GNSS

GNSS (Global Navigation Satellite System) is a general term for satellite navigation systems that provide precise positioning anywhere on Earth. In surveying, GNSS has become one of the main measuring instruments.

Main GNSS systems:

• GPS (USA) - first and most widely used system
• GLONASS (Russia) - Russian satellite system
• Galileo (Europe) - European Union system
• BeiDou (China) - Chinese satellite system

GNSS in surveying:

Professional GNSS equipment provides:

• Centimeter precision - in RTK mode
• Millimeter precision - in static mode with post-processing
• Speed - point measurement in seconds
• Efficiency - no line of sight needed between points

GNSS measurement methods:

• RTK (Real Time Kinematic) - real-time measurements with base station
• Static measurement - prolonged observation for high-precision measurements
• Kinematic measurement - in motion with post-processing
• NRTK - network RTK using national base stations

LatPos system in Latvia:

Latvia operates LatPos - a permanent GNSS base station network that provides:

• Real-time corrections throughout Latvia
• Precision up to 1-2 cm horizontally and 2-3 cm vertically
• Data access via internet or GSM

GNSS limitations:

• Open sky visibility required
• Signal interference in forests and urban areas
• Lower precision in height determination
• Dependence on satellite geometry (GDOP)