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​What are the RTK Corrections?

​What are the RTK Corrections?

Posted by Dariusz Liszka on 8th Jun 2021

RTK Corrections are the ‘magic’ behind the high accuracy of surveying grade GNSS rovers. The corrections help to remove the errors caused by the (put the description from septentrio article here - evernote).

RTK Corrections can be produced by the single GNSS Base Station or by the sophisticated software, which calculates the corrections based on the readings of the network of the GNSS Reference Stations.

Calculating corrections

The technique of calculating the corrections involves the measurement of the satellite signal to remove the majority of GNSS type errors.

The calculation process consists of four phases: acquisition (Single or Autonomous), differential positioning (DGNSS), ambiguity ‘Float’ mode and ambiguity ‘Fixed’ mode

This alignment process goes through three phases: acquisition, ambiguity ‘Float’ mode and ambiguity ‘Fixed’ mode. Accuracy in Float mode is around 0.75-0.2 m and in Fixed mode it is 0.01-0.02 m. It is important to point out that accuracy is not the same as what you see in the standard deviation field in your software.

Zenith40 GNSS rover

Operators

There are four operators available on the Irish market. They use different infrastructure of the reference stations network around the country.

Hitechniques is a distributor of correction services from VRSNow Trimble. As the largest GNSS rovers hire operator in Ireland we’ve been able to find that VRSNow gives the most reliable corrections with the highest rate of availability. The coverage of the correction service is also the widest. Especially in the far west of the country where other networks fail VRSNow is still giving reliable corrections allowing the rover to reach fix position.

Why do you need the Internet to access RTK corrections?

The RTK corrections can be delivered to the rover in different ways. In very remote areas (no, I’m not talking about Donegal) of the globe professionals use UHF modems (radio transmission, like Walkie-Talkie) for this purpose. They need to set up the base station within the range of the radio connection. Costs of using this kind of set up are much higher than using the RTK corrections produced by the network of reference stations streamed through the Internet. The Network Rovers (the professional name of the rovers using the network RTK corrections from the internet) have different possibilities to get the corrections as well.

Rover receivers like Zenith35 Pro or Zenith40 can use internal cellular modems to connect to the internet and get the necessary data. In Zenith16 rover receiver, it is necessary to use the internet connection delivered by the logger. Some of the more exotic rovers use LoRa connection as well, but it is not widely used.

Zenith16 GPS receiver

How to connect your rover to the Internet?

There are so many different brands available on the market at this moment, that one could have a problem with choosing the right one. When it comes to the connectivity and the corrections there is important to have as many options as possible. This would give a piece of mind in a difficult Irish rural environment where the mobile reception is of poor quality.

The mobile internet can be delivered by:

  • Cellular modem inside the rover receiver (for example GeoMax Zenith35Pro, Zenith40)
  • Cellular modem in the tablet / data logger (Juniper Mesa3 Android, Samsung SM-T395 ActiveTab 2)
  • WiFi connection in the tablet / data logger (Juniper Mesa3 Android, Samsung SM-T395 ActiveTab 2)

The field software like Microsurvey FieldGenius and GeoMax X-PAD, both allow the use of the internet connection from the tablet / data logger or from the rover. This allows to further reduce costs of the equipment by choosing, for example Zenith16 which doesn’t have cellular modem but can easily download the corrections through WiFi or internal tablet mobile internet connection.

Choosing the right mobile internet provider is also important. Hitechniques offers MOS2 SIM Cards (Multi-operator mobile internet provider) which can connect with every available network infrastructure in Ireland. The MOS2 service is fully supported by Hitechniques. Any other provider SIM Card can be used as well. Important details which have to be obtained from the provider are: APN server name, APN username and password.

In the next article we will discuss some of the important features in data loggers and what’s hot at the moment.

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Have any questions? Email us at info@hitechniques.ie