonstration Video


Satellite Navigation


Real Time Kinematic (RTK)


NMEA 0183


Device Driver


Multi-Constellation GNSS/RNSS From the Perspective of High Accuracy Users in Australia


Commercial Viability of the GNSS-RTK Network Services


3D grade control systems explained


How does GPS positioning work?


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