GNSS basics: how a position is calculated

Groundhawk knows its location by connecting to satellites. Satellites from several systems, including GPS, Galileo, GLONASS and BeiDou (together called GNSS), constantly send signals with their position and an exact time. The receiver measures how long each signal took to arrive and turns that into a distance to each satellite. With four or more satellites in view, it can calculate its position in 3D: east/west, north/south and height. On its own, this gives an accuracy of a few meters, because the signals are slowed and bent by the atmosphere and reflected by the surroundings. That is fine for car navigation, but not for documenting a cable in a trench.

RTK fix: from meters to centimeters

RTK (Real-Time Kinematic) positioning removes most of those errors. A reference station at a precisely known location sees the same satellites and the same errors, and sends corrections to the Groundhawk device over the mobile network, through a national or commercial correction service. When the device has enough good satellites and a steady correction stream, it reaches an RTK fix: a centimeter-level position, shown clearly in the app. If conditions are weaker, it drops to RTK float, with decimeter-level accuracy, and eventually to a standalone position.

For the customer, the fix is what makes the data trustworthy. Combined with Groundhawk's camera and sensor assistance, it lets the crew already on site document cable location and depth with about 10 cm accuracy in X, Y and Z, without a surveyor. The result is as-built data that meets operator and regulatory requirements, fewer disputes at handover, and cables that can be found reliably decades later.

Common GNSS and RTK issues on site

Most positioning problems come from a blocked sky view or a lost correction signal. Knowing them helps crews plan the scan and recognise when to wait for a fix. These issues affect all GNSS devices used to map, not just Groundhawk.

• Cities (urban canyons): tall buildings block satellites and reflect signals, which causes jumps or a slow fix.
• Forests and tree lines: dense, wet foliage weakens signals, so the fix can drop to float under heavy canopy.
• Bridges, tunnels and overhangs: the signal is lost completely and the fix must be regained afterwards.
• Deep or narrow trenches: trench walls and spoil heaps near the antenna cut off low satellites.
• Weak mobile coverage: RTK corrections arrive over the internet connection of a mobile network, so poor coverage in rural or remote areas means no fix.
• Distance from the reference station: accuracy degrades far from the nearest base station or outside the correction network's area. This does not have a major influence on Groundhawk unless used in very remote areas such as Lapland.
• Poor satellite geometry and space weather: few satellites spread across the sky, or strong ionospheric activity, reduce accuracy for periods of time. Groundhawk uses multiple satellites (GPS, Galileo, GLONASS and BeiDou) to tackle this and it rarely becomes an issue.
• Nearby interference: power lines, transformers and some radio equipment can disturb the signal.
• GNSS jamming: jamming interrupts the centimeter-level corrections required for RTK receivers, dropping the system from a fixed position to a float mode, or causing a total loss of position. Strength of the current jamming signals can be found ie. here: https://gpsjam.org/

Good practice: check for an RTK fix before scanning, keep the device's sky view as open as possible, and pause briefly after obstructions until the fix returns.