图符提取是地形图自动输入的关键步骤，通过图符的提取可以得到地形图的许多重要信息。因此为实现地形图符的自动提取，提出了一种基于改进的形态学腐蚀运算的图符提取算法，该算法具有高识别率和较快的运行速度，并可克服线划图粘连引起的误识别。该算法适用于实际地形图自动输入系统，对于类似线划图图符提取的其它领域也有较好的应用前景。

Symbol separation is a key step of the automatic input of topographic map. A great deal of important information can be acquired through the pick up of symbols. Although there has been a lot of algorithms aiming at this question, they were all obsessed by the conglutination problem. In this paper we define a new kind of morphological erosion operation and propose a new symbol separation algorithm based on it. Experiment result shows that this algorithm provides high resolution and rapid speed, and it can get over the familiar conglutination problem between symbols and lines that is inextricable to the general symbol separation algorithms. Its performance has met the requisition of actual automatic input system of topographical map. Further more, with a few modifications of the program, it can be extended to the recognition of other analogous line drawing such as engineering blueprint. We could also combine it with traditional algorithms to achieve better proformance.