In GNSS geometry, what does PDOP quantify?

• A. TDOP quantifies time accuracy.
• B. PDOP quantifies the effect of satellite geometry on 3D position accuracy.
• C. HDOP quantifies horizontal accuracy only.
• D. VDOP has no physical meaning.

Answer: (B)

PDOP captures how satellite geometry influences the accuracy of the 3D position solution in GNSS. When you solve for x, y, z plus the receiver clock bias using pseudorange measurements from multiple satellites, the way those satellites are spread across the sky affects how measurement errors propagate into the estimated position. Broad, well-distributed geometry yields a smaller, more favorable PDOP, meaning tighter 3D position uncertainties. If the satellites are clustered or low on the horizon, the geometry degrades, PDOP rises, and the potential 3D accuracy worsens. PDOP thus provides a single number that summarizes the combined effect of geometry on the 3D position, while other DOPs (HDOP, VDOP, TDOP) describe the separate contributions to horizontal, vertical, and time accuracy.