A system for mapping a magnetic field in a volume of interest, the system includes a magnetic field transmitter, generating a magnetic field in the volume of interest, at least one freestanding magnetic field detector, operative to freely move within the volume of interest, the at least one freestanding magnetic field detector acquiring measurements of the flux of the magnetic field at a plurality of poses, and a processor, coupled with the magnetic field detector, the processor re estimating parameters characterizing the magnetic field model according to deviations between the measurements of the flux of the magnetic field and according to predictions of the flux, the predictions being determined according to a stored magnetic field model, thereby, the processor estimating a new magnetic field model.