what the scale of time stamp in LaserScan topic??

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hi, i'm making some codes wrt human leg tracker with python and turtlebot2 using kinect2_sensor. (using ROS kinetic in Ububtu 16.04)

To predict human's state correctly, I have to know a time interval between previous and next position.

And I'm going to use [time stamp] variables of LaserScan topic.

But I don't know how big the scale of it is. I mean, I tried to get LaserScan topic and save it as csv file, but the values of [time stamp] was too high to accept. (ex. 1.56704904268227E+018 )

I also calculated time intervals between each other, and still unacceptable was the values of them.

Meanwhile, I have read at ROS wiki that the scale of time stamps would be [seconds] or [nano_seconds]. Could it's scale be nano seconds? If so, the time intervals would be acceptable.

[smple]

field.header.stamp              (time interval) [ns] --->[s]   (maybe???)

1.56704904268227E+018 -

1.56704904294911E+018 ,0.266849792

1.56704904325004E+018 ,0.300928

have a nice day~ :)