Move stamping closer to data reading. #104
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ValerioMagnago
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@ValerioMa thanks for the PR, makes sense. LGTM 👍 @ptruka FYI |
Before this commit the scan message was stamped just before publishing the data. In the LaserScan message of ros the timestamp in the header is the acquisition time of the first ray in the scan.
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behind #109 |
MichaelGrupp
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May 10, 2024
The previous timestamp patch in PR PepperlFuchs#104 subtracted the full scan time from the last point time of the _first_ packet to determine the scan timestamp. It has to be the time for a single packet instead. Otherwise, the timestamp is too far in the past. This is especially noticeable when the scan frequency is in a lower range like 10Hz, i.e. the scan timestamp would be 100ms off compared to other sensor modalities.
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At the moment the timestamp is added just before the data is published ( https://github.com/PepperlFuchs/pf_lidar_ros_driver/pull/104/files#diff-db3fd72df08186f3c4adfeb4c26aa1eb5526a4781c16d0603ff879d0fd2f2b86L81 ).
Synchronisation of the ROS system with the scanner, as requested in #23, is beyond the scope of this PR.
But the attempt here is to reduce the number of approximations by stamping the data when it is parsed. This time is closer to the ideal time at which the last scan point was sampled than the publication time. Also, since the stamp of the LaserScan message (http://docs.ros.org/en/api/sensor_msgs/html/msg/LaserScan.html) is the time of the first beam captured, it makes sense to remove the scan_time from the timestamp. If we do not do this, we will have more and more delays the longer the scan time is.