from typing import Union
from typing import Tuple


def ofname_tif(
    column: Union[str, Tuple[str, str]], size_x: int, size_y: int
) -> str:
    """
    Return a filename for an output GeoTIFF file.

    """
    if isinstance(column, tuple):
        output_name = '_'.join(column)
    else:
        output_name = column
    return f"insar_grid_{size_x}x{size_y}_{output_name}.tif"