Apparatus and methods for estimating an azimuth of at least part of a bottomhole assembly (BHA) in a borehole intersecting an earth formation, the BHA comprising magnetic material. Methods include conveying the BHA into the borehole; using a first sensor disposed on the BHA to produce a first measurement of a component of a magnetic field at a first borehole depth; estimating the axial component at the first borehole depth in dependence upon the first measurement; estimating an azimuth of at least a part of the BHA at the first borehole depth using the axial component; and controlling drilling operations with the BHA in dependence upon the azimuth. The magnetic field includes an axial component and a plurality of non-axial components unaligned with the axial component. The magnetic field is affected by the magnetic material and the first measurement is representative of at least one non-axial component of the plurality.