  Current knowledge about stellar magnetic fields relies almost entirely on
circular polarization observations. Few objects have been observed in all four
Stokes parameters. The magnetic Ap star HD 24712 (DO Eri, HR 1217) was recently
observed in the Stokes IQUV parameters with the HARPSpol instrument at the
3.6-m ESO telescope as part of our project at investigating Ap stars in all
four Stokes parameters. The resulting spectra have dense phase coverage,
resolving power > 10^5, and S/N ratio of 300-600. These are the highest quality
full Stokes observations obtained for any star other than the Sun.
  We present preliminary results from magnetic Doppler imaging of HD 24712.
This analysis is the first step towards obtaining detailed 3-D maps of magnetic
fields and abundance structures for HD 24712 and other Ap stars that we
currently observe with HARPSpol.
