def METHOD_NAME(self):
    ny, nx, nz = np.array(self.resistivity.shape) + 1
    headerlines = [r'' + item + '\n' for item in ['GOCAD SGrid 1 ',
                                                  'HEADER {',
                                                  'name:{}'.format(
                                                      op.basename(self.fn)),
                                                  'ascii:on',
                                                  'double_precision_binary:off',
                                                  '}',
                                                  'GOCAD_ORIGINAL_COORDINATE_SYSTEM',
                                                  'NAME Default',
                                                  'AXIS_NAME "X" "Y" "Z"',
                                                  'AXIS_UNIT "m" "m" "m"',
                                                  'ZPOSITIVE Elevation',
                                                  'END_ORIGINAL_COORDINATE_SYSTEM',
                                                  'AXIS_N {} {} {} '.format(
                                                      ny, nx, nz),
                                                  'PROP_ALIGNMENT CELLS',
                                                  'ASCII_DATA_FILE {}'.format(
                                                      op.basename(self.ascii_data_file)),
                                                  '',
                                                  '',
                                                  'PROPERTY 1 "{}"'.format(
                                                      self.property_name),
                                                  'PROPERTY_CLASS 1 "{}"'.format(
                                                      self.property_name),
                                                  'PROPERTY_KIND 1 "Resistivity"',
                                                  'PROPERTY_CLASS_HEADER 1 "{}" '.format(
                                                      str.lower(self.property_name)) + '{',
                                                  'low_clip:1',
                                                  'high_clip:10000',
                                                  'pclip:99',
                                                  'colormap:flag',
                                                  'last_selected_folder:Property',
                                                  'scale_function:log10',
                                                  '*colormap*reverse:true',
                                                  '}',
                                                  'PROPERTY_SUBCLASS 1 QUANTITY Float',
                                                  'PROP_ORIGINAL_UNIT 1 ohm*m',
                                                  'PROP_UNIT 1 ohm*m',
                                                  'PROP_NO_DATA_VALUE 1 {}'.format(
                                                      self.no_data_value),
                                                  'PROP_ESIZE 1 4',
                                                  'END']]
    hdrfn = os.path.join(self.workdir,self.fn)
    if not hdrfn.endswith('.sg'):
        hdrfn += '.sg'
    print("saving sgrid to ",hdrfn)
    with open(hdrfn, 'w') as hdrfile:
        hdrfile.writelines(headerlines)