In order for the robot to paint accurately, it is necessary for it to know its exact position at all times. The robot does this by utilizing a number of interconnected technologies in the field of geopositioning.
In short, the accuracy with which the GNSS receiver can determine its position depends on the number of satellites it can receive signals from - the more the better. Using the signals from multiple satellites, the receiver performs a process called triangulation. It calculates the distance to each satellite based on how long it took for the signals to arrive, and then combines the distance information from all the satellites to calculate its exact position in three-dimensional space (latitude, longitude, and altitude).
However, disturbances in the atmosphere makes the GNSS signal less precise. This is mitigated by continuously comparing the received signals with correction data received over the internet from so called NTRIP casters.
For a basic introduction to the central technologies, see below.
Image: RTK is a specific form of real-time differential GNSS that provides very high levels of accuracy. NTRIP is a protocol used to transmit correction data, and it can be used in conjunction with RTK to facilitate wide-area coverage and real-time correction delivery over the internet.
What is GNSS?
Satellite navigation, or Satnav, is a system that uses satellites to provide autonomous geopositioning. A satellite navigation system with global coverage is termed a Global Navigation Satellite System (GNSS).
GNSS refers to a constellation of satellites providing signals from space that transmit positioning and timing data to GNSS receivers. The receivers then use this data to determine their location.
As of 2023, four global systems are operational:
- The US Global Positioning System (GPS)
- Russia's Global Navigation Satellite System (GLONASS)
- China's BeiDou Navigation Satellite System (BeiDou is Chinese for the constellation Ursa Major)
- The European Union's Galileo (named after Galileo Galilei)
In everyday language, the acronym GPS is often used when talking about satellite navigation, as GPS is the oldest and most well-known of the four GNSS systems. However, almost all modern GNSS receivers uses all four GNSS systems.
What is DGPS?
Differential Global Positioning System (DGPS) is a technique used to improve the accuracy of GNSS (Global Navigation Satellite System) measurements. It's especially important in applications where very high levels of accuracy are required, such as painting your sports fields.
DGPS involves setting up a reference station with a known, precisely surveyed location. This station calculates the errors in GNSS signals and generates correction data. This data is then broadcast to nearby mobile GNSS receivers, which then apply the corrections to their own measurements.
Correction data in DGPS is typically broadcast over radio signals directly from the reference station to the mobile receivers.
What is RTK (Real-Time Kinematic)?
RTK is a more advanced form of DGPS that provides even higher levels of accuracy in real-time. RTK also uses a reference station, but it continuously compares its own position with the known position. It calculates correction data in real-time and sends it to the mobile receiver, allowing for centimeter-level accuracy.
RTK networks of fixed reference stations extend the use of RTK to a larger area containing a network of reference stations. Operational reliability and accuracy depend on the density and capabilities of the reference-station network.
RTK can achieve centimeter-level accuracy, making it suitable for very precise applications such as painting sports fields. RTK correction data is typically transmitted using Ntrip.
What is NTRIP?
Ntrip (Networked Transport of RTCM via Internet Protocol) is a protocol used to transmit correction data, used in conjunction with both DGPS and RTK to facilitate wide-area coverage and real-time correction delivery over the internet. NTRIP can support various levels of accuracy, depending on the specific implementation, but it is capable of providing centimeter-level accuracy when used in conjunction with RTK.
NTRIP relies on a network of reference stations and a centralized server (NTRIP Caster). The reference stations send correction data to the caster, which then distributes it to mobile GNSS receivers via the internet.