What factors determine GNSS geometry quality?

• A. Satellite constellation geometry alone determines DOP.
• B. Elevation distribution only.
• C. Receiver position only.
• D. Satellite constellation geometry, elevation distribution, and receiver position.

Answer: (D)

GNSS geometry quality depends on how the satellites are spread around the receiver and how that geometry interacts with the receiver’s location. The distribution of satellites in the sky (constellation geometry) sets the baseline angles between lines of sight. If satellites cluster in one part of the sky or lie near the horizon, the geometry is poor and the geometry-related error amplification grows. Elevation distribution matters because high-elevation satellites provide better angular diversity and stronger, less obstructed signals, while many low-elevation satellites reduce the useful geometric separation. The receiver’s position also changes the angles to the same set of satellites; moving the receiver alters the geometry of the measurement equations and thus the potential error amplification. All three factors feed into the geometry matrix used in the position solution, which is quantified by DOP values. When satellites are well-distributed across the sky, including higher elevations, from a favorable receiver position, geometry quality is high (low DOP) and position accuracy improves; if any of these aspects are poor, geometry quality degrades (high DOP).