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Velodyne does not appear to read hardware time stamp

asked 2015-01-12 19:14:21 -0600

brianthelion gravatar image

updated 2015-01-13 09:10:45 -0600

From the HDL-32E User's Manual & Programming Guide, pg 9:

Packet Format and Status Byte for GPS Time Stamping
The 6 extra bytes at the end of the HDL-32E data packet are used to report GPS timing. For every packet, the last 6 bytes are formatted as follows:
     4 bytes: 32 bit unsigned integer time stamp. This value represents microseconds from the top of the hour to the first laser firing in the packet.
     2 bytes: blank

Unless I am failing to follow the code, never touches the time stamp bytes in the data packet.

Question: Are we to assume that the time stamp reported by pcl_ros/bag_to_pcd is the time the UDP packet was received in software as opposed to the hardware-provided time stamp?

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answered 2015-01-12 20:34:53 -0600

Ryan gravatar image

I believe you are correct. The Velodyne driver was originally written for the -64 model which has a very similar protocol, but no GPS. I did the first validation of the -32 for Jack, because he only had a -64 on hand, and no changes were required to the base code. Since that wasn't really requested by anyone at the time (Clearpath being the only -32 user), the extra code to handle the GPS wasn't added.

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What's the best way to retrieve the hardware time stamp given that the driver isn't parsing it? Patch the driver? Something else?

brianthelion gravatar image brianthelion  ( 2015-01-13 17:03:13 -0600 )edit

Yes, I think you'd need to patch the driver. If you can make a patch that works with all the supported models, please submit a merge request so we can add it to the standard driver.

joq gravatar image joq  ( 2015-01-19 18:49:38 -0600 )edit

I was just wondering if this change been merged into the latest velodyne driver because the comments on file says HDL-64E? If it has been updated, does it work for the VLP16 as well?

i_robot_flight gravatar image i_robot_flight  ( 2017-10-20 09:23:28 -0600 )edit

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Asked: 2015-01-12 19:14:21 -0600

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Last updated: Jan 13 '15