def hgeo_to_hpot(h_geo, Re=6371000.0):
    """Calculates the geopotential altitude from the geometric altitude.
    
    Parameters
    ----------
    h_geo : float
        Geometric altitude.
    Re : float, optional
        Earth's radius (default is 6371000.0).
        
    Returns
    -------
    hpot : float
        Geopotential altitude.
    """
    
    return Re/(Re+h_geo)*h_geo