Correction messages from a network of permanent base stations (RTK network) are received using the internet, either Wi-Fi or a 4G cellular connection. RTK network solutions (paid or free) are particularly successful in regions with dense deployment of permanent base receivers, such as Europe.
Depending on the range to the nearest reference station (< 40 km), position accuracies of within a centimeter can be achieved using Network RTK.
Correction message calculation used by Network RTK overcome the range limitation of a single base station. This is an advantage if testing is conducted tens of kilometres away from the base station, over large changes in elevation or where topographical obstacles could get in the way.
The VBOX NTRIP Modem enables the roving VBOX unit, or any other RTK-enabled device, to send its position to the stations within the network – just as it would to a single VBOX Base Station. The NTRIP service provider will then calculate the appropriate corrections for the VBOX’s location based on the data from nearby reference stations. This correction information is then returned to the VBOX in the same RTCM format as is used for a single fixed base station.
In order to access NTRIP correction services, you have to register and subscribe to a cellular data plan with your local NTRIP provider, such as Topnet in the UK and Germany, Swepos in Sweden or Unavco in the USA.
NTRIP networks are growing in size and capability. Some networks are operated by the state, free of charge, while others are privately operated and can require a subscription fee.
Network RTK utilises one or more Continuous Operating Reference Stations (CORS) to provide RTK data to a GNSS rover, usually via mobile internet. The most common method of Network RTK involves a two-way communication link which allows the roving vehicle to send its position to a service provider that is monitoring satellite observations from several reference stations around a country.