GNSS positioning techniques are the methods used to determine a user's three-dimensional (3D) position, velocity, and time by processing signals transmitted by orbiting satellites. The fundamental principle involves measuring the apparent distance (pseudorange) to at least four satellites to solve for the three receiver coordinates and the receiver clock offset. Positioning methods are generally categorized based on the measurements they use and their resulting accuracy: 1. Standard Point Positioning (SPP) SPP is a code-based positioning technique that uses pseudorange measurements (R). • Accuracy and Modeling: SPP typically achieves coordinate accuracy of several metres. To achieve this, errors such as satellite clock offsets, atmospheric delays (tropospheric and ionospheric), and instrumental delays are modeled. For single-frequency users, the broadcast Klobuchar ionospheric model is often used. • Process: The technique solves a nonlinear system by iteratively linearizing the geometric range around an approximate position and solving the resulting navigation equations (linear system y=Gx) using parameter estimation techniques such as least squares or Kalman filtering. 2. Precise Point Positioning (PPP) PPP is an advanced technique that utilizes both code and carrier phase measurements (R and Φ) to target high-accuracy positioning. • Accuracy and Modeling: PPP aims for centimetre-level accuracy in static positioning or decimetre-level (or better) in kinematic positioning. This requires accurate measurement modelling of all delay terms (including Earth deformation and antenna biases). • Key Requirements: PPP typically uses the ionosphere-free combination of dual-frequency signals to eliminate most ionospheric refraction. It relies on precise satellite orbits and clocks (such as those from IGS) rather than broadcast ephemerides. The receiver estimates the carrier phase ambiguities as real numbers (floating ambiguities). 3. Advanced Techniques (Differential and Fast PPP) Other techniques build upon PPP principles to improve speed and accuracy: • Differential Positioning (RTK/WARTK): These methods, such as Real-Time Kinematics (RTK) and Wide-Area Real-Time Kinematics (WARTK), rely on fixing the carrier phase ambiguities to their integer values. They often use double-differenced measurements between pairs of satellites and receivers to cancel out common errors, enabling centimetre-level positioning. • Fast Precise Point Positioning (F-PPP): This approach uses accurate external products, such as precise ionospheric corrections computed from a wide-area network, to accelerate the filter convergence time from approximately one hour to a few minutes, achieving better than 10 cm accuracy quickly. In essence, positioning techniques range from simple, real-time code solutions (SPP) suitable for standard navigation, to complex carrier-based solutions (PPP) using precise external products for geodetic accuracy.