Chapter 5: Mobile Mapping Fundamentals

Nicolas MalloyAuthor: Nicolas R. Malloy


5.28 Geometric Dilution of Precision


The arrangement of satellites in the sky changes hour by hour. The specific positions of satellites overhead can cause a different type of error called geometric dilution of precision (GDOP). Satellites high in the sky and close together create larger areas of uncertainty.

The best arrangement to minimize GDOP is a satellite overhead with three other satellites evenly spaced and closer to the horizon. GDOP is expressed numerically as a multiplier of user equivalent range errors:

GDOP Description Application
1 Perfect, does not magnify UERE Military grade applications
2 -3 Excellent Civilian survey grade applications
4 – 6 Good Vehicle navigation, environmental resource management
7 + Poor Not recommended for positioning. Rough estimates only