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我正在尝试获取特定 ROS 消息的时间戳，将其记录在文件中，读取文件并恢复原始时间戳。至今未果。

这是我的代码

import os
import os.path
import rosbag
from sensor_msgs.msg import Image

import rospy

IMG_DIRNAME = '/the/root/to/bags/'

#we get only one published topic time and quit
def main():
    rosbag_file = 'thebag.bag'
    rosbag_file= os.path.join(IMG_DIRNAME,rosbag_file)
    for topic, msg, t in  rosbag.Bag(rosbag_file).read_messages():
        if topic == '/the/topic/image':
            print(".")
            return t


if __name__ == '__main__':
    try:
        time_stamp= main()    #I got the time stamp
        print("original ",time_stamp)
        print(time_stamp)
        print(time_stamp.secs)
        print(time_stamp.nsecs)
        print("recorded ",time_stamp.to_sec())
        print(time_stamp.to_sec())
        print("just to show ",time_stamp.to_nsec())

        ts=time_stamp.to_sec()

        #Here we record it in a file
        with open("afile.txt",'w') as f:
            f.write('{0}\n'.format(ts))
        
        with open("afile.txt",'r') as f:
            new_ts=float(f.read())
        

        time_new= rospy.Time.from_sec(new_ts)
        print("recovered ", time_new)
        print(time_new)
        print(time_new.secs)
        print(time_new.nsecs)

        print("==================================")
        print("other record",time_stamp.to_nsec())
        print(time_stamp.to_nsec())
        tns=time_stamp.to_nsec()
        #Here we record it in a file
        with open("afile2.txt",'w') as f:
            f.write('{0}\n'.format(tns))
        
        with open("afile2.txt",'r') as f:
            ff=f.read().strip("\n")
            print("read as")
            print(ff)
            new_tns=float(ff)

        print(new_tns)
        time_new_ns= rospy.Time(new_tns)
        print("recovered",time_new_ns)
        print(time_new_ns)
        print(time_new_ns.secs)  
        print(time_new_ns.nsecs)

结果我得到了

.
('original ', rospy.Time[1625151029987577614])
1625151029987577614
1625151029
987577614
('recorded ', 1625151029.9875777)
1625151029.99
('just to show ', 1625151029987577614)
('recovered ', rospy.Time[1625151029990000009])
1625151029990000009
1625151029
990000009
==================================
('other record', 1625151029987577614)
1625151029987577614
read as
1625151029987577614
1.62515102999e+18
('recovered', rospy.Time[1625151029987577600000000000])
1625151029987577600000000000
1625151029987577600
0

所以你可以看到，首先我得到了时间戳（原始）并记录了转换为秒（1625151029.99）。我将它记录到一个文件中（其中记录了该数字），恢复的时间戳与原始时间戳不同（ns 部分从 987577614 变为 990000009）。我想这是由于进行了to_sec转换

为了纠正这一点，我做了第二部分（在===之后）。我记录了我读取的 nsecs 数（1625151029987577614），首先正确地作为一个字符串，然后作为一个浮点数（以科学计数法显示）但在最后一部分（“恢复”）我不知道如何正确转换这个数字到 ROS 时间。我得到的价值是完全错误的

如何在此处获取原始时间戳？

编辑：我试过

print("recalculated")
tt=rospy.Time( int(new_tns //1000000000), int(new_tns%1000000000))
print("recovered",tt)
print(tt)
print(tt.secs)  
print(tt.nsecs)

但是虽然更接近原作了，但还是不明白

recalculated
('recovered', rospy.Time[1625151029987577600])
1625151029987577600
1625151029
987577600

另外，不能是一个更简单和正确的方法吗？

4

1 回答 1

0

您遇到的问题实际上来自使用time_new.nsecs不正确。您的期望是nsecs显示自纪元以来的总时间（以纳秒为单位）。然而，这个字段实际上显示了nano seconds since seconds (since epoch)。因此，您只是在time_new.secs. 如果您想进行完整的对话，请始终使用to_secs()and to_nsecs()。

于 2021-08-18T13:03:25.600 回答