Tracking positions of personnel, vehicles, and inanimate objects
A device rotates at least one static magnetic field about an axis, producing a rotating magnetic dipole field, and is movable in relation to the surface of the ground. The field is periodically sensed using a receiver to produce a receiver output responsive to the field. A positional relationship between the receiver and the device is monitored using the output. In one aspect, changing the positional relationship, by moving the device nearer to a boring tool which supports the receiver, causes an increase in accuracy of depth determination. In another aspect, determination of an actual overhead position of the boring tool, and its application, are described. Use of a plurality of measurements over at least one-half revolution of each magnet is disclosed. Establishing a surface radial direction toward a boring tool and resolution of multi-valued parameters is described. Calibration techniques, as well as a three transmitter configuration are also described.
1. A calibration procedure, comprising:
positioning a transmitter, which is configured for rotating a magnet about an axis in a way which produces a rotating magnetic dipole field, in an at least temporarily fixed position and orientation;
arranging a receiver at a distance D from the transmitter at least approximately in a predetermined positional relationship with the transmitter;
using said receiver to periodically sense a set of total flux intensities in three dimensions, of said rotating magnetic dipole field, successively through a plurality of angularly distributed rotation angles of said magnet sufficient to characterize the total flux intensity with rotation of the rotating magnetic dipole field; and
using the set of total flux intensities in conjunction with distance D to determine a dipole strength m of the rotating magnetic dipole field.
2. The method of claim 1 wherein said receiver is arranged at distance D from the transmitter at least approximately on said axis and said set of total flux intensities is used to determine an average flux intensity for use with distance D to determine the dipole strength m of the rotating magnetic dipole field.
3. The method of claim 2 including using
m=D 3 B av
where B av is the average flux intensity based on said plurality of total flux intensities.
4. The method of claim 1 wherein said receiver is arranged at distance D from the transmitter at least approximately in a location through which said dipole axis passes during rotation and said set of total flux intensities is used to determine at least one of a minimum flux intensity and a maximum flux intensity for use with D to establish the dipole strength m of the rotating magnetic dipole field.
5. The method of claim 4 including using at least one of the expressions
m=D 3 B min , and
m=0.5D 3 B max
to determine the dipole field strength where B min and B max are the minimum and maximum flux intensities, respectively.