Co-registration of fiducials for leadfields

[Will Findley]

As best I can tell, before calculating the leadfields for the forward model,
the sensor positions are adjusted by the center of the spherical head
approximation as such:

lines 201-205 in compute_leadfield.m

      if isfield(vol, 'o')
        % shift dipole and magnetometers to origin of sphere
        pos = pos - repmat(vol.o, Ndipoles, 1);
        pnt = pnt - repmat(vol.o, size(pnt,1), 1);
      end

However, I can't find where the modification occurs to vol.o (the sphere's
origin determined in read_ctf_hdm.m) to take into account aligning the
fiducials for the spherical head model to the head coil positions during the
scan.  Does anyone know where this calculation is performed?

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