What is GDOP and why is it important in navigation?

• A. Geometric Dilution of Precision; quantifies how satellite geometry affects position, velocity, and time accuracy; lower GDOP indicates better geometry.
• B. General Dilution of Pressure
• C. Global Distance of Optical Phases
• D. Graphical Data Optimization Parameter

Answer: (A)

Geometric Dilution of Precision describes how the arrangement of visible satellites affects how accurately a GNSS receiver can determine your position, velocity, and time. When satellites are well spread across the sky, the geometry is favorable, GDOP is low, and the solution is more precise. If satellites cluster together or are mostly near the horizon, the geometry is poor, GDOP rises, and the potential error in the PVT estimate increases. Because it combines the impact on all three components (and time) into a single number, GDOP is a handy measure of how reliable the navigation solution is and helps in decisions like selecting satellites or waiting for better geometry. The other terms listed don’t describe this concept and aren’t used to assess GNSS solution accuracy.