VLP-16 scan registration using IMU/GPS

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Hello,

I am trying to register scans from VLP-16 using pose data from INS.

In my setup I have a VLP-16 and a GPS aided INS (IMU+GPS). Their clocks are synchronized by providing INS's GPRMC and 1PPS signals to VLP-16. Both VLP-16 and INS raw data packets have the timestamp. The INS outputs at 200Hz but unfortunately at this time to get RTK level precision I need to post process the data several hours after the scan is completed. This means that I also need to record VLP-16's scans to .pcap files to process at the time when INS data becomes available.

I wrote a ROS node that parses post processed pose solutions and publishes messages that contain the pose to be used for computing tf transforms. If I understand this correctly, transforms' timestamps are used to match against data (and in my case the data is VLP-16's pointcloud2 messages). I assume that both transform messages and pointcloud2 messages need to have timestamps that come from sensors' clocks (that are synchronized as described above). My first question is whether this is correct :). If so, then can Velodyne driver use the sensor's timestamps (not ROS clock) when it populates the stamp in pointcloud2's header?

I read several discussions (issue 15, issue 57) that seemed to be related to my question but am not sure if it covers my use case.

Thank you.