def calc_res(raster):
    """Calculate the resolution of xarray.DataArray raster and return it as the
    two-tuple (xres, yres).
    """
    h, w = raster.shape[-2:]
    ydim, xdim = raster.dims[-2:]
    xcoords = raster[xdim].values
    ycoords = raster[ydim].values
    xres = (xcoords[-1] - xcoords[0]) / (w - 1)
    yres = (ycoords[0] - ycoords[-1]) / (h - 1)
    return xres, yres
