GPS

GPS (Global Positioning System) is a satellite navigation system created by the US Department of Defense that provides precise location and time determination anywhere on Earth. Although GPS is just one of the GNSS systems, this name is often used as a synonym for all satellite navigation systems.

GPS system structure:

• Space segment - 24+ satellites in six orbits (approximately 20,200 km altitude)
• Control segment - ground stations monitoring and correcting the system
• User segment - GPS receivers (phones, measuring instruments, etc.)

GPS signals:

• L1 - civilian signals (1575.42 MHz)
• L2 - professional signals, improved precision
• L5 - newest signal for safety and precision

GPS precision:

• Standard GPS - 3-5 m (smartphones, navigators)
• DGPS - 0.5-1 m (with differential corrections)
• RTK GPS - 1-2 cm (professional surveying)
• Static GPS - millimeter precision (with post-processing)

GPS use in surveying:

• Land parcel surveying - boundary point coordinate determination
• Topography - detail surveying
• Construction stakeout - placing design in the field
• GIS data collection - object positioning
• Control measurements - verification of existing data

GPS limitations:

• Direct line of sight to satellites required
• Signal interference in forests, cities, tunnels
• Ionospheric and tropospheric effects on signal
• Multipath effect (signal reflection)

GPS vs GNSS:

Modern professional equipment uses multiple satellite systems simultaneously (GPS, GLONASS, Galileo, BeiDou), providing better availability and precision. This combined approach is called GNSS.