def tri_area(self, lons, lats):
        """
        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

        """
        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
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