docs: def _flds_shape(fieldname, header):
      """Compute shape of flds variable."""
      shp = list(header['nts'])
      shp.append(header['ntb'])
      # probably a better way to handle this
      if fieldname == 'Velocity':
          shp.insert(0, 3)
          # extra points
          header['xp'] = int(header['nts'][0] != 1)
          shp[1] += header['xp']
          header['yp'] = int(header['nts'][1] != 1)
          shp[2] += header['yp']
          header['zp'] = 1
          header['xyp'] = 1
      else:
          shp.insert(0, 1)
          header['xp'] = 0
          header['yp'] = 0
          header['zp'] = 0
          header['xyp'] = 0
      return shp