利用多级汇水盆地在频率域(或波数域)中的频率差异，通过滤波方法逐级分离，并提取它们。

In this paper, multilevel water gathering basins are separated and extracted automatically with filtering from geographic map based upon their differences in frequency domain.

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因此，作者将二维扇形滤波方法做了近一步的改善，引入了频率—波数域内带通切饼式滤波方法。

So the author improves the 2-d sector filtering method, introduces the bang-transit and cake-cut filtering method in frequency - wave count area.

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