Azimuth determination while rotating

A system 100 for determining azimuth while drilling a wellbore comprising: a bottomhole assembly disposed in the wellbore comprising: a drill bit 112, a first magnetometer 118 for measuring magnetic toolface while drilling, a second magnetometer 124 for measuring cross-axial magnetic field, an accelerometer 120 for measuring acceleration to obtain gravity vectors; and an information handling system 130 operable to determine azimuth at a point in the wellbore using at least the magnetic toolface and the measurement of the cross- axial magnetic field. The information handing system may be operable to determine a calibrated cross-axial magnetic field measurement using the measurement of the cross-axial magnetic field from the second magnetometer and magnitude of x- and y- components of a magnetic field as measured by the first magnetometer and the second magnetometer while static.