Patent ID: 7165632

Claim:
In a system for tracking a boring tool which is moved in an underground region using a drill string having a length that extends to the boring tool and said boring tool having an overall orientation that is characterized by a pitch orientation, a yaw orientation and a roll orientation and which is steerable underground in the region using said roll orientation, said boring tool being configured for advancing in a straight ahead mode during a continuous roll and further being configured for advancing in a steering mode by moving the boring tool at a fixed roll orientation, a method comprising: establishing a maximum drill string curvature available in said steering mode within said region; advancing the boring tool over a path segment in said region using at least one of the straight ahead mode and the steering mode; establishing an averaged roll characteristic for movement of the boring tool along said path segment; determining a path segment pitch orientation based on at least one measured pitch orientation of said boring tool along said path segment; and using the maximum drill string curvature in combination with the averaged roll characteristic and the path segment pitch orientation, determining said yaw orientation of the boring tool.