def visibilities(self):
        """
        Return the array of visibilities, where each item is a scalar/float
        between 0 (completely hidden/invisible) and 1 (completely visible).

        (Nx1)
        """
        if self._visibilities is not None:
            return self._visibilities
        else:
            return np.ones(self.Ntriangles)
Return the array of visibilities, where each item is a scalar/float
        between 0 (completely hidden/invisible) and 1 (completely visible).

        (Nx1)