道格拉斯数据压缩算法。 算法特征：1.在不扰乱拓扑关系的前提下，对采样点数据进行合理的抽稀 2.对矢量坐标数据进行重新进行编码，以减少所需要的存储空间 3.矢量数据的压缩往往是不可逆的，数据压缩后，数据量变小了，数据的精度降低了-Douglas data compression algorithm. Algorithm characteristics: 1. In the relationship does not disturb the topology under the premise of sampling point data of a reasonable pumping dilute 2. Of vector coordinates of the data re-encoding, in order to reduce the required storage space 3. Vector data compression is often irreversible and data compression, the smaller quantity of data, data accuracy reduces