5.3 - GPS ERRORS

Basic geometry itself can magnify these other errors with a principle called Geometric Dilution of Precision or GDOP. It sounds complicated but the principle is quite simple: there are usually more satellites available than a receiver needs to fix a position, so the receiver picks a few and ignores the rest. If it picks satellites that are close together in the sky the intersecting circles that define a position will cross at very shallow angles. That increases the gray area or error margin around a position. If it picks satellites that are widely separated the circles intersect at almost right angles and that minimizes the error region. Good receivers determine which satellites will give the lowest GDOP.