Patent ID: 8393414

Claim:
In a system for tracking the position of a sonde in the ground as the sonde moves along an underground path within a region, said sonde configured for transmitting an electromagnetic locating signal, a method comprising: locating at least two above ground detectors, each of which is configured for receiving said locating signal, at initial positions in the region within range of said electromagnetic locating signal transmitted from the sonde at an initial position of the sonde; measuring a tilt angle of each detector at each initial position; transmitting a relative locating signal from a first one of the detectors; receiving said relative locating signal using a second one of said detectors; determining the position of the second detector relative to the first detector based on the received relative locating signal; receiving said electromagnetic locating signal using said first and second detectors to produce electromagnetic data; and establishing initial coordinates of said detectors and said sonde within said region using certain information including the electromagnetic data and said tilt angles in conjunction with the relative position established between the detectors.