Short answer
A geometric quality metric expressing how the spatial distribution of visible satellites amplifies ranging errors into position errors. Lower is better: PDOP < 4 is good, < 2 is excellent. PDOP depends only on satellite geometry, not signal quality.
Detailed explanation
DOP factors quantify the geometric quality of the visible satellite distribution. The principle: a position fix triangulates from N ≥ 4 range measurements; if the satellites are clustered together in the sky, small range errors produce large position errors (high DOP); if they're spread across the upper hemisphere, the same range errors produce small position errors (low DOP).
Standard DOP variants: GDOP (geometric, including time), PDOP (position 3D), HDOP (horizontal), VDOP (vertical), TDOP (time). PDOP < 4 is generally regarded as good for surveying; < 2 is excellent and rare. Above 6 the geometry is poor and you should wait for better — or accept degraded precision.
Tracking more constellations directly reduces DOP. A receiver tracking GPS only sees maybe 7–9 satellites at a clean rooftop site; adding GLONASS, Galileo, and BeiDou pushes that into 20–35 satellites simultaneously, dropping PDOP from 2–4 to 1–1.5 routinely. This is the geometric argument for multi-constellation tracking — independent of any signal-quality improvement.
DOP is independent of signal quality (C/N₀, multipath, ionosphere). A pristine sky with poor satellite geometry produces a high-DOP fix; a noisy environment with great geometry produces a low-DOP fix. The total expected position error is roughly: UERE × DOP, where UERE is the user equivalent range error (typically 1–5 m).
Where you'll see this
High-Precision GNSS Measurement
Browse product lineRelated terms
TTFF
The elapsed time from receiver power-on (or warm/cold start) to the first valid position fix. Cold start (no almanac, no recent position, no time) is typically 30–60 seconds; warm start (with valid almanac and approximate position) is 5–15 seconds; hot start (with current ephemeris) is <1 second.
GNSS
Umbrella term for any constellation of satellites providing global positioning, navigation, and timing. The four global GNSS systems are GPS (US), GLONASS (Russia), Galileo (EU), and BeiDou (China); QZSS (Japan) and NavIC (India) are regional.
C/N₀
The ratio of received signal power to noise power spectral density at the receiver. Expressed in dB-Hz (because the ratio has units of Hz). A clean rooftop GPS L1 receiver should see 45–50 dB-Hz on strong satellites; below 25 dB-Hz the receiver loses track.