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The automatic recognition of trough lines is essential in automatic synoptic maps analysis, while trough line analysis mainly depends on manual analysis presently. In order to extract trough lines rapidly and accurately with isoline data, a trough point extraction method based on the DouglasPeucker algorithm is proposed. The algorithm extracts curve characteristic points as trough points through DouglasPeucker algorithm, which retains the characters and topology of isolines mostly, then connects trough points to construct candidate curves with the related principles according to isoline topological structure, finally, remove ridge lines in the candidate curves. The results show that this algorithm can realize the automatic recognition of trough lines.