def compute_gcc(dataset):
    """Compute GCC vegetation index.

    Parameters
    ----------
    dataset : xarray dataset

    Returns
    -------
    xarray dataset
        Adds 'gcc' xr array to xr dataset.

    """
    b2 = dataset.band_data.sel(band="B2")
    b3 = dataset.band_data.sel(band="B3")
    b4 = dataset.band_data.sel(band="B4")
    gcc = b3 / (b2 + b3 + b4)
    return dataset.assign({"gcc": gcc})