new_contents: """
  Reduction to the pole
  ---------------------
  
  If the direction of magnetization is known, you can reduce a measured total
  field magnetic anomaly to the pole. Function
  :func:`fatiando.gravmag.transform.reduce_to_pole` implements the reduction
  using the FFT and allows using a magnetization direction that is different from
  the geomagnetic field direction. This example shows how to use it in this case.
  Use ``sinc=inc`` and ``sdec=dec`` if there is only induced magnetization.
  
  """
  from __future__ import division, print_function
  import matplotlib.pyplot as plt
  from fatiando.gravmag import prism, transform
  from fatiando.mesher import Prism
  from fatiando import gridder, utils
  
  # Create some synthetic magnetic data with a total magnetization that is
  # different from the geomagnetic field (so there is remanent magnetization or
  # some demagnetizing effect)
  inc, dec = -60, 23  # Geomagnetic field direction
  sinc, sdec = -30, -20  # Source magnetization direction
  mag = utils.ang2vec(1, sinc, sdec)
  model = [Prism(-1500, 1500, -500, 500, 0, 2000, {'magnetization': mag})]
  area = (-7e3, 7e3, -7e3, 7e3)
  shape = (100, 100)
  x, y, z = gridder.regular(area, shape, z=-300)
  data = prism.tf(x, y, z, model, inc, dec)
  
  # Reduce to the pole
  data_at_pole = transform.reduce_to_pole(x, y, data, shape, inc, dec, sinc,
                                          sdec)
  
  # Make some plots
  plt.figure(figsize=(8, 6))
  
  ax = plt.subplot(1, 2, 1)
  ax.set_title('Original data')
  ax.set_aspect('equal')
  tmp = ax.tricontourf(y/1000, x/1000, data, 30, cmap='RdBu_r')
  plt.colorbar(tmp, pad=0.1, aspect=30, orientation='horizontal').set_label('nT')
  ax.set_xlabel('y (km)')
  ax.set_ylabel('x (km)')
  ax.set_xlim(area[2]/1000, area[3]/1000)
  ax.set_ylim(area[0]/1000, area[1]/1000)
  
  ax = plt.subplot(1, 2, 2)
  ax.set_title('Reduced to the pole')
  ax.set_aspect('equal')
  tmp = ax.tricontourf(y/1000, x/1000, data_at_pole, 30, cmap='RdBu_r')
  plt.colorbar(tmp, pad=0.1, aspect=30, orientation='horizontal').set_label('nT')
  ax.set_xlabel('y (km)')
  ax.set_xlim(area[2]/1000, area[3]/1000)
  ax.set_ylim(area[0]/1000, area[1]/1000)
  
  plt.tight_layout()
  plt.show()
  
subject: Add a Gallery example of reduction to the pole (#390)