Method for establishing the positions of a transmitter and detector in a region

In a system for tracking the position of a transmitter in the ground as the transmitter moves along an underground path which lies within a region, said transmitter being configured for transmitting an electromagnetic locating signal as a locating signal and said system including an above ground arrangement for receiving the electromagnetic locating signal for use in establishing the position of the transmitter, a method comprising:

• providing an above ground detector as part of said above ground arrangement which is configured for receiving said locating signal;
• locating the detector at an initial position in said region within a dipole range of said electromagnetic locating signal transmitted from the transmitter at a first, start position;
• receiving said electromagnetic locating signal using said detector with the transmitter at said start position to produce a first set of electromagnetic data;
• moving the transmitter to a second position;
• receiving said electromagnetic locating signal using said detector with said transmitter at said second position to produce a second set of electromagnetic data;
• and
• determining absolute positions of the detector and the transmitter within said region using certain information including said first and second sets of electromagnetic data.