message_filter

# wiki
http://wiki.ros.org/message_filters
# blog
https://blog.csdn.net/start_from_scratch/article/details/52337689

A set of message filters which take in messages and may output those messages at a later time, based on the conditions that filter needs met.

相当于修改订阅话题的时间戳，在之后一同发布，软消息同步。