What does DOP stand for in GPS and what does it measure?

• A. Degree Of Position; a measure of the geometric strength of the satellite configuration.
• B. Data Offset Parameter; a measure of timing stability.
• C. Dilation Of Precision; a measure of the geometric strength of the satellite configuration.
• D. Dilution Of Precision; a measure of the geometric strength of the satellite configuration.

Answer: (D)

DOP stands for Dilution Of Precision, and it measures how the geometry of the visible satellites affects the potential accuracy of your GPS solution. When satellites are well spread across the sky, the geometry is strong, so measurement errors have less impact and the position (and time) estimates are more precise, giving a lower DOP. When satellites are clustered or near the horizon, the geometry is weak, errors get amplified, and the DOP is higher, indicating less reliable results. Different forms exist (PDOP for position, HDOP horizontal, VDOP vertical, TDOP time) but they all reflect how satellite geometry dilutes precision.