该代码将xml文件中的图片尺寸信息和物体位置信息统一进行处理，物体位置会转换成0～1之间的比例，物体名字会根据label_map转换成一个数字列表，结果会存入tfrecord中。(The code will process the image size information and object location information in the XML file uniformly, and the position of the object will be converted to the ratio of 0~1. The name of the object will be converted to a digital list based on label_map, and the result will be stored in tfrecord.)