spd描述子，ACO算法匹配，文件中包含其他的描述子（形状上下文。。。），同时距离函数包括欧式距离和卡方距离(The SPD descr iptor matches the ACO algorithm, and the file contains other descr iptors (shape context) At the same time, the distance function includes Euclidean distance and chi square distance