def grid_model_params_ria(lvgd):
    """Determine grid model parameters for LV grids of sectors
    retail/industrial and agricultural
    
    Parameters
    ----------
    lvgd : LVGridDistrictDing0
        Low-voltage grid district object

    Returns
    -------
    :obj:`dict`
        Structural description of (parts of) LV grid topology
    """

    # Choose retail/industrial and agricultural grid model
    model_params_ria = {}
    if ((lvgd.sector_count_retail +
             lvgd.sector_count_industrial > 0) or
            (lvgd.peak_load_retail +
                 lvgd.peak_load_industrial > 0)):
        model_params_ria['retail/industrial'] = select_grid_model_ria(
            lvgd, 'retail/industrial')
    else:
        model_params_ria['retail/industrial'] = None

    if ((lvgd.sector_count_agricultural > 0) or
            (lvgd.peak_load_agricultural > 0)):
        model_params_ria['agricultural'] = select_grid_model_ria(lvgd,
                                                                 'agricultural')
    else:
        model_params_ria['agricultural'] = None

    return model_params_ria