Helmet metal mass compensation for helmet-mounted sighting system

An electromagnetic system for utilizing electromagnetic field vectors in determining the orientation of a helmet worn by the pilot of a vehicle, and for compensating for distortions of said electromagnetic field vectors caused by the metal mass of the helmet, the system comprising:

• transmitting means for transmitting said electromagnetic field vectors, said transmitting means including a transmitting antenna having at least two transmitting coils;
• a receiving antenna having three non-coplanar receiving coils fixed to said helmet for sensing said electromagnetic field vectors transmitted by said transmitting antenna;
• orientation determining means connected to said receiving antenna and to said transmitting means for iteratively determining a compensated orientation matrix for the receiving antenna by relying upon the rotation matrix for the rotation of the receiving antenna from the transmitting antenna of a previous iteration, said compensated orientation matrix being comprised of an orientation matrix which is compensated for distortions of said electromagnetic field vectors caused by helmet metal mass, said orientation matrix and said rotation matrix being based upon both the transmitted electromagnetic field vectors and the sensed electromagnetic field vectors;
• and,
• output means connected to said orientation determining means for providing an output signal for the control of a vehicle apparatus.