def coords_patch(mask, idens=6,
                 west=0, east=360, south=-90, north=90):
    import numpy as np

    idens = int(idens)

    ny, nx = mask.shape

    wlon = float(east - west) / nx
    wlat = float(north - south) / ny

    lats_all = south + wlat*(np.arange(ny)+0.5)
    lons_all = west + wlon*(np.arange(nx)+0.5)
    lons_all, lats_all = np.meshgrid(lons_all, lats_all)

    mask_shade = np.zeros((ny, nx), dtype='int32')
    mask_shade[::int(idens*2), ::int(idens*2)] = 1
    mask_shade[idens::int(idens*2), idens::int(idens*2)] = 1
    mask_shade[~mask] = 0
    lons = lons_all[mask_shade == 1]
    lats = lats_all[mask_shade == 1]

    return (lons, lats)