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What does "timestamp" of "header" in hokuyo's scan data?

asked 2016-01-12 04:53:03 -0500

I'm wondering what timestamp in hokuyo's sensor_msgs::LaserScan does mean. Is the time at first scan ray is measured? Or is the time at last scan ray is measured?

I know there is calibration function of latency between hokuyo and host PC in hokuyo node. But I cannot understand how the function works. Could you explain to me? Thanks in advance.

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answered 2016-01-12 06:58:10 -0500

updated 2016-01-12 06:58:27 -0500

The timestamp is the the time of the first ray/distance measurement in a scan. Note this is also stated in the comments of the sensors_msgs/LaserScan message definition.

The time calibration performs some sending of messages back and forth between scanner and host similar to NTP time synchronization. There is some more info here on page 27 of the UTM-30LX-EW protocol documentation.

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Thank you ~~ May I ask one more? As far, the timestamp is the first ray measurement in a scan. Is the timestamp based on host PC timer by time calibration? There are two timer, in hokuyo and in host PC.

claid00 gravatar image claid00  ( 2016-01-12 07:55:35 -0500 )edit

Yes, the driver node should take care of publishing the proper ROS timestamp for the message, based on the preceding time calibration. For details you have to look at the code.

Stefan Kohlbrecher gravatar image Stefan Kohlbrecher  ( 2016-01-12 07:59:06 -0500 )edit

Thank you~ The timestamp of encoder data from rosaria is also based on host PC. In rosaria code, the timestamp of encoder is updated by ros::Time.now () just before publishing. Am I right?

claid00 gravatar image claid00  ( 2016-01-12 08:21:11 -0500 )edit

Don't know, you'll have to look at the code. But just taking ros::Time::now() is an approach that's commonly taken if no complicated sync as with the hokuyo is done.

Stefan Kohlbrecher gravatar image Stefan Kohlbrecher  ( 2016-01-12 09:31:49 -0500 )edit

Thank you~ I'll have to look at the code. Thanks~

claid00 gravatar image claid00  ( 2016-01-12 20:08:55 -0500 )edit

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Asked: 2016-01-12 04:53:03 -0500

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Last updated: Jan 12 '16