code: def tri_area(self, lons, lats):
          
          lons, lats = self._check_integrity(lons, lats)
  
          # translate to unit sphere
          x, y, z = _stripack.trans(lats, lons)
  
          # compute area
          area = _stripack.areas(x, y, z)
  
          return area
docs: Calculate the area enclosed by 3 points on the unit sphere.
  
          Parameters
          ----------
           lons : array of floats, shape (3)
              longitudinal coordinates in radians
           lats : array of floats, shape (3)
              latitudinal coordinates in radians
  
          Returns
          -------
           area : float
              area of triangle on the unit sphere